Molecules of Life - DOC by fjwuxn


									                        Molecules of Life
                              Chapter 3
Impacts, Issues:
Fear of Frying
 Trans fats in hydrogenated vegetable oil raise levels of cholesterol
  in our blood more than any other fat, and directly alter blood vessel

Organic Molecules

 All molecules of life are built with carbon atoms

 We can use different models to highlight different aspects of the
  same molecule
3.1 Carbon – The Stuff of Life

 Organic molecules are complex molecules of life, built on a
  framework of carbon atoms
   •   Carbohydrates
   •   Lipids
   •   Proteins
   •   Nucleic acids
Carbon – The Stuff of Life

 Carbon atoms can be assembled and remodeled into many organic
   • Can bond with one, two, three, or four atoms
   • Can form polar or nonpolar bonds
   • Can form chains or rings

Representing Structures
of Organic Molecules
 Structural model of an organic molecule
  • Each line is a covalent bond; two lines are double bonds; three lines
    are triple bonds

Representing Structures
of Organic Molecules
 Carbon ring structures are represented as polygons; carbon atoms
  are implied

Representing Structures
of Organic Molecules
 Ball-and-stick models show positions of atoms in three dimensions;
  elements are coded by color

Representing Structures
of Organic Molecules
 Space-filling models show how atoms sharing electrons overlap

3.2 From Structure to Function

 The function of organic molecules in biological systems begins with
  their structure

 The building blocks of carbohydrates, lipids, proteins, and nucleic
  acids bond together in different arrangements to form different
  kinds of complex molecules
Functional Groups

 Hydrocarbon
  • An organic molecule that consists only of hydrogen and carbon atoms

 Most biological molecules have at least one functional group
  • A cluster of atoms that imparts specific chemical properties to a
    molecule (polarity, acidity)
What Cells Do to Organic Compounds

 Metabolism
  • Activities by which cells acquire and use energy to construct,
    rearrange, and split organic molecules
  • Allows cells to live, grow, and reproduce
  • Requires enzymes (proteins that increase the speed of reactions)

What Cells Do to Organic Compounds
 Condensation
  • Covalent bonding of two molecules to form a larger molecule
  • Water forms as a product

 Hydrolysis
  • The reverse of condensation
  • Cleavage reactions split larger molecules into smaller ones
  • Water is split
What Cells Do to Organic Compounds

 Monomers
  • Molecules used as subunits to build larger molecules (polymers)

 Polymers
  • Larger molecules that are chains of monomers
  • May be split and used for energy
3.1-3.2 Key Concepts:
Structure Dictates Function

 We define cells partly by their capacity to build complex
  carbohydrates and lipids, proteins, and nucleic acids

 All of these organic compounds have functional groups attached to
  a backbone of carbon atoms
3.3 Carbohydrates

 Carbohydrates are the most plentiful biological molecules in the

 Cells use some carbohydrates as structural materials; others for
  stored or instant energy


 Carbohydrates
  • Organic molecules that consist of carbon, hydrogen, and oxygen in a
    1:2:1 ratio

 Three types of carbohydrates in living systems
  • Monosaccharides
  • Oligosaccharides
  • Polysaccharides
Simple Sugars
 Monosaccharides (one sugar unit) are the simplest carbohydrates
  • Used as an energy source or structural material
  • Backbones of 5 or 6 carbons
  • Example: glucose

Short-Chain Carbohydrates
 Oligosaccharides
  • Short chains of monosaccharides
  • Example: sucrose, a disaccharide

Complex Carbohydrates
 Polysaccharides
  • Straight or branched chains of many sugar monomers

 The most common polysaccharides are cellulose, starch, and
  • All consist of glucose monomers
  • Each has a different pattern of covalent bonding, and different
    chemical properties
 Chitin
  • A nitrogen-containing polysaccharide that strengthens hard parts of
    animals such as crabs, and cell walls of fungi

3.3 Key Concepts:

 Carbohydrates are the most abundant biological molecules

 They function as energy reservoirs and structural materials

 Different types of complex carbohydrates are built from the same
  subunits of simple sugars, bonded in different patterns
3.4 Greasy, Oily – Must Be Lipids

 Lipids function as the body’s major energy reservoir, and as the
  structural foundation of cell membranes

 Lipids
  • Fatty, oily, or waxy organic compounds that are insoluble in water
Fatty Acids

 Many lipids incorporate fatty acids
  • Simple organic compounds with a carboxyl group joined to a
    backbone of 4 to 36 carbon atoms

 Essential fatty acids are not made by the body and must come
  from food
  • Omega-3 and omega-6 fatty acids
Fatty Acids
 Saturated, monounsaturated, polyunsaturated

