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									Chapter 2

THE CHEMICAL LEVEL OF ORGANIZATION

Chapter Synopsis

Every structure of the body is made of chemicals and every function is related to chemical

interactions. Therefore this chapter provides students with the essential chemical background

needed to understand the anatomy and physiology of the body. Among the topics considered are

matter and energy, chemical elements, atomic structure, molecule formation, isotopes

(radioactive and stable forms), the role of electrons in chemical reactions, chemical bonds

(including ionic, covalent, and hydrogen bonds), forms of energy and chemical reactions, energy

transfer in chemical reactions, and the detailed mechanisms of chemical reactions (including

synthesis, decomposition, exchange, and reversible reactions). The importance of chemical

compounds in life processes is discussed, and the unique roles that inorganic and organic

compounds play in living systems are pointed out. The structure and significance of the

inorganic substances (water, acids, bases, and salts) are emphasized. Properties of carbon-based

molecules are explained before introducing the major organic compounds: carbohydrates, lipids,

proteins, nucleic acids (deoxyribonucleic acid, or DNA, and ribonucleic acid, or RNA), and

adenosine triphosphate (ATP). The concept of pH and the role of buffer systems and enzymes in

maintaining homeostasis are also explored. Clinical applications include the use of radioisotopes

in medical imagining, free radicals and their effects on health, galactosemia, and DNA

fingerprinting.




Chapter Outline and Objectives
INTRODUCTION

    1. Consider how atoms bond together in the body to form molecules.

    2. Discover how atoms and molecules release or store energy in processes known as

         chemical reactions.

    3. Discover how water is involved in nearly every chemical reaction.

    4. Define matter and mass.

HOW MATTER IS ORGANIZED

    Chemical Elements

    4. Identify the principal chemical elements of the human body by their names and

         chemical symbols.

    Structure of Atoms

    5. Describe each component of an atom in terms of its relative position, charge, and

         mass.

    Atomic Number and Mass Number

    6. Explain how the atomic number of an atom determines its chemistry because of the

         amount of attraction by the set number of nuclear positive charges for negative

         electrons of other atoms.

    7. Explain how mass number is related to radioisotopes and atomic weight.

    8. Give examples of some beneficial and harmful effects of radiation.

    Atomic Mass

    9.    Describe the standard unit for measuring the mass of atoms and their subatomic

         particles.
    10. Explain why an element‟s atomic weight can be slightly less than the mass number of

       its smallest stable isotope.

    Ions, Molecules, Free Radicals, and Compounds

    11. Distinguish among ions, molecules, free radicals, and compounds.

    12. Describe the effects of free radicals on health.

CHEMICAL BONDS

    13. Describe the significance of the valence shell electrons.

    14. Explain the octet rule.

    Ionic Bonds

    15. Explain why and how an atom can lose or gain electrons, and what the resulting

       balance between numbers of electrons and protons produces, as with sodium and

       chlorine.

    16. Note that when the attraction for electrons (electronegativity) between adjacent atoms

       is very different, one will pull electrons from the other, which produces oppositely

       charged ions that are attracted to each other and thus form an ionic bond.

    17. Describe what happens to most ionic molecules when put into water.

    Covalent Bonds

    18. Note that when atoms have a more similar attraction for external electrons, they share

       pairs of electrons (one from each atom) to form each single bond until all atoms in a

       molecule effectively fill their outer shells.

    19. Distinguish among single, double, and triple covalent bonds.

    20. Describe what happens to the distribution of electrons and charge in a covalent bond

       when the atoms have slightly different attractions for the electrons, as with carbon
       and oxygen, or in water molecules (distinguish between nonpolar covalent and polar

       covalent bonds).

    Hydrogen Bonds

    21. Describe the strength of the bond formed when a hydrogen atom covalently bound to

       one atom is also strongly attracted to an atom on a nearby molecule.

    22. Describe the effect on the overall shape of a large molecule due to a great number of

       hydrogen bonds between different parts of that molecule.

    23. Explain how hydrogen bonds result in the cohesion of water molecules and how this

       cohesion creates a high surface tension which is very important to the body.

CHEMICAL REACTIONS

    24. Define a chemical reaction.

    25. Explain the law of conservation of mass.

    Forms of Energy and Chemical Reactions

    26. Define energy and distinguish between potential and kinetic energy.

    27. Discuss chemical energy and explain the law of conservation of energy.

    Energy Transfer in Chemical Reactions

    28. Compare and contrast exergonic and endergonic reactions.

    29. Explain how activation energy is required to produce a chemical reaction and how

       concentration and temperature influence the rate of reaction.

    Catalysts

    30. Describe the role of catalysts in chemical reactions.

    Types of Chemical Reactions

    Synthesis Reactions - Anabolism
    31. Give an example of synthetic reactions that occur in the body and note that they

       usually require energy from a molecule called ATP.

    Decomposition Reactions - Catabolism

    32. Emphasize that catabolic reactions are used to obtain energy from food that is stored

       in a molecule called ATP.

    Exchange Reactions

    33. Describe what is meant by an exchange reaction.

    Reversible Reactions

    34. Note that most chemical reactions in the body are reversible because they are

       performed by special molecules called enzymes.

INORGANIC COMPOUNDS AND SOLUTIONS

    35. Distinguish between inorganic and organic compounds.

     Water

    36. Explain the importance of water in living systems.

    Water as a Solvent

    37. Explain the properties of water that make it an excellent solvent.

    Water in Chemical Reactions

    38. Distinguish between hydrolysis and dehydration synthesis.

    High Heat Capacity of Water

    39. Explain the reason for the high heat capacity of water.

    40. Discuss the high heat of vaporization of water.

    Cohesion of Water Molecules
    41. Explain how the cohesion of water molecules creates a high surface tension and what

       that means to the body.

    Water as a Lubricant

    42. Describe the lubricating effects of water in the body.

    Solutions, Colloids, and Suspensions

    43. Distinguish among mixtures, solutions, colloids, and suspensions.

    44. Explain the terms used to designate the constituents of a solution.

    45. Describe how solutions are expressed by percent and in units of moles per liter.

    Inorganic Acids, Bases, and Salts

    46. Indicate the general properties of acids, bases, and salts, as well as how they are

       related in chemical reactions.

    Acid-Base Balance: The Concept of pH

    47. Define pH in terms of hydrogen and base (hydroxide) ion concentration relative to

       water.

    Maintaining pH: Buffer Systems

    48. Define a buffer in terms of its ability to prevent large changes in [H+] due to strong

       acids and bases, in addition to the general mechanism.

    49. Use carbonic acid as an example of the response of a buffer to the addition of H+ or

       base (OH-) to show the overall [H+] does not change.



ORGANIC COMPOUNDS

    Carbon and Its Functional Groups

    50. List the properties of carbon that make it particularly useful to living organisms.
51. Describe the functional groups of organic compounds.

52. Discuss the fact that many organic molecules are macromolecules which are

   polymers formed by linking together monomers.

Carbohydrates

53. List the major forms of carbohydrates (sugars, starches, glycogen, and cellulose), and

   describe their functions.

54. Discuss the general rule for carbohydrates in that there is one carbon atom for each

   water molecule.

Monosaccharides and Disaccharides: The Simple Sugars

55. Discuss what is meant by a simple sugar.

56. Discuss how a disaccharide is formed.

Polysaccharides

57. Discuss the role of glycogen in the body.

Lipids

58. Discuss the chemical makeup and properties of lipids.

Triglycerides

59. Discuss the properties of triglycerides.

60. Distinguish among saturated, monounsaturated, and polyunsaturated fats.

Phospholipids

61. Describe the structure of phosphlipids.

Steroids

62. Describe the structure of steroids.

63. Discuss the role of cholesterol in steroid functioning.
64. Discuss the role of saturated fats and cholesterol in atherosclerosis

Other Lipids

65. Describe the structure and function of eicosanoids.

66. List other types of lipids.

Proteins

67. List and discuss the functional protein groups in the body.

Amino Acids and Polypeptides

68. Describe the basic amino acid structure and how amino acids are joined to form

    polypeptides.

Levels of Structural Organization in Proteins

69. Describe how a chain of amino acids interacts with itself to produce the four levels of

    structural organization and provide examples of where these are seen in anatomy.

Enzymes

70. Discuss the naming of enzymes.

71. Describe the properties of enzymes.

72. Describe the general operation of enzymes in terms of catalysis and the conditions

    needed to execute essential chemical reactions of metabolism.

73. Discuss galactosemia in terms of enzyme activity.

Nucleic Acids: Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA)

74. Note the two general types of nucleic acids and their role in heredity and protein

    production.

75. Discuss the structure of the four nitrogen bases and their interaction in the structure of

    the double helix.
       76. Discuss the technique of DNA fingerprinting.

       77. Discuss the differences between DNA and RNA.

       Adenosine Triphosphate

       78. Discuss the structure and function of ATP.

       79. Briefly discuss the phases of cellular respiration.

What’s New and Different In This Chapter

The discussions of ionic acids, bases and salts and solutions, colloids and suspensions are now

considered after the discussion of water. The discussion of oxidation/reduction reactions has

been eliminated. The figure which explains the level of structural organization in proteins has

been reworked and simplified.

Suggested Lecture Outline

I. INTRODUCTION

       A. Since chemicals compose your body and all body activities are chemical in nature, it

           is important to become familiar with the language and fundamental concepts of

           chemistry.

       B. Basic Principles

               1. Chemistry is the science of the structure and interactions of matter.

               2. Matter is anything that occupies space and has mass.

               3. Mass is the amount of matter a substance contains; weight is the force of

                  gravity acting on a mass.

