Session 1 - Lipids, Proteins + Membrane Structure

Question 1

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

Answer 1

• 40% Lipid
• 60% protein
• 1-10% Carbohydrate

Question 2

Describe the structure of a phospholipid molecule

Answer 2

Head group - range of polar molecules (aa’s, choline so, amines and sugars)
Fatty acid “tail” - Lots of variety (C16+18 most common), unsaturated, cis double bond creates a kink in chain

Question 3

What are Glycolipids?

Answer 3

Sugar containing lipids

Question 4

What is Sphingomyelin?

Answer 4

Only phospholipid not based on glycerol (when in membrane is very similar to others)

Question 5

What are Cerebrosides?

Answer 5

Glycolipid with sugar monomers as head groups

Question 6

What are Plasmalogens?

Answer 6

Non-classical Phospholipids

Question 7

What are Gangliosides?

Answer 7

Glycolipids with sugar oligosaccharides for head groups

Question 8

What does the distribution of lipids in the mebrane depend on?

Answer 8

Tissue type and function

Question 9

What two structures do Amphipathic molecules readily form in water?

Answer 9

Micelles and Bilayers

Question 10

What forces and between what regions drive Bilayer formation?

Answer 10

Vdws between the hydrophobic fatty acid chains

Question 11

Name the four ways that lipids can move in a membrane?

Answer 11

• intra-chain motion
• Axial rotation
• Lateral diffusion along same plane
• Flip-Flop

Question 12

Name the ways membrane proteins can move?

Answer 12

• Lateral movement
• Rotation
• Conformational change

Question 13

What restricts membrane protein movements?

Answer 13

• Cholesterol levels in particular region
• Associations with other membrane proteins
• Association with extra-membranous proteins (e.g cytoskeleton)

Question 14

How do Peripheral proteins bind to the membrane and how can they be removed?

Answer 14

• Electrostatic forces and H-bonds

- pH changes or Ionic strength changes

Question 15

How are integral membrane proteins bound to the membrane and how can they be removed?

Answer 15

• Interact with hydrophobic region of bilayer

- Agents that compete for hydrophobic interactions (e.g detergents, organic solvents)

Question 16

How is membrane protein synthesis different to secretory protein synthesis?

Answer 16

The protein has to span the membrane not sit solely within it

Question 17

How does a membrane protein achieve its spanning of the membrane in its synthesis?

Answer 17

Through the addition of a stop transfer signal which is a highly hydrophobic chain of around 20 aa’s

Question 18

What are Hydropathy plots used for?

Answer 18

To see how many transmembrane regions a protein has

Question 19

Why is membrane asymmetry important?

Answer 19

Important for biological function

I.e Ensure receptors are situated on the same side of the membrane that their substrate will be

Question 20

Why is the “kink” in the FA chain important?

Answer 20

It decreases phospholipid packing and hence increases fluidity of the membrane

Question 21

How does cholesterol increase packing in the membrane?

Answer 21

Forms H-bonds with FA chain

Question 22

How does cholesterol decrease membrane fluidity?

Answer 22

Decreases the packing by being a physical barrier between chains

Question 23

What is protein lateral diffusion affected by?

Answer 23

• Size
• Aggregation
• Association with other proteins (intra or extracellular)
• Amount of cholesterol in near vicinity

Question 24

What is the erythrocyte cytoskeleton composed of and why is it important?

Answer 24

Spectrin and Actin

Maintains shape of RBCs

Question 25

How does the cytoskeleton attach to the membrane?

Answer 25

Ankyrin and Glycophorin
Bound to
Band 3 and Band 4.1 respectively

Question 26

What are Haemolytic anaemias in general?

Answer 26

RBCs become spherical and are therefore subject to increased lysis due to shearing forces of capillary beds

Question 27

What is Hereditary Spherocytosis?

Answer 27

Spectrin levels depleted, RBCs round up, leads to increased lysis
Bone marrow cannot compensate and hence a haemolytic anaemia results

Question 28

What are Amphipathic molecules?

Answer 28

Molecules with both Hydrophobic and Hydrophilic moieties

Question 29

What is Hereditary Elliptocyosis?

Answer 29

Spectrin molecules are unable to form heterotetramers, RBCs form elliploid shape (rugby ball) and a Haemolytic anaemia results