S1 Flashcards
What are the functions of biological membranes?
- highly selective permeabilty barrier
- Control of the enclosed chemical environment
- communication
- recognition-signalling molecules
i. Adhesion proteins
ii. Immune surveillance - signal generation in response to stimuli (electrical, chemical)
Dry weight general membrane composition
40% lipid
60% protein
1-10% carbohydrate
Membranes are hydrated structures. What is the total weight of water in membranes?
20%
What are the four different types of phospholipid head groups?
Choline, Serine, Ethanolamine and Inositol
Name a phospholid with a special head group
Sphingomyelin
Name two types of glycolipids
Cerebroside
Ganglioside
What is the difference between cerebrosides and ganglioside?
C: Lipids with head group sugar monomer whereas G: Lipids with head group oligosaccharide (sugar multimers).
Draw a lipid micelle
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Lipid micelle
What is liposome?
Lipid bilayer around a cell
Draw a lipid bilayer
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What motions are possible with phospholipids?
Flexion, rotation, flip flop (rare) and lateral diffusion
What influence does a cis double bond have in bilayer structure?
Reduces phospholipid packing so increases fluidity.
Describe the structure of cholesterol
Polar head group on top of a rigid planar steriod structure with a non-polar hydrocarbon tail.
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What’s the effect of cholesterol concentration on the endothermic phase transition of phospholipid bilayers?
As cholesterol concentration increases endothermic phase transition decreases.
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Where does cholesterol insert and bind in the phospholipid bilayer?
Cholesterol inserts between the hydrophobic tails of phospholipids and the polar OH group of the cholesterol binds to the double bonded O of the ester group in the phospholipid.
How does cholesterol restrict motion of phospholipid tails?
The upper region of the phospholid tail is aligned with the rigid steriod structure of cholesterol so it’s motion is restricted. However, the lower region of the phospholid tail is aligned with the non polar hydrocarbon tail of the cholesterol so its motion is unaffected.
Explain the paradoxical effects of cholesterol in phospholipid bilayers
Cholestrol descrease fluidity of the bilayer by reducing phospholid chain motion but also increases fluidity of the bilayer by reducing phospholid packing.
What is the functional evidence for proteins in membranes?
- Facilitated diffusion
- Ion gradients
- specificity of cell responses
What are the biochemical evidence for protein s in membranes?
- Membrane fractionation + gel electrophoresis
- Freeze Fracture
What can be used to make the membrane fractionation+ gel electrophoresis?
SDS-Polyacrylamide gel electrophoresis (SDS-PAGE)
Describe how freeze fracture works
Cell is frozen in water and then fractured with a knife to produce an E fracture face and a P fracture face.
What are the three modes of motion permitted for proteins?
Conformational change
Rotational
Lateral
What mode of action is not permitted for proteins? And why?
Flip-flop because it is not thermodynamically favourable.