II. HOW MATTER IS ORGANIZED

       A. Chemical Elements
      1. All forms of matter are composed of chemical elements which are substances

          that cannot be split into simpler substances by ordinary chemical means.

      2. Elements are given letter abbreviations called chemical symbols.

      3. Oxygen (O), carbon (C), hydrogen (H), and nitrogen (N) make up 96% of

          body weight. These elements, together with calcium (Ca) and phosphorus (P)

          make up 98.5% of total body weight.

      4. Table 2.1 lists the major and trace elements of the human body.

B. Structure of Atoms

      1. Units of matter of all chemical elements are called atoms. An element is a

          quantity of matter composed of atoms of the same type.

      2. Atoms consist of a nucleus, which contains positively charged protons and

          neutral (uncharged) neutrons, and negatively charged electrons that move

          about the nucleus in energy levels (Figure 2.1).

      3. Electrons revolve around the nucleus of an atom tending to spend most of the

          time in specific atomic regions, called shells (Figure 2.1b).

             a. Each shell can hold a certain maximum number of electrons.

             b. The first shell, the one nearest the nucleus, can hold a maximum of 2

                 electrons; the second shell, 8; the third shell;18,the fourth shell, 18;

                 and so on (Figure 2.2).

      4. The number of electrons in an atom of a neutral element always equals the

          number of protons.

C. Atomic Number and Mass Number

      1. The number of protons in the nucleus of an atom
             a. The number of protons in the nucleus makes the atoms of one element

                 different from those of another as illustrated in Figure 2.2.

             b. Since all atoms are electrically neutral, the atomic number also equals

                 the number of electrons in each atom.

      2. The mass number of an atom is the total number of protons and neutrons.

      3. Different atoms of an element that have the same number of protons but

          different numbers of neutrons are called isotopes.

             a. Stable isotopes do not change their nuclear structure over time.

             b. Certain isotopes called radioactive isotopes are unstable because their

                 nuclei decay to form a simpler and thus more stable configuration.

             c. Radioactive isotopes can be used to study both the structure and

                 function of particular tissues as described in the Clinical Application

                 on “Harmful and Beneficial Effects of Radiation.”

D. Atomic Mass

      1. The atomic mass, also called the atomic weight, of an element is the average

          mass of all its naturally occurring isotopes and reflects the relative abundance

          of isotopes with different mass numbers.

      2. The mass of a single atom is slightly less than the sum of the masses of its

          neutrons, protons, and electrons because some mass (less than1%) was lost

          when the atom‟s components came together to form an atom.

E. Ions, Molecules, Free Radicals, and Compounds
            1. If an atom either gives up or gains electrons, it becomes an ion - an atom that

                 has a positive or negative charge due to having unequal numbers of protons

                 and electrons.

            2. When two or more atoms share electrons, the resulting combination is called a

                 molecule (Figure 2.3a).

            3. A free radical is an electrically charged atom or group of atoms with an

                 unpaired electron in its outermost shell (Figure 2.3b).

                    a. Free radicals become stable by either giving up their unpaired electron

                        or by taking on an electron from another molecule.

                    b. Antioxidants are substances that inactivate oxygen-derived free

                        radicals.

            4. A compound is a substance that can be broken down into two or more

                 different elements by ordinary chemical means.

            5. Free radicals are linked to numerous disorders and diseases as described in the

                 Clinical Application on “Free Radicals and Their Effects on Health.”

III. CHEMICAL BONDS

     A. The atoms of a molecule are held together by forces of attraction called chemical

        bonds.

            1. The likelihood that an atom will form a chemical bond with another atom

                 depends on the number of electrons in its outermost shell, also called the

                 valence shell.
      2. An atom with a valence shell holding eight electrons (2 electrons for hydrogen

         and neon) is chemically stable, which means it is unlikely to form chemical

         bonds with other atoms.

      3. To achieve stability, atoms that do not have eight electrons in their valence

         shell (or 2 in the case of H and He) tend to empty their valence shell or fill it

         to the maximum extent.

      4. Atoms with incompletely filled outer shells tend to combine with each other in

         chemical reactions to produce a chemically stable arrangement of eight

         valence electrons for each atom. This chemical principle is called the octet

         rule.

B. Ionic Bonds

      1. When an atom loses or gains a valence electron, ions are formed (Figure 2.4).

             a. Positively and negatively charged ions are attracted to one another.

             b. When this force of attraction holds ions having opposite charges

                 together, an ionic bond results.

      2. Cations are positively charged ions that have given up one or more electrons

         (they are electron donors).

      3. Anions are negatively charged ions that have picked up one or more electrons

         that another atom has lost (they are electron acceptors).

      4. In general, ionic compounds exist as solids but some may dissociate into

         positive and negative ions in solution. Such a compound is called an

         electrolyte.
      5. Table 2.2 lists the names and symbols of the most common ions and ionic

         compounds in the body.

C. Covalent Bonds

      1. Covalent bonds are formed by the atoms of molecules sharing one, two, or

         three pairs of their valence electrons.

      2. Covalent bonds are the most common chemical bonds in the body.

      3. Single, double, or triple covalent bonds are formed by sharing one,two, or

         three pairs of electrons, respectively (Figure 2.5).

      4. Covalent bonds may be nonpolar or polar.

             a. In a nonpolar covalent bond, atoms share the electrons equally;one

                 atom does not attract the shared electrons more strongly than the other

                 atom (Figure 2.5).

             b. In a polar covalent bond, the sharing of electrons between atoms is

                 unequal; one atom attracts the shared electrons more strongly than the

                 other (Figure 2.6).

D. Hydrogen Bonds

      1. In a hydrogen bond, two other atoms (usually oxygen or nitrogen) associate

         with a hydrogen atom (Figure 2.7).

      2. Hydrogen bonds are weak and cannot bind atoms into molecules. They serve

         as links between molecules.

      3. They provide strength and stability and help determine the three- dimensional

         shape of large molecules.
          4. Hydrogen bonds linking neighboring water molecules (Figure 2.7) give water

              considerable cohesion which creates a very high surface tension.

IV. CHEMICAL REACTIONS

    A. A chemical reaction occurs when new bonds are formed or old bonds break between

       atoms (Figure 2.8).

          1. The starting substances of a chemical reaction are known as reactants.

          2. The ending substances of a chemical reaction are the products.

          3. In a chemical reaction, the total mass of the reactants equals the total mass of

              the products (the law of conservation of mass).

          4. Metabolism refers to all the chemical reactions occurring in an organism.

    B. Forms of Energy and Chemical Reactions

          1. Energy is the capacity to do work.

                  a. Potential energy is energy stored by matter due to its position.

                  b. Kinetic energy is the energy associated with matter in motion.

                  c. Chemical energy is a form of potential energy stored in the bonds of

                        compounds or molecules.

          2. The total amount of energy present at the beginning and end of a chemical

              reaction is the same; energy can neither be created nor destroyed although it

              may be converted from one form to another (law of conservation of energy).

    C. Energy Transfer in Chemical Reactions

          1. Breaking chemical bonds requires energy and forming new bonds releases

              energy.
             a. An exergonic reaction is one in which the bond being broken has more

                 energy than the one formed so that extra energy is released, usually as

                 heat (occurs during catabolism of food molecules).

             b. An endergonic reaction is just the opposite and thus requires energy,

                 usually from a molecule called ATP, to form a bond, as in bonding

                 amino acid molecules together to form proteins

      2. Activation energy is the collision energy needed to break chemical bonds in

          the reactants (Figure 2.9).

             a. This is the initial energy needed to start a reaction.

             b. Factors that influence the chance that a collision will occur and cause a

                 chemical reaction include

                     1) Concentration

                     2) Temperature.

      3. Catalysts are chemical compounds that speed up chemical reactions by

          lowering the activation energy needed for a reaction to occur (Figure 2.10).

             a. A catalyst does not alter the difference in potential energy between the

                 reactants and products. It only lowers the amount of energy needed to

                 get the reaction started.

             b. A catalyst helps to properly orient the colliding particles of matter so

                 that a reaction can occur.

             c. The catalyst itself is unchanged at the end of the reaction.

D. Types of Chemical Reactions
           1. Synthesis reactions occur when two or more atoms, ions, or molecules

               combine to form new and larger molecules. These are anabolic reactions,

               meaning that bonds are formed.

           2. In a decomposition reaction, a molecule is broken down into smaller parts.

               These are catabolic reactions, meaning that chemical bonds are broken in the

               process.

           3. Exchange reactions involve the replacement of one atom or atoms by another

               atom or atoms.

           4. In reversible reactions, end products can revert to the original combining

               molecules.

V. INORGANIC COMPOUNDS AND SOLUTIONS

    A. Inorganic compounds usually lack carbon and are simple molecules; whereas organic

       compounds always contain carbon and hydrogen, usually contain oxygen, and always

       have covalent bonds.

    B. Water

           1. Water is the most important and abundant inorganic compound in all living

               systems.

                  a. The most important property of water is its polarity, the uneven

                      sharing of valence electrons that confers a partial negative charge near

                      the one oxygen atom and two partial positive charges near the two

                      hydrogen atoms in the water molecule (Figure 2.7).

                  b. Water enables reactants to collide to form products.

           2. Water as a solvent
       a. In a solution the solvent dissolves the solute.

       b. The polarity of water and its bent shape allow it to interact with

          several neighboring ions or molecules.(Figure 2.11)

       c. Substances which contain polar covalent bonds and dissolve in water

          are hydrophilic, while substances which contain non polar covalent

          bonds are hydrophobic.

       d. Water‟s role as a solvent makes it essential for health and survival.

