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The Cellular Level of Organization Chapter 3 – Cells The

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									Chapter 3 – Cells: The Living Units

The _____is the basic unit of structure and function in the body.
Cells were first observed by English scientist __________________.

This chapter is concerned with cell structure (cytology) and cell function (cell physiology).

Cell Theory
     Proposed by Matthias Schleiden and Theodor Schwann,
     Extended by German pathologist ____________.
     Has four concepts:
       1)    A cell ________________________________
       2)    The activity ____________________________
       3)    Biochemical activities _______________________
       4)    _________________ has a cellular basis.



A Generalized View of the Cell

A cell can be divided into three parts:
        1) __________ membrane
             separates internal environment from external environment
             acts as a ______________ into and out of the cell
             involved in communication with other cells
        2) ________
             all cellular contents between cell membrane and nuclear membrane
             ______ - fluid portion of cytoplasm
             contains organelles, each with a specific function
        3) _______
             contains chromosomes (DNA)



THE PLASMA MEMBRANE: STRUCTURE
Best described by the ________________
         lipids that make up membrane move around --> fluid
         contains many different types of proteins --> mosaic
Framework of membrane is a lipid bilayer, made up of cholesterol (20%), phospholipids (75%),
    and glycolipids (5%).
Arrangement due to amphipathic nature of these molecules (have both polar and nonpolar
parts).
Membrane proteins are divided into two categories:
         _______ proteins - extend through lipid bilayer
         _______ proteins - associated with proteins or lipids on outer surface of membrane
            (internally or externally)
Many membrane proteins are glycoproteins, containing attached ______ groups --> help to make
up _________ or outer surface of cell.


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      serves as a molecular “signature” for each cell for recognition
      allows cells to adhere to one another in tissues
      makes outside of cell “slippery” due to attraction of water molecules --> easier to move

Functions of cell membrane proteins:
       1) ________ - have a pore or hole through which ions can travel
       2) _______________ - bind to ion or molecule to move it across membrane
       3) _______ - bind a specific molecule, such as a hormone
       4) ____________
       5) _____________ - identifies self vs. non-self
       6) _______ - connect cells to each other or link inside and outside of a cell
Maintaining membrane fluidity is crucial to cell function.
    prevents cells from rupturing if torn or punctured
    cells that accumulate an excess of cholesterol are less fluid and stiffer -->
       atherosclerosis or “hardening of the arteries” of blood vessels



SPECIALIZATIONS OF THE PLASMA MEMBRANE

Microvilli
    defined as __________ projections of the plasma membrane
    serve to _______________________



Membrane Junctions
There are three factors that act to bind cells together:
    glycoproteins in the glycocalyx
    wavy contours of membranes of adjacent cells
    special membrane junctions
There are three cell junctions::
       1) ____________
            found in cells of tissues that line organ surfaces or body cavities
            prevent passage of materials between cells --> prevents leaking of blood or body
               fluids
            common in _________________________
       2) __________ or anchoring junctions
            made of plaque and linked to adjacent cells across space between cells
            help attach cells to each other
            common in __________________________
       3) __________ or a nexus
            proteins called connexons extend between cytoplasms of two cells --> tunnel
            allows ions and molecules to be exchanged in the cytoplasm
            common in cells in embryonic tissues, smooth muscle, cardiac muscle, and nerve
              cells




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THE PLASMA MEMBRANE: FUNCTIONS

Membrane Transport
Cells must be able to transport ions and molecules into the cell to support metabolic reactions
    (i.e. glucose for glycolysis) and export waste products --> lots of exchange across the
    membrane.
Molecules can be transported across biological membranes based upon two criteria:
    1) mediated - use of a transporter protein
    2) nonmediated - no transporter protein needed
Molecules can also be transported either actively or passively:
    1) active - cellular energy, usually ATP is necessary to move molecule “uphill” against its
         concentration gradient
    2) passive- molecule moves “downhill” with it concentration gradient

Passive Processes
There are two passive transport processes used to move molecules:
   1) diffusion
   2) filtration

Diffusion

Defined as the movement of molecules via their kinetic energy downhill or down their
    concentration gradient until equilibrium is reached.
Equilibrium is reached when the molecules are evenly distributed throughout the solution.
Example: crystal of dye in water
Several factors influence rate of diffusion:
    1)
    2)
    3)
    4)
    5)
There are three types of diffusion:
    1) simple diffusion
    2) facilitated diffusion
    3) osmosis

Facilitated Diffusion
Movement of molecules that are too polar or highly charged to cross on their own.
Mediated by transporter protein or carrier protein.
Solute molecule binds to transporter, which changes shape and then is able to release solute on
other side of membrane.
Example: glucose transport via GluT protein on cell membrane


Osmosis
Defined as the net movement of solvent (usually water) through a selectively permeable
   membrane from an area of higher concentration to an area of lower concentration.


