Membrane Bilayer Flashcards
General function of biological membranes
Continuous, highly selected permeability barrier
control of the enclosed chemical environment
communication
recognition - signalling molecules
single generation in response to stimuli
Our all membranes the same
Different regions of plasma membrane may have different functions. E.g. secretion transport synapse in nerve junctions
Membrane composition
40% lipid
60% protein
1 to 10% carbohydrate
Membranes are hydrated structures thus 20% of total weight is water
Which lipids are involved in biological membranes
Phospholipids
glycolipids
cholesterol
Membrane lipids contain both hydrophilic and hydrophobic head this is called
amphipathic
Phospholipid structure
Two fatty acid tales. 16 to 18 carbons long is the most common, cis double bonds to introduce kinks
Glycerol which is a free carbon structure
Phosphate
Head group such as choline, sugar, amino acids
sphingomyelin structure
This is a phospholipid but not on a glycerol backbone
backbone is sphingosine
as one fatty acid tail and one tile of phosphate attached to choline
Glycolipids
Two fatty acid tales, glycerol, sugar
Phospholipid motion
- Flexion
- Rotation
- Lateral diffusion
- Flip-flop
What does cis double bonds due to the membrane structure
Help stabilise the structure
How does collateral contribute to marine stability
Has polar head group, planar a ring structure and nonpolar hydrocarbon tale.
Cholesterol stabilisers membrane so that it is fluid at low temperature and at high temperature stabilises member about too much motion
Explain the paradoxical effect of Cholesterol in phospholipid bilayerlayers
cholesterol polar group housed bonds to fatty acid tale - reduces the phospholipid chain motion reduces fluidity
However also stops phospholipid fatty acid tales becoming too closely packed together hence increases fluidity