3. Water in Chemical Reactions

       a. Water is the ideal medium for most chemical reactions in the body

          and participates as a reactant or product in certain reactions.

       b. Hydrolysis breaks large molecules down into simpler ones by adding a

          molecule of water.

       c. Dehydration synthesis occurs when two simple molecules join

          together, eliminating a molecule of water in the process.

4. High Heat Capacity of Water

       a. Water has a high heat capacity.

              1) It can absorb or release a relatively large amount of heat with

                  only a modest change in its own temperature.

              2) This property is due to the large number of hydrogen ions in

                  water.

       b. Water has a high heat of vaporization. It requires a large amount of

          heat to change from a liquid to a gas.

5. Water as a Lubricant
              a. Water is a major part of mucus and other lubricating fluids.

              b. It is found wherever friction needs to be reduced or eliminated

C. Solutions, Colloids, and Suspensions

       1. A mixture is a combination of elements or compounds that are physically

          blended together but are not bound by chemical bonds. Three common liquid

          mixtures are solutions, colloids, and suspensions.

              a. In a solution, a substance called the solvent dissolves another

                  substance called the solute. Usually there is more solvent than solute in

                  a solution.

              b. A colloid differs from a solution mainly on the basis of the size of its

                  particles with the particles in the colloid being large enough to scatter

                  light.

              c. In a suspension, the suspended material may mix with the liquid or

                  suspending medium for some time, but it will eventually settle out.

       2. The concentration of a molecule is a way of stating the amount of that

          molecule dissolved in solution (Table 2.3).

              a. Percent gives the relative mass of a solute found in a given volume of

                  solution.

              b. A mole is the name for the number of atoms in an atomic weight of

                  that element, or the number of molecules in a molecular weight of that

                  type of molecule, with the molecular weight being the sum of all the

                  atomic weights of the atoms that make up the molecule.

D. Inorganic Acids, Bases, and Salts
      1. When molecules of inorganic acids, bases, or salts dissolve in water, they

          undergo ionization or dissociation; that is, they separate into ions.

      2. Acids ionize into one or more hydrogen ions (H+) and one or more anions

          (negative ions) (Figure 2.12a).

      3. Bases dissociate into one or more hydroxide ions (OH-) and one or more

          cations (positive ions) and are proton acceptors (Figure 2.12b).

      4. A salt, when dissolved in water, dissociates into cations and anions, neither of

          which is H+ or OH- (Figure 2.12c). Many salts are present in the body and are

          formed when acids and bases react with each other.

E. Acid-Base Balance: The Concept of pH

      1. Body fluids must constantly contain balanced quantities of acids and bases.

      2. Biochemical reactions are very sensitive to even small changes in acidity or

          alkalinity.

      3. A solution‟s acidity or alkalinity is based on the pH scale, which runs from )

          (=100 = 1.0 moles H+/L) to 14 (= 10-14 = 0.00000000000001 moles H+/L)

          (Figure 2.13)

              a. pH 7.0 = 10-7 = 0.0000001 moles H+/L = neutrality or equal numbers

                  of [H+] and [OH-].

              b. Values below 7 indicate acid solutions ([H+] > [OH-]).

              c. Values above 7 indicate alkaline solutions ([H+] < [OH-]).

F. Maintaining pH: Buffer Systems

      1. The pH values of different parts of the body are maintained fairly constant by

          buffer systems, which usually consist of a weak acid and a weak base.
          2. The function of a buffer system is to convert strong acids or bases into weak

              acids or bases.

          3. One important buffer system in the body is the carbonic acid-bicarbonate

              buffer system.

                 a. Bicarbonate ions (HCO3-) act as weak bases and carbonic acid

                     (H2CO3) acts as a weak acid.

                 b. CO2 + H2O  H2CO3  H+ + HCO3-

          4. Table 2.4 shows pH values for certain body fluids compared to common

              substances.

VI. ORGANIC COMPOUNDS

    A. Carbon and Its Functional Groups

          1. The carbon that organic compounds always contain has several properties

              that make it particularly useful to living organisms.

                 a. It can react with one to several hundred other carbon atoms to form

                     large molecules of many different shapes.

                 b. Many carbon compounds do not dissolve easily in water, making them

                     useful materials for building body structures.

                 c. Carbon compounds are mostly or entirely held together by covalent

                     bonds and tend to decompose easily; this means that organic

                     compounds are a good source of energy.

                 d. The chain of carbon atoms in an organic molecule is the carbon

                     skeleton. Attached to the carbon skeleton are distinctive functional
                   groups, in which other elements form bonds with carbon and hydrogen

                   atoms.

                      1) Each types of functional group has a specific arrangement of

                            atoms that confers characteristic chemical properties upon

                            organic molecules.

                      2) Table 2.5 lists the most common functional groups.

                      3) Fig 2.14 shows two ways to indicate the structure of the sugar

                            glucose.

      2. Small organic molecules can combine to form very large molecules

         (macromolecules, or polymers, when composed of repeating units called

         monomers).

             a. When two monomers joint together, the reaction is usually dehydration

                   synthesis.

             b. Macromolecules break down into monomers usually by hydrolysis.

      3. Molecules that have the same molecular formula but different structures are

         called isomers.

B. Carbohydrates

      1. Carbohydrates provide most of the energy needed for life and include sugars,

         starches, glycogen, and cellulose.

             a. Some carbohydrates are converted to other substances which are used

                   to build structures and to generate ATP.

             b. Other carbohydrates function as food reserves.
               c. The general structural rule for carbohydrates is one carbon atom for

                   each water molecule (CH2O).

               d. Carbohydrates are divided into three major groups based on their size:

                   monosaccharides, disaccharides, and polysaccharides (Table 2.6).

      2. Monosaccharides and Disaccharides: The Simple Sugars

               a. Monosaccharides contain from three to seven carbon atoms and

                   include glucose, a hexose that is the main energy-supplying compound

                   of the body.

               b. Disaccharides are formed from two monosaccharides by dehydration

                   synthesis; they can be split back into simple sugars by hydrolysis

                   (Figure 2.15). Glucose and fructose combine, for example, to produce

                   sucrose.

      3. Polysaccharides

               a. Polysaccharides are the largest carbohydrates and may contain

                   hundreds of monosaccharides.

               b. The principal polysaccharide in the human body is glycogen, which is

                   stored in the liver or skeletal muscles. (Figure 2.16)

C. Lipids

      1. Lipids, like carbohydrates, contain carbon, hydrogen, and oxygen; but unlike

            carbohydrates, they do not have a 2:1 ratio of hydrogen to oxygen.

               a. They have fewer polar covalent bonds and thus are mostly insoluble in

                   polar solvents such as water (they are hydrophobic).
       b. Table 2.7 summarizes the various types of lipids and highlights their

          roles in the human body.

2. Triglycerides

       a. Triglycerides are the most plentiful lipids in the body and provide

          protection, insulation, and energy (both immediate and stored).

              1) At room temperature, triglycerides may be either solid (fats) or

                   liquid (oils).

              2) Triglycerides provide more than twice as much energy per

                   gram as either carbohydrates or proteins.

              3) Triglyceride storage is virtually unlimited.

              4) Excess dietary carbohydrates, proteins, fats, and oils will be

                   deposited in adipose tissue as triglycerides.

       b. Triglycerides are composed of glycerol and fatty acids (Figure 2.17).

       c. The type of covalent bonds (and by inference, number of hydrogen

           atoms) found in the fatty acids determines whether a triglyceride is

           saturated, monounsaturated, or polyunsaturated.

3. Phospholipids

       a. Phospholipids are important membrane components.

       b. They are amphipathic, with both polar and nonpolar regions (Figure

          2.18).

4. Steroids

       a. Steroids have four rings of carbon atoms (Figure 2.19).
              b. Steroids include sex hormones and cholesterol, with cholesterol

                  serving as an important component of cell membranes and as starting

                  material for synthesizing other steroids.

      5. Other Lipids

              a. Eicosanoids include prostaglandins and leukotrienes.

                     1) Prostaglandins modify responses to hormones, contribute to

                           inflammatory responses, prevent stomach ulcers, dilate airways

                           to the lungs, regulate body temperature, and influence blood

                           clots, among other things.

                     2) Leukotrienes participate in allergic and inflammatory

                           responses.

              b. Body lipids also include fatty acids; fat-soluble vitamins such as beta-

                  carotenes, vitamins D, E, and K; and lipoproteins.

D. Proteins

      1. Proteins give structure to the body, regulate processes, provide protection,

          help muscles to contract, transport substances, and serve as enzymes (Table

          2.8).

      2. Amino Acids and Polypeptides

              a. Proteins are constructed from combinations of amino acids.

              b. Amino acids contain carbon, hydrogen, oxygen and nitrogen (Figure

                  2.20).
       c. Amino acids are joined together in a stepwise fashion with each

          covalent bond joining one amino acid to the next forming a bond

          called a peptide bond (Figure 2.21).

       d. Resulting polypeptide chains may contain 10 to more than 2,000

          amino acids.

3. Levels of Structural Organization

       a. Levels of structural organization include primary, secondary, tertiary,

          and quaternary structures (Figure 2.22).

       b. The resulting shape of the protein greatly influences its ability to

          recognize and bind to other molecules.

       c. Denaturation of a protein by a hostile environment causes loss of its

          characteristic shape and function.

