Biology And Biomedical Sciences BIOL 2960 Lecture 9: L9
13 Dec 2016
School
Department
8 February 2016
Lectures 9: Intro to Biological Membranes
I. The Plasma Membrane
A. Biological Membranes
1. The plasma membrane separated a cell from its environment, regulated what
enter/leaves a cell or cellular compartment, and is comprised of continuous
phospholipid bilayer
2. The physical organization and function of a biological membrane depends on the
constituent lipids, proteins and carbohydrates
a. Lipid bilayers comprise a major component of biological membranes
b. The phospholipid bilayer serves as a barrier to rapid passage of hydrophilic
materials (such as water, ions, polar molecules)
3. Activity: ranking the permeability of the following to a biological phospholipid
bilayer:
a. Estrogen > water > glycerol > acetic acid (pH 1.5) > sucrose > acetic acid (pH7)
b. Keep in mind that size, charge, and hydrophobicity will determine passage across
a phospholipid bilayer
4. Membrane fluidity
a. The relative amounts of saturated and unsaturated FA’s influence membrane
fluidity
b. Fully saturated (all C-C single bonds) vs.
c. Partially unsaturated FA’s (have one or more C-C double bonds, causing kinking,
bent tails, and this can affect membrane packing, increasing fluidity)
d. Animals also control membrane fluidity by incorporating cholesterol
• Cholesterols are lipids that insert into the bilayer
• The –OH on cholesterol forms H-bonds with phospholipid head groups
• This disrupts (hydrophobic) interactions between FAs to increase fluidity
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