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Cells

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A. Cell Membrane Structure. 1. Phospholipid bilayer. 2. Transmembrane proteins ... Cell Membranes ... and move around in membrane (ex. Mouse/human cell expt. ... – PowerPoint PPT presentation

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Title: Cells


1
Cells
  • A. Cell Membrane Structure
  • 1. Phospholipid bilayer
  • 2. Transmembrane proteins
  • 3. Support fibers

2
Cells/ Cell Membranes
  • 1. Phospholipid bilayer
  • glycerol with two fatty acid chains alcohol
    bonded with phosphate
  • F.A. chains are hydrophobic/ alcohol and
    phosphate end hydrophilic
  • Phospholipids are amphipathic (hydrophilic and
    hydrophobic ends on the same molecule)

3
Cells/ Cell Membranes/phospholipids
  • Since water is present inside and outside of
    cells, phospholipids must exist in a bilayer
    arrangement.
  • Hydrophilic ends toward the surfaces/ hydrophobic
    ends toward the middle

4
Cells/ Cell Membranes/phospholipids
5
Cells/ Cell Membranes
  • 2. Transmembrane proteins
  • Held in membrane with hydrophilic/hydrophobic
    interactions
  • Many can float and move around in membrane (ex.
    Mouse/human cell expt.)
  • Serve a variety of functions in the membrane
  • a. transport c. receptors e. adhesion
  • b. enzymes d. cytoskeleton f. identity

6
Cells/ Cell Membranes/Transmembrane proteins
  • a. Transport
  • proteins that transect the membrane and serve as
    channels to allow specific molecules to
    enter/leave the cell
  • b. Enzymes
  • proteins that are bound to membrane and project
    inward in order to catalyze cell reactions

7
Cells/ Cell Membranes/Transmembrane proteins
  • c. Receptor proteins
  • proteins transecting membrane that have receptor
    sites on outside of membrane. When a hormone
    binds with the receptor site, the protein causes
    the cell to change its activities.

8
Cells/ Cell Membranes/Transmembrane proteins
  • d. Cytoskeleton
  • certain membrane proteins exist to bind to the
    cytoskeleton as an attachment point so the cell
    can take on a particular shape.
  • e. Adhesion
  • some proteins exist to adhere to a neighboring
    cells adhesion proteins to form a temporary or
    permanent bond with the neighboring cell.
    (desmosome)

9
Cells/ Cell Membranes/Transmembrane proteins
  • f. Cell identity
  • glycoproteins (carboh. protein) exist in the
    cell membrane to identify the cell as self.
    (used in cell recognition for immune system)
  • glycolipids (carboh. lipid) exist in the
    membrane to identify tissue type (ABO blood group)

10
Cells/ Cell Membranes
  • 3. Support fibers
  • some fibers pull on cytoskeleton proteins in the
    membrane to hold a cell in a particular shape
    (e.g. red blood cells.)
  • some fibers anchor proteins so they dont float
    around too much in the membrane (e.g. channel
    proteins on the surface of a membrane)

11
Cells/ Cell Membranes
  • B. Movement of materials across membranes
  • 1. Diffusion
  • 2. Osmosis
  • 3. Facilitated diffusion
  • 4. Endocytosis/Exocytosis
  • 5. Active transport

12
Cells/ Cell Membranes/ Movement of materials
across membranes
  • 1. Diffusion definition-
  • mvmnt of matl from areas of greater conc. to
    areas of lesser conc.
  • Factors affecting diffusion rate
  • temperature
  • Concentration gradient
  • Size of molecules
  • Phase of material in which diff. is occurring

13
Cells/ Cell Membranes/ Movement of materials
across membranes
  • 2. Osmosis definition
  • movement of water/solvent across membranes from
    an area of high conc. to an area of lower conc.
  • Factors affecting osmosis rate
  • -Temp. -conc. Gradient
  • -size of molecules - size of membrane pores
  • - -

14
Cells/ Cell Membranes/ Movement of materials
across membranes
  • 3. Facilitated diffusion definition
  • movement of substances across cell membranes
    using a carrier molecule from an area of high
    conc. to an area of lower conc.

15
Cells/ Cell Membranes
  • Endocytosis/ Exocytosis
  • Endocytosis is taking in of large amounts of
    materials or large particles/cells by surrounding
    with a part of the cell membrane

16
Cells/ Cell Membranes/Endocytosis
17
Cells/ Cell Membranes/ Movement of materials
across membranes
  • 5. Active transport
  • mvmnt of materials across cell memb. against a
    concentration gradient (low -gt high) requiring
    use of the cells energy reserves.
  • Ex. Proton pump
  • Sodium/potassium pump

18
Cells/ Cell Membranes/ Movement of materials
across membranes
  • Proton pump
  • Carrier protein on membrane of cell has active
    site for H.
  • When H binds to protein, an ATP is used to
    change the shape of the protein moving H to the
    outside of the cell.
  • This is a very old mechanism seen in
    prokaryotes and eukaryotes.

19
Cells/ Cell Membranes/ Movement of materials
across membranes
  • Sodium-Potassium pump
  • Carrier protein in cell membrane has binding
    sites for Na and K but NOT AT THE SAME TIME.
  • 3 Na bind to the Na active site, and ATP is
    used to move them to the outside of the cell and
    P is attached to carrier protein. Once Na is
    released, protein changes its shape to open K
    binding sites. Two K bind to sites and protein
    changes shape back to move K to cytoplasm.
    Phosphate is released from protein.

20
Cells/ Cell Membranes/ Movement of materials
across membranes
21
Cells/ Cell Membranes/ Movement of materials
across membranes
  • Why move protons and/or Na against conc.
    gradient?
  • This is stored energy!
  • Coupled channels
  • cotransport
  • countertransport

22
Cells/ Cell Membranes/ Movement of materials
across membranes
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