4. Enzymes

       a. Catalysts in living cells are called enzymes.

       b. The names of enzymes usually end in the suffix -ase; oxidase, kinase,

          and lipase, are examples.

       c. Although enzymes catalyze select reactions, they do so with great

          efficiency and with many built-in controls.

              1) Enzymes are highly specific in terms of the substrate with

                  which they react.

              2) Enzymes are extremely efficient in terms of the number of

                  substrate molecules with which they react.

              3) Enzymes are subject to a great deal of cellular controls.
             d. Enzymes speed up chemical reactions by increasing frequency of

                  collisions, lowering the activation energy and properly orienting the

                  colliding molecules (Figure 2.23).

             e. The lack of a particular enzyme is found in the inherited disorder

                  galactosemia, which is described in a Clinical Application.

E. Nucleic Acids: Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA)

      1. Nucleic acids are huge organic molecules that contain carbon, hydrogen,

          oxygen, nitrogen, and phosphorus.

             a. Deoxyribonucleic acid (DNA) forms the genetic code inside each cell

                  and thereby regulates most of the activities that take place in our cells

                  throughout a lifetime.

             b. Ribonucleic acid (RNA) relays instructions from the genes in the cell‟s

                  nucleus to guide each cell‟s assembly of amino acids into proteins by

                  the ribosomes.

      2. The basic units of nucleic acids are nucleotides, composed of a nitrogenous

          base, a pentose, sugar, and a phosphate group (Figure 2.24).

      3. DNA fingerprinting is used in research and in legal situations to determine the

          genetic identify of an individual. This technique is discussed in a Clinical

          Application box.

F. Adenosine Triphosphate

      1. Adenosine triphosphate (ATP) is the principal energy-storing molecule in the

          body.
                2. Among the cellular activities for which ATP provides energy are muscular

                    contractions, chromosome movement during cell division, cytoplasmic

                    movement within cells, membrane transport processes, and synthesis

                    reactions.

                3. ATP consists of three phosphate groups attached to an adenosine unit

                    composed of adenine and the five-carbon sugar ribose (Figure 2.25).

                       a. When energy is liberated from ATP, it is decomposed to adenosine

                           diphosphate (ADP) and phosphorus (P).

                       b. ATP is manufactured from ADP and P using the energy supplied by

                           various decomposition reactions, particularly that of glucose.



Teaching Tips

   Students often have difficulty visualizing the structures of chemicals and the mechanisms of

    their reactions. Try using models (available from Carolina, Ward‟s or

    major biological supply houses) to demonstrate atomic structure, formation of

    molecules, and the different types of chemical bonds. Also use models or diagrams

    to illustrate the structural differences between inorganic and organic compounds to

    distinguish the proteins from carbohydrates and lipids, pointing out the secondary,

    tertiary, and quaternary configurations of protein molecules and their functional

    significance.

   Various multimedia resources are available for demonstrating chemical structure.



Critical Thinking Questions
1. Buffer systems are vital chemicals that help to maintain the pH of body fluids. Using

   the carbonic acid-bicarbonate buffer pair as an example, explain how the buffer

   operates to counteract a strong acid or a strong base.

2. Compare the diagrams of the chemical structures of the two major categories of energy-

   providing molecules in our food: carbohydrates and lipids. What is it about the structure of

   lipids that causes them to contain so many more calories than an equivalent volume of

   carbohydrates?



Educational Resources (refer to Educational Resources Appropriate for All Chapters

       following the list of Suppliers and Distributors).

Videocassettes

Basic Chemistry for Biology Students (30 min; 1993; HRM) - introduces chemical

       concepts basic to understanding life processes

Chemistry and Biology (MBV) - examines atoms, molecules, isotopes, and organic and

       inorganic chemistry

Infinite Voyage: The Geometry of Life (60 min; 1990; FSE) - explores DNA to decipher

       its code

The Molecular Building Blocks of Life (18 min; CVB) - studies carbon chemistry,

       polymers, carbohydrates, proteins, nucleic acids, energy storage, fats, and enzymes

Free Radicals (30 min; FHS - explains how free radicals are created; how they; their

       effect on the body

Physiological Concepts of Life Sciences (1993; WCB) - covers many topics including

       enzyme action
Proteins (34 min; FHS) - covers protein structure and function



Computer Resources (CD-ROMs for Windows and Macintosh platforms unless otherwise

       noted)

Biochemistry: Part I (SVE) - covers the chemistry of life, carbohydrates and lipids,

       proteins, and nucleic acids

Biochemistry: Part II (SVE) - covers buffers, proteins synthesis, and enzymes

Biochemistry: The Chemistry of Living Things (CEI) - explores atoms, elements,

       molecules, and the chemical compounds of life; interactive tutorials

The Chemistry of Life (1998; BC) - ilustrates crucial chemical concepts needed for every

       life science course; interactive

DNA: The Master Molecule (BIO) - discusses building DNA from sugars and phosphates,

       transcription of mRNA, amino acid codes, protein synthesis; interactive

DNA: The Molecule of Life (SVE) - examines the chemical makeup of DNA, the

       structure and replication of DNA, and more

Enzymes (1996; FREY) - a basic study of enzyme action



Selected Readings

Darnell, J. E. “RNA,” Scientific American (October 1985)

Doolittle, R. F. “Proteins,” Scientific American (October 1985)

Felsenfeld, G. “DNA,” Scientific American (October 1985)

Frieden, E. “The Chemical Elements of Life,” Scientific American (July 1972)

Karpus, M., and J. A. McCammon. “The Dynamics of Proteins,” Scientific American
       (April 1986)

Moxon, E. R., and C. Wills. “DNA Microsatellites: Agents of Evolution?” Scientific

       American (January 1999)

Sharon, N. “Carbohydrates,” Scientific American (November 1980)

Weinberg, R. A. “The Molecular Basis of Life,” Scientific American (October 1985)

Weinberg, R. A. “The Molecules of Life,” Scientific American (October 1985)
Chapter 3

THE CELLULAR LEVEL OF ORGANIZATION

Chapter Synopsis

Students are presented with the structural and functional aspects of cells through analysis of a

generalized animal cell. The cell is divided into three principal parts for ease of study: the plasma

membrane, the cytoplasm consisting of the cytosol and organelles, and the nucleus. The anatomy

and physiology of the plasma membrane is covered in extensive detail. Consideration is given to

important processes of movement of materials across the plasma membrane, including diffusion,

osmosis, diffusion through the lipid bilayer, diffusion through membrane channels, facilitated

diffusion, active transport, and vescicular transport (endocytosis including receptor mediated

endocytosis, phagocytosis and pinocytosis, and exocytosis). The form and function of the

cytosol, organelles, and nucleus are similarly covered. Attention is also given to the events

involved in protein synthesis following the processes of transcription of DNA to mRNA and

translation of mRNA to the creation of a protein. The result, mechanisms, and importance of

somatic - mitotic cell division are examined thoroughly. The chapter concludes with a discussion

of the effects of aging on cells and cellular diversity. Cancer is discussed as a homeostatic

imbalance exemplified by uncontrolled division of cells. The subject of cancer is explored in

several areas: growth and spread of malignant tumors, types of cancers, causes, the multistep

process of carcinogenesis, and treatment. Clinical applications that are covered include the

mechanism by which cholesterol modifies membrane fluidity, the mechanism by which digitalis

affects the sodium pump in heart muscle, the cellular basis of cystic fibrosis, the cellular basis of

Tay-Sachs disease, recombinant DNA, and abnormalities in genes that help to regulate the cell

cycle and the problems they cause.
Chapter Outline and Objectives

INTRODUCTION

      1. Define a cell

      2. Describe the connection between the chemical level of organization and cellular

         components.

      3. Relate the essential importance of the cellular level of organization to all life forms.

PARTS OF A CELL

      4. Describe the three principal parts of a cell.

THE PLASMA MEMBRANE

      5. Describe how the “fluid mosaic model” concept appropriately describes the nature

         and structure of the plasma membrane.

      The Lipid Bilayer

      6. Explain how the chemical nature of the distinct regions of phospholipids

         automatically produces a lipid bilayer in a water solution, with a range of properties.

      7. Describe the function of cholesterol and glycolipids in membranes.

      Arrangement of Membrane Proteins

      8. Distinguish between integral and peripheral proteins in cell membranes.

      Functions of Membrane Proteins

      9. Describe the chemistry and function of membrane proteins.

      Membrane Fluidity

      10. Discuss the fluidity of membranes and the mobility of membrane lipids and proteins.

      11. Explain how cholesterol modifies membrane fluidity.
    Membrane Permeability

    12. Explain the mechanisms and factors involved in the selective movement of materials

       across the cell membrane.

    Gradients Across the Plasma Membrane

    13. Define a chemical and electrical gradient and the predominant ions involved on

       opposite sides of the plasma membrane.

    14. Explain how an electrical gradient leads to the membrane potential that exists in cells

       of the body.

TRANSPORT ACROSS THE PLASMA MEMBRANE

    15. Distinguish between passive and active transport, including direction of particle

       movement and energy requirements.

    16. Distinguish between nonmediated and mediated transport.

    17. Discuss the role of transporter proteins in mediated transport.

    18. Discuss the basis of vesicular transport.

    Principles of Diffusion

    19. Explain the concept of diffusion based on the kinetic energy of random motion in

       terms of concentration differences, net movement, and the properties of substances

       and conditions.

    20. List and explain the factors that influence the diffusion rate of substances in solution.

    Osmosis

    21. Explain the process of osmosis as the net movement of a solvent through a selectively

       permeable membrane.