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Only occurs when a membrane is permeable to water but not other solutes (i.e. glucose).
In the cells of the body, tonicity (number of dissolved solutes) also affects osmosis.
     Isotonic - concentration of solutes is equal across membrane; no net movement of water
     Hypotonic - fewer dissolved solutes; water will enter cell and cause cells to burst;
        distilled water is an extremely hypotonic solution; water
     Hypertonic - greater number of dissolved solutes; water will leave cell and cause it to
        shrink
Water can also travel through aquaporins, channel proteins that are abundant in kidney cells and
    red blood cells.

Thought question: Why are most intravenous solutions isotonic, rather than hypotonic or
   hypertonic?



Filtration
Process that moves water and solutes through a membrane by fluid or hydrostatic pressure.
Passive process, although pressure gradient is used.

Active Transport
Defined as movement of solute “uphill” or against its concentration gradient via use of energy.
There are two types of active transport:
       1) primary active transport
               use energy from breaking bond in ATP to pump solute across membrane
               Example: Na+/K+ ATPase pump or sodium pump
       2) secondary active transport
              use concentration gradient for one solute to drag another solute
              uses same carrier protein
              example: Na+-glucose symport transporter

Vesicular Transport
Vesicle is a small, membranous sac formed from a preexisting membrane.
There are two main types of vesicular transport:
        1) endocytosis - material is brought into cell from cell membrane
                a) receptor-mediated endocytosis
                      used by cells to take up transferrin, vitamin B12, low density lipoproteins
                        (LDLs)
                      receptors are usually recycled to cell surface; contents degraded by
                        lysosome
                b) pinocytosis or bulk-phase endocytosis
                      nonselective uptake of droplets of extracellular fluid
                c) phagocytosis
                      large, solid particles are taken in by the cell
                      done by macrophages of immune system and WBCs to protect body
                        against foreign invaders (bacteria or viruses)
        2) exocytosis - materials are exported from the cell



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                      may be a waste product or a useful product (hormone, neurotransmitter,
                       digestive enzyme)

Generating and Maintaining a Resting Membrane Potential

A cell membrane is said to be _________ __________ - allows some substances to pass more
    readily than others.
Lipid bilayers are permeable to _______, uncharged molecules such as oxygen, carbon dioxide,
    steroid hormones.
Lipid bilayer is impermeable to glucose, charged ions (Na +, K+, etc.) --> but these are
   transported across lipid bilayers --> transporters do the job.
The cell maintains different concentrations of ions and molecules on either side of the
   membrane --> establishes a _________________ (difference in concentration across
   membrane).
                         +
              O2 and Na more concentrated outside cell
                         +
              CO2 and K are more concentrated inside cell
Because many of the molecules that are maintained in different concentrations are also
charged, must talk about the ___________________of an ion.
            takes into account both the concentration gradient and electrical gradient
            inside of cell is slightly negatively charged (has a membrane potential)

THE CYTOPLASM
    Cytoplasm can be divided into two compartments:
            1) cytosol
            2) organelles

Cytosol
    Fluid portion of the cell.
    Contains 75-90% water plus dissolved solutes such as ions, glucose, amino acids, fatty
        acids, proteins, ATP, waste products, etc.
    Site of many chemical reactions in the cell.

Organelles
    Defined as specialized structures that perform specific functions involved in
       maintaining the cell.
    Each organelle contains its own set of enzymes and carries out its own specific
       physiological processes.

Mitochondria
     function in generation of ATP --> powerhouses of the cell
     part of aerobic phase of cellular respiration --> most abundant in cells with high ATP
       demands, such as ____________
     are maternally inherited
Ribosomes
     sites of protein synthesis


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     contain ribosomal RNA (rRNA) and protein
     composed of two subunits, a large and small subunit
Endoplasmic reticulum
     network of flattened sacs or tubules; very extensive
     there are two types in cells:
        1) rough ER - synthesize proteins for secretion, synthesizes membrane phospholipids;
        have ribosomes associated with them
        2) smooth ER - synthesizes phospholipids, fats, steroids
Golgi complex or Golgi apparatus
     all proteins made by ER are transported to Golgi via vesicles
     consists of membranous sacs with bulging edges
     typical cell contains only one Golgi
     vesicles are used to transport cargo from one cistern to the next
     responsible for modifying proteins produced by ER, adding sugars to proteins -->
        glycoproteins, adding sugars to lipids --> glycolipids
Lysosomes
     contain powerful digestive enzymes called acid hydrolases
     can break down all molecules delivered to it
     also responsible for autophagy (self-eating) of worn out or old organelles and autolysis
        (responsible for tissue deterioration following death)
     also used by sperm, which release lysosomal contents extracellularly to dissolve surface
        of ovum
Peroxisomes
     contain peroxidases, which remove hydrogen atoms from organic molecules
     oxidize toxic substances, such as alcohol
     produce a by-product called hydrogen peroxide, which is toxic
     enzyme catalase decomposes hydrogen peroxide to oxygen and water

