ICPP S2 - Membrane Bilayer

Question 1

What are the functions of a Biological Membrane?

Answer 1

• Highly selective permeability barrier
• Recognition, signalling and immune surveillance.
• Electrical and Chemical signal generation.
• Communication.
• Control what goes in and out - controlling the intracellular environment.

Question 2

How many different domains of the plasma membrane have different functions?

Answer 2

• Basal domain - interacts with basement membrane.

- Lateral domain - interacts with adjacent cells.

Question 3

What may the different functions of different regions of the plasma membrane be?

Answer 3

• Fluid absorption
• Secretion and transport
• Synapsing- nerve junction
• Electrical signal conduction
• Changing physical shape of the cell.

Question 4

What is the membrane composition in terms of dry weight?

Answer 4

• 40% lipid
• 60% protein
• 1-10% carbohydrate

These figures are estimate

Question 5

Why does actual membrane composition differ from dry composition?

Answer 5

Membranes are hydrates structures and 20% of their weight is water.

Question 6

Membrane lipids are amphipathic, what does this mean?

Answer 6

Contain both hydrophilic and hydrophobic moieties/ regions.

Question 7

Give 4 different head groups a phospholipid may have?

Answer 7

• Choline
• Amines
• Amino acid
• Sugars

Question 8

What is phosphatidylcholine?

Answer 8

A phospholipid with choline as its head group - major constituent of cellular membranes.

Question 9

What is sphingomyelin?

Answer 9

A type of sphingolipid which commonly occurs in the membranes of Schwann cells.
Form the myelin sheath that surround nerve cell axons.

Question 10

What is a glycolipid?

Answer 10

A lipid with a sugar head group.

Question 11

What is the difference between a cerebroside and a ganglioside?

Answer 11

A cerebroside head group is a sugar monomer, whereas a ganglioside head group is an oligosaccharide.

Question 12

What is an oligosaccharide?

Answer 12

A polymer of a small number of simple sugars, aroun 3-12.

Question 13

What are the four modes of motion of a phospholipid?

Answer 13

Flexion - movement of the fatty acid legs.
Rotation
Lateral diffusion
Flip-flop

Question 14

What are the 3 distinct structural groups in cholesterol?

Answer 14

• Polar head group - Hydroxyl group
• Rigid sterol group - rings
• Non-polar hydrocarbon chain

Question 15

What are cholesterol’s effects of membrane fluidity?

Answer 15

Reduces membrane fluidity at normal temperatures and reduces phospholipid movement.
At low temperatures in keeps the membrane fluid by disrupting packing of phospholipid.
At high temperatures it allows for the membrane bilayer to maintain integrity.

Question 16

How is cholesterol integrated into the bilayer?

Answer 16

The polar OH group of the cholesterol forms a hydrogen bond with the electronegative O in the ester bond, between the fatty acid chain and glycerol of the phospholipid.

Question 17

How does cholesterol have a paradoxical effect in membrane bilayer?

Answer 17

• Rigid sterol ring adds rigidity and reduced fluidity to the bilayer.
• Spacing between the phospholipid molecules that cholesterol creates increases the fluidity of the bilayer.