    22. Discuss the roles of hydrostatic pressure and osmotic pressure in regulating osmosis.
    23. Show the relation of osmotic pressure to tonicity by the effect on red blood cells of

       different concentrations of solute in a surrounding solution.

    Diffusion Through the Lipid Bilayer

    24. Describe the movement of nonpolar, hydrophobic molecules through the lipid bilayer

       of the plasma membrane.

    Diffusion Through Membrane Channels

    25. Describe the process of small, inorganic ion movement across the plasma membrane.

    Facilitated Diffusion

    26. Detail the facilitated diffusion characteristics and process where transporter proteins

       move glucose molecules along their concentration gradients.

    Active Transport

    27. Define active transport and list two energy sources used to drive the process.

    Primary Active Transport

    28. Describe the process of primary active transport and relate it to the sodium pump.

    Secondary Active Transport

    29. Describe the process of secondary active transport and the role of symporters and

       antiporters.

    30. Discuss the effect of digitalis on the sodium pump.

TRANSPORT IN VESICLES

    31. Describe the two main types of vesicular transport between a cell and its extracellular

       fluid.

    Endocytosis

    32. Describe the process of endocytosis.
    Receptor-Mediated Endocytosis

    33. Define ligand and discuss its role in receptor mediated endocytosis.

    34. List and explain the steps involved in receptor-mediated endocytosis.

    35. Describe how some viruses can use receptor-mediated endocytosis to infect body

       cells.

    Phagocytosis

    36. Define phagocytosis and explain its importance.

    Pinocytosis

    37. Define pinocytosis and explain its importance.

    Exocytosis

    38. Describe the process of exocytosis.

CYTOPLASM

    39. List the two components of the cytoplasm.

    Cytosol

    40. Describe the elements of the cytosol and how it is different from the plasma

       membrane.

    Organelles

    41. Describe the basic structural features and functions of organelles.

    42. Distinguish between membranous and nonmembranous organelles.

    The Cytoskeleton

    43. Distinguish the characteristics and functions of microfilaments, microtubules, and

       intermediate filaments.
Centrosome

44. Show the relationship of cytoskeletal elements to centrioles and the centrosome and

   note their purpose in dividing and nondividing cells.

Cilia and Flagella

45. Describe the arrangement of microtubules in flagella and cilia that allow these

   projections to perform the different types of transport movements.

Ribosomes

46. Indicate the origin and components of ribosomes that allow them to produce proteins,

   and their association with other organelles in this process.

Endoplasmic Reticulum

47. Specify how the interconnected form of the ER membranous labyrinth is related to its

   various synthetic purposes and molecular distribution within the cell.

Golgi Complex

48. Describe how the Golgi apparatus conducts the processing and directing of newly

   synthesized molecules.

49. Convey how the faulty operation of the Golgi complex is related to cystic fibrosis.

Lysosomes

50. Delineate the role of lysosomal enzymes in protection, digestion, and recycling of

   external and internal substances.

51. Describe how faulty lysosomes are related to Tay-Sachs disease.

Peroxisomes

52. Describe the enzymes and reactants peroxisomes use to deactivate potentially toxic

   molecules.
     Mitochondria

     53. Indicate how the two membrane layers of the mitochondrion are associated with the

        enzymes that produce the energy-storage molecule ATP.

     54. Describe the role of DNA in mitochondrial replication.

NUCLEUS

     55. Discuss the morphology and function of the nuclear envelope, nucleoli, and

        hierarchical levels of chromatin.

PROTEIN SYNTHESIS

     56. Accentuate that DNA acts by coding for structural and functional (enzyme)

        proteins,and those proteins form all the structures and perform almost all the

        metabolic reactions to generate and maintain an organism.


Transcription
     57. Describe the steps of transcription and nucleotides of the DNA sequence that are used

        to synthesize complementary sequences of RNA nucleotides of three types.

     58. Define the process and functions of the gene splicing of mRNA.


Translation
     59. Provide the identity and function of all the molecules involved in the translation

        process.

     60. Illustrate the relation between the codes of the DNA nucleotide triplet, the mRNA

        codon, and the rRNA anticodon that specifies an amino acid in the protein sequence.

     61. Go through the steps in which the molecular components of this process interact to

        translate the mRNA sequence into a successive coupling of amino acids in a protein.

     62. Discuss the techniques of genetic engineering and recombinant DNA.
NORMAL CELL DIVISION

    63. Define cell division

    64. Distinguish between somatic and reproductive cell division.

    The Cell Cycle in Somatic Cells

    65. Describe the chromosome number in terms of homologous pairs and stress the

       importance of chromosome replication prior to cell division.

    Interphase

    66. Indicate the objectives and activities of the DNA and cell components in each phase

       of the interphase cell cycle.

    Mitotic Phase

    67. List the events of each phase of mitosis.

    Cytoplasmic Division: Cytokinesis

    68. Explain what is happening to the cytoplasm, organelles, and plasma membrane during

       cytokinesis, and why.

    Control of Cell Destiny

    69. List and describe the three possible destinies of a cell.

    70. Describe the role of tumor-suppressor genes in the cell cycle.

CELLS AND AGING

    71. . Explain how the three main theories of aging (genetic programming, free radical

       reactions, and excess immune response) lead to the signs of aging.

CELLULAR DIVERSITY

    72. Discuss the concept of cellular diversity.

DISORDERS: HOMEOSTATIC IMBALANCES
       73. . Describe cancer (CA) as a homeostatic imbalance of cells with different

           characteristics for benign versus malignant tumors.

       Types of Cancer

       74. Distinguish the origins and properties of the different types of tumors.

       Growth and Spread of Cancer

       75. Describe the effects of hyperplasia, metastasis, and secondary site development on

           normal tissue.

       Causes of Cancer

       76. Explain the nature of the numerous carcinogens and viruses and with which cell

           growth control genes they may interact.

       Carcinogenesis: A Multistep Process

       77. Describe the features and progression of steps that lead a normal cell to develop into a

           malignancy.

       Treatment of Cancer

       78. Discuss how it is that the multiple personalities of the cells within a tumor make the

           differing drug therapies difficult or ineffective.

MEDICAL TERMINOLOGY

       79. Define medical terminology associated with cells.




What’s New and Different In This Chapter

A discussion of the clinical applications of isotonic, hypotonic, and hypertonic solutions has

been added. The structure and function of proteasomes and their role in diseases is now

discussed. The topic of antisense therapy has been added.
Suggested Lecture Outline

I. INTRODUCTION

      A. A cell is the basic, living, structural, and functional unit of the body.

      B. Cytology is the study of cell structure, and cell physiology is the study of cell

          function.

II. PARTS of a CELL

      A. A generalized view of the cell is a composite of many different cells in the body as

          seen in Figure 3.1. No single cell includes all of the features seen in the generalized

          cell.

      B. The cell can be divided into three principal parts for ease of study.

              1. Plasma (cell) membrane

              2. Cytoplasm

                      a. Cytosol

                      b. Organelles (except for the nucleus)

              3. Nucleus

III. THE PLASMA MEMBRANE

       A. The plasma membrane is a flexible, sturdy barrier that surrounds and contains the

          cytoplasm of the cell.

              1. The fluid mosaic model describes its structure (Figure 3.2).

              2. The membrane consists of proteins in a sea of lipids.

      B. The Lipid Bilayer
      1. The lipid bilayer is the basic framework of the plasma membrane and is made

          up of three types of lipid molecules: phospholipids, cholesterol, and

          glycolipids (Figure 3.2).

      2. The bilayer arrangement occurs because the lipids are amphipathic moleeules.

          They have both polar (charged) and nonpolar (uncharged) parts with the polar

          “head” of the phospholipid pointing out and the nonpolar “tail” pointing

          toward the center of the membrane.

C. Arrangement of Membrane Proteins

      1. The membrane proteins are divided into integral and peripheral proteins.

             a. Integral proteins extend into or across the entire lipid bilayer among

                 the fatty acid tails of the phospholipid molecules.

             b. Peripheral proteins are found at the inner or outer surface of the

                 membrane and can be stripped away from the membrane without

                 disturbing membrane integrity.

      2. Integral membrane proteins are amphipathic.

             a. Those that stretch across the entire bilayer and project on both sides of

                 the membrane are termed transmembrane proteins.

             b. Many integral proteins are glycoproteins.

      3. The combined glycoproteins and glycolipids form the glycocalyx which helps

          cells recognize one another, adhere to one another, and be protected from

          digestion by enzymes in the extracellular fluid.

D. Functions of Membrane Proteins
      1. Membrane proteins vary in different cells and functions as channels (pores),

         transporters, receptors, enzymes, cell-identity markers, and linkers (Figure

         3.3).

      2. The different proteins help to determine many of the functions of the plasma

         membrane.

E. Membrane Fluidity

      1. Membranes are fluid structures, rather like cooking oil, because most of the

         membrane lipids and many of the membrane proteins easily move in the

         bilayer.

      2. Membrane lipids and proteins are mobile in their own half of the bilayer.

      3. Cholesterol serves to stabilize the membrane and reduce membrane fluidity.

F. Membrane Permeability

      1. Plasma membranes are selectively permeable, meaning that some things can

         pass through and others cannot.

      2. The lipid bilayer portion of the membrane is permeable to small, nonpolar,

         uncharged molecules but impermeable to ions and charged or polar molecules.

         It is also permeable to water..

      3. Transmembrane proteins that act as channels or transporters increase the

         permeability of the membrane to molecules that cannot cross the lipid bilayer.

