BSC-2010 Lecture Notes - Lecture 5: Lipid Bilayer, Vegetable Oil, Cell Membrane

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20 Oct 2016
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10/3/16
CH 7
Plasma membrane is the boundary that separates the living cell from its
surroundings
Phosolipids are the most abundant lipid in the plasma membrane
Amphipathic molecule that has hydrophobic and hydrophilic regions
Phospholipids in the plasma membrane can move within the bilayer
Usually drift laterally
Rarely, a lipid may flip-flop transversely across
the membrane
As temps cool, membranes switch from fluid state to a solid state
Membranes rich in unsaturated fatty acids are more fluid than those rich in
saturated fatty acids
Membranes must be fluid to work properly; they are usually about as fluid as
salad oil
At warm temp, 37 C, cholesterol restrains movement of phospholipids
A membrane is a collage of different proteins, often grouped together,
embedded in the fluid matrix of the lipid bilayer
Integral proteins penetrate the hydrophobic core
Six major functions of membrane proteins
o Transport
o Enzymatic activity
o Signal transduction
o Cell-cell recognition
o Intercellular joining
o Attachment to the cytoskeleton and extracellular matrix (ECM)
Transport proteins allow passage of hydrophilic substances across the
membrane
Some transport proteins, called channel proteins, have a hydrophilic channel
that certain molecules or ions can use as a tunnel
Channel proteins called aquaporin’s facilitate the passage of water
Diffusion is the tendency for molecules to spread out evenly into the
available space
Osmosis is the diffusion of water across a selectively permeable membrane
Tonicity is the ability of a surrounding solution to cause a cell to gain or lose
water
Isotonic solution: Solute concentration is the same as that inside the cell; no
net water movement across the plasma membrane
Hypertonic solution: Solute concentration is greater than that inside the cell;
cell loses water
Hypotonic solution: Solute concentration is less than that inside the cell; cell
gains water
Osmoregulation, the control of solute concentrations and water balance, is a
necessary adaptation for life in such environments
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