Chapter 13- Lipids and Membranes

Question 1

What are the 5 functions of biological membranes?

Answer 1

CITCE 
compartmentalisation
intercellular interaction
transport
communication
energy transduction

Question 2

Most membrane lipids are amphipathic, what does this mean?

Answer 2

They have a polar end and a non polar end.

Question 3

What are the the simplest lipids, and what are they composed of?

Answer 3

fatty acids. A hydrocarbon chain with a carboxylic acid

Question 4

What phases can lipids exist in?

Answer 4

crystal, fluid, gel?

Question 5

Which enzyme catalyses lipid flip-flip- transverse diffusion?

Answer 5

flippase

Question 6

Name the 3 spontaneous assemblies that lipids assemble into?

Answer 6

micelle, bilayer, liposome

Question 7

What are the driving forces for lipid self assembly?

Answer 7

entropic and enthalpies forces

Question 8

What type of bonds hold lipid membranes?

Answer 8

non-covalent bonds.

Question 9

What are 2 ways to avoid phase changes?

Answer 9

1. Cholesterol/ sterols (long, staurated chain) or membranes would crystallise at physiological temp
2. mitochondrial membrane doesn’t have cholesterol but has many phospholipids with double bonds- kinks= hard to pack and crystallzize= lower the melting point

Question 10

What 3 things influence membrane fluidity?

Answer 10

1. fatty acid chain length
2. saturated (double bonds- kinks)
3. presence of sterols

Question 11

what is the purpose of FRAP, and what does it stand for?

Answer 11

to measure lipid lateral diffusion. Flourescence recovery after photobleaching

Question 12

Sterols are fluidity buffers, explain what they do at low and high temp?

Answer 12

@low temp- the prevent tail from interaction= ^ fluidity

@high temp- they restrict phospholipid movement= less fluid

Question 13

How do amphibians adapt cold temperatures?

Answer 13

Add doubles and cholesterol.

Question 14

What are lipid rafts?

Answer 14

Cholesterol + sphingolipids in the plasma membrane. they separate from glycerophospholipids.

Question 15

Why are lipid rafts isolated?

Answer 15

because they are resistant to detergent solubilisation.

Question 16

Why is it easy to pack lipid rafts?

Answer 16

The sphingolipid has no double bonds.

Question 17

What are caveolae?

Answer 17

invaginated lipid raft domain of plasma membranes.

Question 18

How do peripheral proteins associate to the membrane?

Answer 18

non covalently .

Question 19

How can you dislodge peripheral proteins ?

Answer 19

change in pH, extract with salt, or chelators.

Question 20

How can you dislodge integral proteins?

Answer 20

they must be solubilised with detergent.

Question 21

What is special about the picket fence model?

Answer 21

It restricts lateral diffusion of lipids, They have to stay within the fence.

Question 22

When try to isolate and study membrane proteins, explain ionic/ non-ionic detergents?

Answer 22

ionic detergents- denature proteins (SDS, CTAB, DOC)

non-ionic detergents, don’t denature proteins (TritonX-100, ocytylglucoside)

Purified proteins can be made into liposomes for study.

Question 23

Amphipathic detergents are used to solubilize integral proteins. Explain how it works?

Answer 23

The hydrophobiic parts simulate the lipids, the polar parts simulate the hydrophilic head and interact with water.

Question 24

What happens if the amphipathic detergent I removed from the integral protein solubilisation?

Answer 24

The proteins will aggregate and come out of solution.