      4. Macromolecules are unable to pass through the plasma membrane except by

         vesicular transport.

G. Gradients Across the Plasma Membrane
           1. A concentration gradient is the difference in the concentration of a chemical

               between one side of the plasma membrane and the other.

                   a. Oxygen and sodium ions are more concentrated outside the cell

                       membrane with carbon dioxide and potassium ions more concentrated

                       inside the cell membrane (Figure 3.4a).

                   b. The inner surface of the membrane is more negatively charged and the

                       outer surface is more positively charged (Figure 3.4b). This sets up an

                       electrical gradient, also called the membrane potential.

           2. Maintaining the concentration and electrical gradients are important to the life

               of the cell.

           3. The combined concentration and electrical gradients are called the

               electrochemical gradient.

IV. TRANSPORT ACROSS THE PLASMA MEMBRANE

    A. Processes to move substances across the cell membrane are essential to the life of the

       cell.

           1. Some substances cross the lipid bilayer while others cross through ion

               channels.

           2. Transport processes that mover substances across the cell membrane are either

               active or passive. (Figure 3.5)

                   a. Three types of passive processes are diffuision through the lipid

                       bilayer, diffusion through ion channels, and facilitated diffusion

                   b. Active transport requires cellular energy.

           3. Materials can also enter or leave the cell through vesicle transport.
B. Principles of Diffusion

       1. Diffusion is the random mixing of particles that occurs in a solution as a result

          of the kinetic energy of the particles. (Figure 3.6)

       2. Diffusion rate across plasma membranes is influenced by several factors:

          steepness of the concentration gradient, temperature, size or mass of the

          diffusing substance, surface area, and diffusion distance.

C. Osmosis is the net movement of a solvent through a selectively permeable membrane,

   or in living systems, the movement of water (the solute) from an area of higher

   concentration to an area of lower concentration across the membrane (Figure 3.7).

       1. Water molecules penetrate the membrane by diffusion through the lipid

          bilayer or through aquaporins, transmembrane proteins that function as water

          channels.

       2. Water moves from an area of lower solute concentration to an area of higher

          solute concentration.

       3. Osmosis occurs only when the membrane is permeable to water but not to

          certain solutes.

       4. Tonicity of a solution relates to how the solution influences the shapeof body

          cells.

              a. In an isotonic solution, red blood cells maintain their normal shape

                   (Figure 3.8a).

              b. In a hypotonic solution, red blood cells undergo hemolysis (Figure

                   3.8b).
              c. In a hypertonic solution, red blood cells undergo cremation (Figure

                  3.8c).

       5. There are important medical uses of isotonic, hypotonic, and hypertonic

           solutions.

D. Diffusion Through the Lipid Bilayer

       1. Nonpolar, hydrophobic molecules such as respiratory gases, some lipids,

           small alcohols, and ammonia can diffuse across the lipid bilayer.

       2. It is important for gas exchange, absorption of some nutrients, and excretion

           of some wastes.

E. Diffusion Through Membrane Channels

       1. Most membrane channels are ion channels, allowing passage of small,

           inorganic ions which are hydrophilic.

       2. Ion channels are selective and specific and may be gated or open all the time

           (Figure 3.9).

F. Facilitated Diffusion

       1. In facilitated diffusion, a solute binds to a specific transporter on one side of

           the membrane and is released on the other side after the transporter undergoes

           a conformational change.

       2. Solutes that move across membranes by facilitated diffusion include glucose,

           urea, fructose, galactose, and some vitamins (Figure 3.10).

G. Active Transport

       1. Active transport is an energy-requiring process that moves solutes such as

           ions, amino acids, and monosaccharides against a concentration gradient.
       2. Primary Active Transport

              a. In primary active transport, energy derived from ATP changes the

                  shape of a transporter protein, which pumps a substance across a

                  plasma membrane against its concentration gradient.

              b. The most prevalent primary active transport mechanism is the sodium

                  ion/potassium ion pump (Figure 3.11).

       3. Secondary Active Transport

              a. In secondary active transport, the energy stored in the form of a

                  sodium or hydrogen ion concentration gradient is used to drive other

                  substances against their own concentration gradients.

              b. Plasma membranes contain several antiporters and symporters

                  powered by the sodium ion gradient (Figure 3.12).

       4. Digitalis slows the sodium ion-calcium ion antiporters, allowing more calcium

          to stay inside heart muscle cells, which increases the force of their contraction

          and thus strengthens the heartbeat.

H. Transport in Vesicles

       1. A vesicle is a small membranous sac formed by budding off from an existing

          membrane.

       2. Two types of vesicular transport are endocytosis and exocytosis.

              a. Endocytosis

                      1) In endocytosis, materials move into a cell in a vesicle formed

                           from the plasma membrane.
                            2) Receptor-mediated endocytosis is the selective uptake of large

                                molecules and particles by cells (Fig 3.13).

                                    a) The steps of receptor-mediated endocytosis includes

                                         binding, vesicle formation, uncoating, fusion and

                                         endosome formation, recycling of receptors,

                                         degradation in lysosomes, and transcytosis.

                                    b) Viruses can take advantage of this mechanism to enter

                                         cells.

                            3) Phagocytosis is the ingestion of solid particles (Figure 3.14).

                            4) Pinocytosis is the ingestion of extracellular fluid (Figure 3.15).

                     b. In exocytosis, membrane-enclosed structures called secretory vesicles

                         that form inside the cell fuse with the plasma membrane and release

                         their contents into the extracellular fluid (Figures 3.13 through 3.15).

    I.   Table 3.1 summarizes the processes by which materials are transported into and out

         of cells.

V. CYTOPLASM

    A. Cytosol, the intracellular fluid, is the semifluid portion of cytoplasm that contains

         inclusions and dissolved solutes (Figure 3.1).

             1. Cytosol is composed mostly of water, plus proteins, carbohydrates, lipids, and

                 inorganic substances.

             2. The chemicals in cytosol are either in solution or in a colloidal (suspended)

                 form.

             3. Functionally, cytosol is the medium in which many metabolic reactions occur.
B. Organelles

      1. Organelles are specialized structures that have characteristic shapes and

          perform specific functions in cellular growth, maintenance, and reproduction.

      2. The Cytoskeleton

                a. The cytoskeleton is a network of several kinds of protein filaments that

                   extend throughout the cytoplasm and provides a structural framework

                   for the cell (Figure 3.16).

                b. It consists of microfilaments, intermediate filaments, and

                   microtubules.

                       1) Most microfilaments are composed of actin and function in

                           movement and mechanical support.

                       2) Intermediate filaments are composed of several different

                           proteins and function in support and to help anchor organelles

                           such as the nucleus (Figure 3.16).

                       3) Microtubules are composed of a protein called tubulin and help

                           determine cell shape and function in the intracellular transport

                           of organelles and the migration of chromosome during cell

                           division. (Figure 3.16)

      3. Centrosomes are dense areas of cytoplasm containing the centrioles, which

          are paired cylinders arranged at right angles to one another, and serve as

          centers for organizing microtubules in interphase cells and the mitotic spindle

          during cell division. (Figure 3.17)

      4. Cilia and Flagella
      a. Cilia are numerous, short, hairlike projections extending from the

         surface of a cell and functioning to move materials across the surface

         of the cell (Figure. 3.18).

      b. Flagella are similar to cilia but are much longer; usually moving an

         entire cell. The only example of a flagellum in the human body is the

         sperm cell tail (Figure 3.18).

5. Ribosomes

      a. Ribosomes are tiny spheres consisting of ribosomal RNA and several

         ribosomal proteins; they occur free (singly or in clusters) or together

         with endoplasmic reticulum (Fig 3.19).

      b. Functionally, ribosomes are the sites of protein synthesis.

6. Endoplasmic Reticulum

      a. The endoplasmic reticulum (ER) is a network of membranes that form

         flattened sacs or tubules called cisterns (Figure 3.20).

      b. Rough ER is continuous with the nuclear membrane and has its outer

         surface studded with ribosomes.

      c. Smooth ER extends from the rough ER to form a network of

         membrane tubules but does not contain ribosomes on its membrane

         surface.

      d. The ER transports substances, stores newly synthesized molecules,

         synthesizes and packages molecules, detoxifies chemicals, and

         releases calcium ions involved in muscle contraction.

7. Golgi Complex
      a. The Golgi complex consists of four to six stacked, flattened

          membranous sacs (cisterns) referred to as cis, medial, and trans (Figure

          3.21).

      b. The principal function of the Golgi complex is to process, sort, and

          deliver proteins and lipids to the plasma membrane, lysosomes, and

          secretory vesicles (Figure 3.22).

      c. Faulty routing of a specific pump protein from the nucleus through the

          Golgi complex or ER appears to be the cause of a membrane transport

          deficiency in cystic fibrosis, resulting in excessive mucus buildup in

          respiratory passages.

8. Lysosomes

      a. Lysosomes are membrane-enclosed vesicles that form in the Golgi

          complex and contain powerful digestive enzymes (Figure 3.23).

      b. Lysosomes function in intracellular digestion, digestion of worn-out

          organelles (autophagy), digestion of cellular contents (autolysis)

          during embryological development, and extracellular digestion.

      c. Tay-Sachs disease is an example of a disorder caused by faulty

          lysosomes.

9. Perioxosomes

      a. Peroxisomes are similar in structure to lysosomes, but are smaller.

      b. They contain enzymes (e.g., catalase) that use molecular oxygen to

          oxidize various organic substances.

