Cells

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Cells

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

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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)

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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

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Cells/ Cell Membranes/phospholipids
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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

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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

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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.

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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)

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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)

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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)

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Cells/ Cell Membranes

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

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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

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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
• - -

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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.

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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

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Cells/ Cell Membranes/Endocytosis
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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

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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.

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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.

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Cells/ Cell Membranes/ Movement of materials
across membranes
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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

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Cells/ Cell Membranes/ Movement of materials
across membranes