1. The Memrane Bilayer: Main Biophysical Properties

Question 1

What is the general membrane dry weight composition?

Answer 1

Protein - 60%
Lipid - 40%
Carbohydrate - 1-10%

Question 2

What % of total membrane weight is water?

Answer 2

20%

Question 3

What are amphipathic molecules?

Answer 3

Molecules with both a hydrophilic and hydrophobic moiety

Question 4

What is the general structure of a phospholipid?

Answer 4

• 1 glycerol
• 2 fatty acids
• phosphate
• head group

Question 5

What are the most prevelant carbon chains in a phospholipid?

Answer 5

C16 & C18

Question 6

Why do phospholipids have a kink?

Answer 6

They contain a cis double bond

Question 7

What is the typical carbon chain length range for a phospholipid?

Answer 7

C14 - C28

Question 8

What head group does sphingomyelin contain?

Answer 8

phosphocholine head

Question 9

What head group does a glycoprotein contain?

Answer 9

Sugar

Question 10

What are the two types of glycoproteins?

Answer 10

• Cerebrosides

- Gangliosides

Question 11

What head group does a cerebroside contain?

Answer 11

sugar monomer

Question 12

What head group does a ganglioside contain?

Answer 12

Oligosaccharide (sugar multimer)

Question 13

What are the 2 types of membrane structure?

Answer 13

• Lipid micelle (circle with heads facing out and tails in)

- Lipid bilayer (2 layers with heads facing out and tails in)

Question 14

What are the 4 phospholipid motions?

Answer 14

• Flexion
• Rotation
• lateral diffusion
• flip flop

Question 15

How does the cis double bond influence the bilayer structure?

Answer 15

Reduces the phospholipid packaging, so membrane is more permeable to substances

Question 16

What is the role of cholesterol in the membrane?

Answer 16

To stabilise the membrane to prevent fracturing

Question 17

What are the 4 types of membrane?

Answer 17

• Phospholipids
• Glycoproteins
• Sphingomyelin
• Cholesterol

Question 18

What is the structure of cholesterol?

Answer 18

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

Question 19

How does cholesterol stabilise the membrane?

Answer 19

Reduces the influence of external factors that can alter the structure and/or fluidity of the membrane by abolishing the endothermic phase change during heating of the phospholipid by preventing the membrane from going into its crystaline state and from becoming too fluid

Question 20

How is cholesterol inserted into the phospholipid bilayer?

Answer 20

Carbonyl oxygen on the fatty acid side chain hydrogen bonds to the hydroxyl group on the polar head group of the cholesterol

Question 21

What are the effects of cholesterol insertion in phospholipid bilayers?

Answer 21

Reduces fluidity - Reduces phospholipid chain motion by attaching a rigid structure to it
Increases fluidity - reduces the phospholipid packaging by increasing the distance between each phospholipid

Question 22

What are the general functions of biological membranes?

Answer 22

• Highly selective permeable barrier
• Communication
• Signal generation in response to a stimuli
• Control of enclosed chemical environment
• Recognition (signaling molecules): adhesion proteins & immune surveillance

Question 23

Are all membranes the same?

Answer 23

No each has a different structure and therefore a different function
e.g. secretion, transportation, absorption of biody fluids, etc.