10. Proteosomes
                  a. Proteosomes are structures that destroy unneeded, damaged, or faulty

                       proteins.

                  b. They contain proteases which cut proteins into small peptides.

                  c. Proteosomes are thought to be a factor in several diseases.

          11. Mitochondria

                  a. The mitochondrion is bound by a double membrane. The outer

                       membrane is smooth with the inner membrane arranged in folds called

                       cristae (Figure 3.24).

                  b. Mitochondria are the site of ATP production in the cell by the

                       catabolism of nutrient molecules.

                  c. Mitochondria self-replicate using their own DNA.

                  d.   Mitochondrial DNA (genes) are usually inherited only from the

                       mother.

NUCLEUS

   A. The nucleus is usually the most prominent feature of a cell (Figure 3.25).

   B. Most body cells have a single nucleus; some (red blood cells) have none, whereas

      others (skeletal muscle fibers) have several.

   C. The parts of the nucleus include the nuclear envelope which is perforated by channels

      called nuclear pores, nucleoli, and genetic material (DNA),

   D. Within the nucleus are the cell‟s hereditary units, called genes, which are arranged in

      single file along chromosomes.

          1. Each chromosome is a long molecule of DNA that is coiled together with

              several proteins (Figure 3.26).
            2. Human somatic cells have 46 chromosomes arranged in 23 pairs.

     E. The various levels of DNA packing are represented by nucleosomes, chromatin

        fibers, loops, chromatids, and chromosomes.

     F. The main parts of a cell and their functions are summarized in Table 3.2.

VII. PROTEIN SYNTHESIS

     A. Much of the cellular machinery is devoted to synthesizing large numbers of diverse

        proteins.

            1. The proteins determine the physical and chemical characteristics of cells.

            2. The instructions for protein synthesis is found in the DNA in the nucleus.

            3. Protein synthesis involves transcription and translation (Figure 3.27).

     B. Transcription

            1. Transcription is the process by which genetic information encoded in DNA is

                copied onto a strand of RNA called messenger RNA (mRNA), which directs

                protein synthesis (Figure 3.28).

                    a. Besides serving as the template for the synthesis of mRNA,DNA also

                        synthesizes two other kinds of RNA, ribosomal RNA (rRNA), and

                        transfer RNA (tRNA).

                    b. Transcription of DNA is catalyzed by RNA polymerase.

                    c. Antisense therapy blocks mRNA has been approved by the FDA

     C. Translation

            1. Translation is the process of reading the mRNA nucleotide sequence to

                determine the amino acid sequence of the protein (Figure 3.29).

            2. The sequence of translation is as follows (Figure 3.30).
                    a. Messenger RNA associated with ribosomes, which consist of tRNA

                       and proteins.

                    b. Specific amino acids attach to molecules of tRNA. Another portion of

                       the tRNA has a triplet of nitrogenous bases called an anticodon, a

                       codon is a segment of three bases of mRNA.

                    c. Transfer RNA delivers a specific amino acid to the codon; the

                       ribosome moves along an mRNA strand as amino acids are joined to

                       form a growing polypeptide.

     D. As a result of recombinant DNA techniques, genetic engineering has arisen; strains of

        recombinant bacteria produce important therapeutic substances such as human growth

        hormone, insulin, and vaccines against several viruses.

VIII. CELL DIVISION

     A. Cell division is the process by which cells reproduce themselves. It consists of

        nuclear division (mitosis and meiosis) and cytoplasmic division (cytokinesis).

            1. Cell division that results in an increase in body cells is called somaticcell

                division and involves a nuclear division called mitosis, plus cytokinesis.

            2. Cell division that results in the production of sperm and eggs is called

                reproductive cell division and consists of a nuclear division called meiosis

                plus cytokinesis.

     B. The Cell Cycle in Somatic Cells

            1. The cell cycle is an orderly sequence of events by which a cell duplicates its

                contents and divides in two. It consists of interphase and the mitotic phase

                (Figure 3.31).
2. Interphase

      a. During interphase the cell carries on every life process except

          division. Interphase consists of three phases: G1, S and G2 (Figure

          3.31).

                1) In the G1 phase, the cell is metabolically active, duplicating its

                   organelles and cytosolic components except for DNA.

                2) In the S phase, chromosomes are replicated (Figure 3.32).

                3) In the G2 phase, cell growth continues and the cell completes

                   its preparation for cell division.

      b. A cell in interphase shows a distinct nucleus and the absence of

          chromosomes (Figure 3.33a).

3. Mitotic Phase

      a. The mitotic phase consists of mitosis (or nuclear division) and

          cytokinesis (or cytoplasmic division).

      b. Nuclear division: mitosis

                1) Mitosis is the distribution of two sets of chromosomes, one set

                   into each of two separate nuclei.

                2) Stages of mitosis are prophase, metaphase, anaphase, and

                   telophase.

                       a) During prophase, the chromatin condenses and shortens

                           into chromosomes (Figure 3.33b).

                       b) During metaphase, the centromeres line up at the exact

                           center of the mitotic spindle, a region called the
                                    metaphase plate or equatorial plane region (Figure

                                    3.33c).

                                c) Anaphase is characterized by the splitting and

                                    separation of centromeres and the movement of the two

                                    sister chromatids of each pair toward opposite poles of

                                    the cell (Figure 3.33d).

                                d) Telophase begins as soon as chromatid movement

                                    stops; the identical sets of chromosomes at opposite

                                    poles of the cell uncoil and revert to their threadlike

                                    chromatin form, microtubules disappear or change

                                    form, a new nuclear envelope forms, new nucleoli

                                    appear, and the new mitotic spindle eventually breaks

                                    up.

              c. Cytoplasmic Division: Cytokinesis

                      1) Cytokinesis is the division of a parent cell‟s cytoplasm and

                          organelles. The process begins in late anaphase or early

                          telophase with the formation of a cleavage furrow (Figure 3.33

                          e).

                      2) When cytokinesis is complete, interphase begins (Figure

                          3.33f).

D. Control of Cell Destiny

       1. The three possible destinies of a cell are to remain alive and functioning

          without dividing, to grow and divide, or to die.
            2. Maturation promoting factor (MPF) induces cell division.

            3. Cell death, a process called apoptosis, is triggered either from outside the cell

                or from inside the cell due to a :cell-suicide” gene.

            4. Necrosis is a pathological cell death due to injury.

     D. Tumor-suppressor genes can produce proteins that normally inhibit cell division

        resulting in the uncontrollable cell growth known as cancer.

IX. CELLS AND AGING

     A. Aging is a normal process accompanied by a progressive alteration of the body‟s

        homeostatic adaptive responses; the specialized branch of medicine that deals with

        the medical problems and care of elderly persons is called geriatrics.

            1. The physiological signs of aging are gradual deterioration in function and

                capacity to respond to environmental stresses.

            2. These signs are related to a net decrease in the number of cells in the body and

                to the dysfunctioning of the cells that remain.

            3. The extracellular components of tissues (e.g., collagen fibers and elastin) also

                change with age.

     B. Many theories of aging have been proposed, including genetically programmed

        cessation of cell division, glucose addition to proteins, free radical reactions, and

        excessive immune responses, but non successfully answers all experimental

        objections.

     C. The effects of aging on the various body systems are discussed in their respective

        chapters.

X. CELLULAR DIVERSITY
     A. Not all cells look alike, nor do they perform identical functional roles in the body.

     B. The shapes of cells vary considerably (Figure 3.34).

XI. DISORDERS: HOMEOSTATIC IMBALANCES

     A. Cancer is a group of diseases characterized by uncontrolled cell proliferation.

            1. Cells that divide without control develop into a tumor or neoplasm.

            2. A cancerous neoplasm is called a malignant tumor or malignancy. It has the

                ability to undergo metastasis, the spread of cancerous cells to other parts of

                the body. A benign tumor is a noncancerous growth.

     B. Types of Cancer

            1. Carcinomas arise from epithelial cells.

            2. Melanomas are cancerous growths of melanocytes.

            3. Sarcomas arise from muscle cells or connective tissues.

            4. Leukemia is a cancer of blood-forming organs.

            5. Lymphoma is a cancer of lymphatic tissue.

     C. Growth and Spread of Cancer

            1. Cancer cells divide rapidly and continuously.

            2. They trigger angiogenesis, the growths of new networks of blood vessels.

            3. Cancer cells can leave their site of origin and travel to other tissues or organs,

                a process called metastasis.

     D. Causes of Cancer

            1. Environmental agents can cause cancer growth. A chemical agent. or radiation

                that produces cancer is termed a carcinogen and induces mutations in DNA.

            2. Viruses can cause cancer.
               3. Cancer-causing genes, or oncogenes, can cause cancer.

                       a. The normal counterparts of oncogenes are called proto-oncogenes;

                          these are found in every cell and carry out normal cellular functions

                          until a malignant change occurs via a mutation.

                       b. Some cancers may also be caused by genes called anti-oncogenes or

                          tumor-suppressing genes. These genes may produce proteins that

                          normally oppose the action of an oncogene or inhibit cell division.

       E. Carcinogenesis is a multistep process involving mutation of oncogenes and anti-

           oncogenes; as many as 10 distinct mutations may have to accumulate in a cell before

           it becomes cancerous.

       F. Treatment of Cancer

               1. Treatment of cancer is difficult because it is not a single disease and because

                   all the cells in a tumor do not behave in the same way.

               2. Various treatments include surgery, chemotherapy, and radiation therapy.

XII. MEDICAL TERMINOLOGY - Students should be reminded to study the medical

    terminology associated with cells.