Cytoskeleton
          several different kinds of protein filaments throughout the cytosol
          provides a structural framework for the cell
          organizes the organelles
          composed of three types of protein filaments:
             1) microfilaments
                  made of actin and located near the periphery of the cell
                  involved in muscle contraction, cell division, cell movement
                  anchor cytoskeleton to cell membrane
                  support microvilli (microscopic projections of cell membrane; found in
                     intestinal epithelial cells, for example)
             2) intermediate filaments
                  found in cells that experience a lot of mechanical stress (epithelial cells
                     of the skin)
                  help anchor nucleus
             3) microtubules
                  made of tubulin and grow from centrosome
                  help determine cell shape


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                      function in intracellular transport of organelles, such as vesicles
                      make up cilia and flagella
   2) centrosome
           region near nucleus from which microtubules “grow”
           contain a pair of centrioles - play role in formation of cilia and flagella
             is a microtubule organizing center (MTOC) for the mitotic spindle
   3) cilia and flagella
           cilia are short, numerous, hair-like projections that extend from the cell surface
           contain a 9+2 arrangement of microtubules that is anchored by the basal body
           when beating, propels fluid pass the surface of the cell
           found in two locations:
           flagella are longer and fewer in number
           also contain 9+2 arrangement of microtubules
           only example is the flagellum on a _____ cell
               4)
               5)
               8)



THE NUCLEUS

Most cells contain only one nucleus, but mature RBCs have none (anucleate) and skeletal muscle
cells contain many (multinucleate).
Separated from cytoplasm by nuclear membrane or nuclear envelope, which contains nuclear
pores.
Contain one or more nucleoli (groups of proteins, DNA, and RNA) --> sites of ribosome synthesis.
Contains chromosomes (2 sets of 23 chromosomes, one from Mom and one from Dad) that
    appear as chromatin in nondividing cells.

Protein Synthesis
Proteins are one of the most important biological macromolecules in the cell.
Many are enzymes that catalyze chemical reactions; others are hormones, antibodies,
    components of the cytoskeleton, etc.
The instructions for making these proteins come from the DNA in the nucleus (known as the
    Central Dogma of Molecular Biology).
The information in the DNA (in the form of nucleotides) is transcribed into another type of
    nucleic acid (RNA), which is then translated in the cytoplasm into a sequence of amino acids
    to make the protein.
The sequence of three nucleotides is known as a base triplet.
Each triplet is transcribed into a complementary sequence of RNA called a codon.
Each codon specifies an amino acid.

Transcription
DNA serves as a template for copying the information into a complementary sequence of
   nucleotides in the form of RNA, specifically messenger RNA or mRNA.
The enzyme that does this is called RNA polymerase.


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Starts at a sequence of DNA called a promoter and continues until it reaches the terminator.
As the enzyme moves along the DNA, it “reads” the DNA strand and assembles a complementary
       RNA strand.
               adenine --> thymine (DNA) or uracil (RNA)
               cytosine --> guanine

Translation
The nucleotide sequence of mRNA is translated into a sequence of amino acids that make up a
protein.
The protein/RNA complex responsible for “reading” the mRNA is a ribosome.
It “reads” each codon and bonds together the corresponding amino acid.
Occurs in the cytoplasm.



Normal Cell Division
Cell division is a process in which damaged, old, or geriatric cells replace themselves.
There are two types of cell division:
    1) somatic cell division
         - mitosis (division of nucleus) and cytokinesis (division of cytoplasm)
         - production of two genetically identical daughter cells
    2) reproductive cell division
         - meiosis
         - used to produce gametes that have half the number of chromosomes of the original
    cell



The Cell Cycle in Somatic Cells
Cell cycle is a series of events during which the cell duplicates and divides its genetic material.
All somatic or body cells contain 23 pairs of chromosomes called homologous chromosomes.
These chromosomes must be replicated then distributed to the two cells to be produced.
There are several phases to the cell cycle:
    1) Interphase
        - state of high metabolic activity
        - divided into three phases:
                 1) G1 - duplication of organelles and cytoplasmic components
                2) S - DNA duplication or replication
                3) G2 - preparation for cell division
        - G0 state -
    2) Mitosis (M phase)
        - nuclear division and cytokinesis
        - divided into four phases:
                1) prophase
                          - chromatin condenses and shortens --> becomes visible
                         - nucleolus disappears
                         - nuclear envelope breaks apart


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                2) metaphase
                        - chromosomes line up along cell equator
                3) anaphase
                        - homologous chromosomes pulled to opposite sides of cell
                4) telophase
                        - reverse of prophase
                5) cytokinesis - pinching of cell via a cleavage furrow

Control of Cell Destiny
A cell has three destinies:
        1) stays alive, but does not divide
        2) remain alive, but grow and divide
        3) die

All of these decisions are carefully regulated in the cell, particularly cell death or apoptosis.
     used to remove unneeded cells following birth
     used to regulate the number of cells in a tissue
     may be used to eliminate potentially dangerous cells (cancer)



Homeostatic Imbalances

wound “weeping”



familial hypercholesterolemia



Tay-Sachs disease




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