M&R Session 1

Question 1

State the weight composition of membranes when dehydrated

Answer 1

40% Lipid
60% Protein
1-2% Carbohydrate

Question 2

What percentage weight of a cell membrane is water when hydrated?

Answer 2

20%

Question 3

What are the four components of a phospholipid?

Answer 3

Glycerol backbone
2 fatty acids (identical or different)
Phosphate
Head group

Question 4

What type of lipid is sphingomyelin?

What moiety has been replaced?

Answer 4

Glycolipid

Phosphocholine moiety has been replaced with a sugar

Question 5

What are the two types of glycolipid?

How do they differ?

Answer 5

Cerebrosides = sugar monomer head group
Gangliosides = oligosaccharide head group

Question 6

What are the four types of phospholipid motions? (Demonstration optional)

Answer 6

Flexion
Rotation
Lateral diffusion
Flip flop

Question 7

What characteristic differentiates saturated from unsaturated hydrocarbons

What effect does this have?

Answer 7

Unsaturated have a cis double bond

Reduces phospholipid packing

Question 8

What are three characteristics of cholesterol?

Answer 8

Polar head group
Rigid planar steroid ring structure
Non-polar hydrocarbon tail

Question 9

Increasing molarity of cholesterol has what effect on phospholipid bilayers?

Answer 9

Decreases endothermic phase transition

Question 10

State the two effects of cholesterol on phospholipids (hint: paradoxical)

Answer 10

Reduced chain motion (rigid) -> reduced fluidity

Reduced packing -> increased fluidity

Question 11

Give you functional and one biochemical evidence of proteins in membranes

Answer 11

Functional
Facilitated diffusion
Ion gradients
Specificity of cell responses

Biochemical
Freeze fracture
Membrane fractionation + gel electrophoresis

Question 12

What motion is not feasible for proteins?

Answer 12

Flip flop

Question 13

In what ways can membrane protein mobility be restricted?

Answer 13

Aggregates
Tethering
Interactions with other cells
Association with extra membranous proteins (peripheral)
Proteins separate to fluid phase and cholesterol poor regions

Question 14

Compare and contrast peripheral to integral proteins

Answer 14

Peripheral Integral
Bound to surface Interact with hydrophobic
Regions of lipid bilayer
Electrostatic and hydrogen bonds
Removed by changes Removed by agents competing
In pH and ionic strength For non polar interactions

Question 15

Give three general functions of a cell membrane

Answer 15

Continuous, highly selective permeability barrier
Control of enclosed chemical environment
Communication
Recognition
Signal Generation