1.1 The Membrane Bilayer

Question 0

What is the composition of the dry weight of the membrane?

Answer 0

40% lipid
60% protein
1-10% carbohydrate

Question 1

What are the five main functions of membranes?

Answer 1

• continuous, highly selective permeability barrier
• control of the enclosed chemical environments
• communication
• recognition
• signal generation in response to stimuli

Question 2

What are amphipathic molecules?

Answer 2

Have hydrophilic and hydrophobic regions

Question 3

What is the structure of a phospholipid?

Answer 3

Glycerol backbone
Very long fatty acid chains
Small head group

Question 4

What are the four different head groups?

Answer 4

Choline
Amines
Amino acids
Sugars

Question 5

The fatty acid chains are roughly the same length. What is the advantage of this?

Answer 5

The bilayer will be roughly the same thickness all the way along

Question 6

What are the features of sphingomyelin?

Answer 6

Not based on glycerol but resembles other phospholipids

Has a phosphate group and a fatty acid chain

Question 7

What are the two classes of glycolipids?

Answer 7

Cerebroside - glycolipid with single carbohydrate

Ganglioside - glycolipid with complex carbohydrates

Question 8

Describe bilayer formation

Answer 8

When phospholipids are put in water the Van Der Waals attraction between the hydrophobic tails drives formation of a bilayer

Question 9

What forces maintain the bilayer structure?

Answer 9

Hydrogen bonds between hydrophilic moieties
Interactions between the hydrophilic groups and water
Electrostatic attractions

Question 10

What are the four different motions of phospholipids?

Answer 10

Flexion = vibration
Rotation
Lateral diffusion
Flip-flop

Question 11

How do the cis double bonds between fatty acid molecules create fluidity?

Answer 11

Reduce phospholipid packing by separating the phospholipid molecules

Question 12

What are the modes of motion of proteins in the bilayer?

Answer 12

Conformational change
Rotational
Lateral

Question 13

What restricts the mobility of the membrane?

Answer 13

Lipid mediated effects
Membrane protein associations
Extra-membranous protein association - e.g. Cytoskeleton

Question 14

What is the importance of cholesterol in the plasma membrane?

Answer 14

Stabilises the plasma membrane as it’s presence means less energy is needed to melt the crystalline phospholipid into fluid membrane
Binding reduces motion of the membrane but increases space between phospholipid molecules so overall increases fluidity