BIOL130 Chapter Notes - Chapter 6: Phosphatidylethanolamine, Phosphatidylinositol, Phosphatidylcholine

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5 Aug 2016
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Unit 6 Biological Membranes
Membrane functions:
- selectively permeable barrier
- transports solutes/molecules across membrane
- respond to external signals
- energy transduction/harvesting
- compartmentalization (in eukaryotes): create separate environments for different activities
- scaffold for biochemical activities
all membrane lipids are amphipathic: posses both hydrophobic and hydrophilic regions
phospholipid tails
- tightly packed tails  membrane more viscous, less fluid
- freely moving tails  higher fluidity
length: from 14-24 carbons, 18-20 carbons most common (shorter = more fluid)
saturated fatty acids  no double bonds (tightly packed: not so fluid  butter)
unsaturated fatty acids  have double bonds (cant tightly pack: fluid  oil)
cholesterol makes membrane stiffer – less fluid
at very low temperature, hydrophobic tails pack together and membrane ‘gels’ (solidifies)
to maintain membrane fluidity for normal cell function
- change composition of membranes
- alter phospholipids
- desaturate fatty acids (makes it more fluid to deal with the cold)
- change length of FA chains (yeast, bacteria)
- adjust amount of cholesterol (animals)
Asymmetry of lipid bilayer
appearance of PS in outer ‘leaflet’ of membrane usually indicates that cell is going to die
Human RBCs as ‘Model Organisms’ for Plasma Membrane
simple – no nucleus, no ER, no mitochondria, no lysosomes = very pure preps of plasma
membranes
intact plasma membranes prepared by RBC ghosts
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