Teaching Tips

   Display or pass around a model of a generalized cell during the lecture to help emphasize its

    three dimensional nature. Ward‟s, Carolina, or other biological supply houses carry such

    models (see Suppliers and Distributors list at the beginning of this manual).

   A small box not quite filled with a layer of ping-pong balls or marbles can be used to

    demonstrate the fluid characteristics of the plasma membrane. Cardboard rolls from toilet
    paper or paper towels can be held vertically and moved among the balls/marbles to simulate

    integral proteins. (The hole in the middle can be used to illustrate channels utilized for

    membrane transport.) Point out how the “membrane” heals itself behind the path of the

    moving protein. Also remind the students that, in reality, the balls/marbles would be two

    layers thick (representing the phospholipid bilayer).Balls of cotton or pieces of sponge can be

    placed on top of the balls to represent peripheral proteins, to help students recall that these

    can attach to either inner or outer membrane surfaces in living systems.

   The American Cancer Society is an excellent source of current information regarding trends

    in diagnosis and treatment, prevention , support for patients and families, and statistics on

    morbidity and mortality. Most local chapters are happy to provide literature and answers to

    questions.



Critical Thinking Questions

1. The systems of your body are capable of performing specialized functions that keep you alive

    and enable you to reproduce. In a very general kind of way, a cell is also capable of

    performing specific functions that maintain it on a daily basis and enable it to reproduce. For

    each of the following functions, list all of the parts of a generalized cell that might be

    involved support, movement, coordination, respiration, digestion, transportation, excretion,

    food procurement, energy production, making proteins, and reproduction.

2. How can an adult lose billions of cells from all parts of the body each day and still survive?




Educational Resources (refer to Educational Resources Appropriate for All Chapters following

the list of Suppliers and Distributors)
Videocasettes

       An Introduction to the Living Cell (30 min; 1996; FHS) - full motion computer

           animation, art, microscopic images describe cell parts and functions

       Apoptosis: Cell Death and Cancer (51 min; FHS) - studies apoptosis and its role in

           cancer

       Cancer and Metastasis (37 min, FHS)- studies biological process of cancer formation,

           live-action segment of real cancer cells

   Cell Functions: A Closer Look (25 min; 1998; FHS) - examines cell energy storage and release, protein

   synthesis, cell reproduction


Cell Motility and Microtubules (30 min, FHS) - examines cell movement and the role of

      microtubules in movement

Cells: An Introduction (25 min; 1998; FHS) - explores structure and functions of cells (both

      plant and animal) and organelle structure and function

Cells: Structure and Function (MBV) - describes how cells are specialized to perform different

      functions

Cell Wars: Understanding the Mysteries of Cancer (45 min; CBSC) - explores recent advances in

      molecular biology

Diffusion (29 min; 1990; IM) - discusses the various aspects of diffusion

Diffusion and Osmosis, 2nd ed (14 min; EBEC) - discusses the various types of diffusion and

      osmosis

DNA and RNA: Deciphering the Code of Life (39 min; 1990; VWRSP) - explores the structure

      and function of DNA and RNA; includes protein synthesis

DNA: Replication and Mitosis (14 min; FREY) - studies DNA structure, replication, Genome:

Solving the Code of Life (30 min; 1995; CBSC) - studies DNA
The Genetic Code (14 min; FREY) - details protein structure, transcription, translation, gene

      regulation, exons, introns, mutations

The Infinite Voyage: The Geometry of Life (60 min; 1990; FSE) - explores DNA to decipher its

      code

Inside the Cell: Microstructure, Mechanisms and Molecules (44 min; VWRSP) - photo-and

      electron microscopy of the cell

Introduction to Living Cells (23min; FREY) - studies cell organelles, organelle function,

      movement across membranes

The Living Body: Aging (28 min; FHS) - explores the physical process of aging

The Living Cell: An Introduction (20 min; EBEC) - examines the structure and biochemical

      process of living cells; special emphasis on protein synthesis

The Living Cell: DNA (2nd ed.) (14 min; EBEC) - uses SynthaVision to look inside a cell

       and learn how DNA codes for genetic information

The Magic of Cells (20 min; TVC) - a video tour of a cell

Map of Life: Science, Society and the Human Genome Project (46 min; 1992; CBSC) -

       disusses the human genome project and its implications

The Mitochondrion and ATP Synthesis (14 min; FREY) - details mitochondrion origin,

       structure, and function; discusses cellular respiration

Mitosis (2nd ed.) (14 min; EBEC) - excellent description of mitosis

Mitosis and Meiosis (45 min; 1990; IM) - details mitosis and meiosis

Mitosis and Meiosis: How Cells Divide (1990; GA) - details mitosis and meiosis

Molecular Miracles: Human Gene Therapy and the Future of Modern Medicine (47 min;

       1933; CBSC) - discusses gene replacement therapy
Physiological Concepts of Life (1993; WCB) - covers many topics including osmosis,

       active transport, cellular secretion, cellular respiration

Programmed Death of a Cell (30 min; FHS) - studies apoptosis

Protein Synthesis (18 min; 1990; IM) - details the events of protein synthesis

Respiration: Energy for Life (47 min; 1990; IM) - explores cellular respiration and the role of the

      mitochondrion

The Structure of the cell (21 min; CVB) - discusses basic parts and functions of the plant

       and animal cell

Translating the Code: Protein Synthesis (25 min; 1992; HRM/CBSC) - describes the

       process of protein synthesis

Visualizing Cell Processes: Cell Membrane and Transport (13 min; CBSC) - shows cell

       structure organelle function, transport across membranes

Visualizing Cell Processes: DNA Replication and Cell Reproduction (11 min; CBSC) -

       includes mitosis, chromosome condensation, cytokinesis, meiosis, DNA structure

       and bonding, enzymes, and more



Computer Resources (CD-ROMs for Windows and Macintosh platforms unless otherwise noted)

Cell Biology (SKBL) - discusses cell structure and function, mitosis and meiosis,

       membranes and cell motility

Cell Structure and Function (BIO) - electron micrographs and illustrations of cell

       components, animation showing organelle function, interactive

Continuity of Life (CEI) - explores reproductive processes, formation of tumors, stages of

       pregnancy, basic genetics
DNA: The Molecule of Life (1996; NCHCA) - explores DNA

Essentials of Human Physiology (SVE) - addresses many topics including membrane

       transport and bioelectric activity

Exploring Cell Processes (WARD) - vivid graphic with animation recreates cell

       processes

Explorations in Human Anatomy and Physiology (DGI) - covers many topics including

       active transport

From DNA to Protein (1996; SVE) - examines processes of transcription and translation;

       includes self tests

Learning More About Cells (MBV) - uses live-action video and time lapse photo-

       micrography demonstrate how cells divide, mend, gain nourishment, and

       metastasize

Life Processes and Cell Activity (SVE) - covers cell structure; cell processes such as

       transport, respiration, and photosynthesis; cell division; the chemicals of life;

       interactive

LOGAL Biology Simulations: Molecular Biology (DNA) (CEI) - covers DNA

       replication, RNA transcription and translation; interactive

Mitosis (CEI) - studies events of mitosis

The Plasma Membrane and Cellular Transport (BIO) - explains fluid-mosaic model,

       movement across membranes; interactive

Ward‟s Osmosis and Diffusion CD-ROM (WARD) - osmosis and diffusion events and

       concepts
Selected Readings

Berridge, M. J. “The Molecular Basis of Communication with the Cell,” Scientific

       American (October 1985)

Bretscher, M. S. “The Molecules of the cell Membrane,” Scientific American (October

       1985)

Cairns, J. “The Treatment of Diseases and the War Against Cancer,” Scientific American

       (November 1985)

Damell, J.E. “RNA,” Scientific American (October 1985)

Dautry-Varsat, A., and H. F. Lodish, “How Receptors Bring Proteins and Particles into

       Cells,” Scientific American (May 1984)

Duke, R. C., D. M. Ojciuis, and J. D. E. Young. “Cell Suicide in Health and Disease,”

       Scientific American (December 1996)

Glover, D. M., C. Gongalez, and J. W. Raff. “The Centrosome,” Scientific American

       (June 1993)

Grunstein, M. “Histones as Regulators of Genes,” Scientific American (October 1992)

Horwitz, A. f. “Integrins and Health,” Scientific American (May 1997)

Leinhard, G. E., J. W. Slot, D. E. James, and M. M. Muerkle. “How Cells Absorb

       Glucose,” Scientific American (January 1992)

“Making Gene Therapy Work,” Special Section, Scientific American (June 1997)

Mazia, D. “The Cell Cycle,” Scientific American (January 1974)

Murray, A. W., and M. W. Kirschner. “What Controls the Cell Cycle,” Scientific

       American (March 1991)

Porter, K. R., and J. B. Rucker. ”The Ground Substance of the Living Cell,” Scientific
       American (March 1981)

Radman, M., and R. Wagner. “The High Fidelity of DNA Duplication,” Scientific

       American (August 1988)

Rothman, J. E., “The Compartmental Organization of the Golgi Apparatus,” Scientific

       American (September 1985)

Todorov, I., N. “How Cells Maintain Stability,” Scientific American (December 1990)

Unwin, N., and R. Henderson, “The Structure of Proteins in Biological Membranes,”

       Scientific American (February 1984)

Weinberg, R. A. „Finding the Anti-Oncogene,” Scientific American (September 1988)

“What You Need to Know About Cancer,” Special Issue: Scientific American (September

       1996)

								
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