 Fats
  • Lipids with one, two, or three fatty acids “tails” attached to glycerol

 Triglycerides
  • Neutral fats with three fatty acids attached to glycerol
  • The most abundant energy source in vertebrates
  • Concentrated in adipose tissues (for insulation and cushioning)
Saturated and Unsaturated Fats

 Saturated fats (animal fats)
  • Fatty acids with only single covalent bonds
  • Pack tightly; solid at room temperature

 Unsaturated fats (vegetable oils)
  • Fatty acids with one or more double bonds
  • Kinked; liquid at room temperature

Trans Fats

 Trans fats
  • Partially hydrogenated vegetable oils formed by a chemical
    hydrogenation process
  • Double bond straightens the molecule
  • Pack tightly; solid at room temperature

 Phospholipids
  • Molecules with a polar head containing a phosphate and two nonpolar
    fatty acid tails
  • Heads are hydrophilic, tails are hydrophobic
  • The most abundant lipid in cell membranes
 Waxes
   • Complex mixtures with long fatty-acid tails bonded to long-chain
     alcohols or carbon rings
   • Protective, water-repellant covering

Cholesterol and Other Steroids

 Steroids
   • Lipids with a rigid backbone of four carbon rings and no fatty-acid tails

 Cholesterol
   • Component of eukaryotic cell membranes
   • Remodeled into bile salts, vitamin D, and steroid hormones
     (estrogens and testosterone)
3.4 Key Concepts:

 Lipids function as energy reservoirs and waterproofing or
  lubricating substances

 Some are remodeled into other substances

 Lipids are the main structural components of cell membranes
3.5 Proteins – Diversity
in Structure and Function

 Proteins are the most diverse biological molecule (structural,
  nutritious, enzyme, transport, communication, and defense

 Cells build thousands of different proteins by stringing together
  amino acids in different orders
Proteins and Amino Acids
 Protein
   • An organic compound composed of one or more chains of amino

 Amino acid
   • A small organic compound with an amine group (—NH3+), a carboxyl
     group (—COO-, the acid), and one or more variable groups (R group)

 Protein synthesis involves the formation of amino acid chains
  called polypeptides

 Polypeptide
   • A chain of amino acids bonded together by peptide bonds in a
     condensation reaction between the amine group of one amino acid
     and the carboxyl group of another amino acid
Levels of Protein Structure

 Primary structure
   • The unique amino acid sequence of a protein

 Secondary structure
   • The polypeptide chain folds and forms hydrogen bonds between
     amino acids

Levels of Protein Structure

 Tertiary structure
   • A secondary structure is compacted into structurally stable units
     called domains
   • Forms a functional protein

 Quaternary structure
   • Some proteins consist of two or more folded polypeptide chains in
     close association
   • Example: hemoglobin
3.6 Why Is Protein Structure
 So Important?
 When a protein’s structure goes awry, so does its function

Just One Wrong Amino Acid…

 Hemoglobin contains four globin chains, each with an iron-
  containing heme group that binds oxygen and carries it to body

 In sickle cell anemia, a DNA mutation changes a single amino acid
  in a beta chain, which changes the shape of the hemoglobin
  molecule, causing it to clump and deform red blood cells
Proteins Undone – Denaturation

 Proteins function only as long as they maintain their correct three-
  dimensional shape

 Heat, changes in pH, salts, and detergents can disrupt the
  hydrogen bonds that maintain a protein’s shape

 When a protein loses its shape and no longer functions, it is
3.5-3.6 Key Concepts:

 Structurally and functionally, proteins are the most diverse
  molecules of life

 They include enzymes, structural materials, and transporters

 A protein’s function arises directly from its structure
3.7 Nucleic Acids

 Some nucleotides are subunits of nucleic acids such as DNA and
 Some nucleotides have roles in metabolism

 Nucleotide
  • A small organic molecule consisting of a sugar with a five-carbon ring,
    a nitrogen-containing base, and one or more phosphate groups

  • A nucleotide with three phosphate groups
  • Important in phosphate-group (energy) transfer

Nucleic Acids

 Nucleic acids
  • Polymers of nucleotides in which the sugar of one nucleotide is
    attached to the phosphate group of the next
  • RNA and DNA are nucleic acids


 RNA (ribonucleic acid)
  • Contains four kinds of nucleotide monomers, including ATP
  • Important in protein synthesis


 DNA (deoxyribonucleic acid)
  • Two chains of nucleotides twisted together into a double helix and
    held by hydrogen bonds
  • Contains all inherited information necessary to build an organism,
    coded in the order of nucleotide bases
3.7 Key Concepts:
Nucleotides and Nucleic Acids

 Nucleotides have major metabolic roles and are building blocks of
  nucleic acids

 Two kinds of nucleic acids, DNA and RNA, interact as the cell’s
  system of storing, retrieving, and translating information about
  building proteins

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