Lipid Movement

Question 1

What are the 3 ways that lipids move within the bilayer?

Answer 1

1. Rotational
2. Lateral
3. Transverse

Question 2

Describe rotational

Answer 2

• The spinning of a lipid around its axis

- Does not alter its position but affects its interaction with neighbouring molecules

Question 3

Describe lateral

Answer 3

• Neighbouring lipids exchange places

- It allows lipids to change position within a bilayer leaflet

Question 4

Describe transverse

Answer 4

• The exchange of molecules (lipids or proteins) between leaflets
• Can move across a bilayer membrane

Question 5

What does transverse require?

Answer 5

Energy

Question 6

Why don’t most large proteins flip flop?

Answer 6

Due to their polar regions which are unfavourable in the hydrophobic core of the bilayer

Question 7

Why is transverse movement a fairly slow process?

Answer 7

Requires a significant amount of energy for ‘flip-flopping’

Question 8

How are proteins involved in transverse movement?

Answer 8

Lipid translocation can be mediated by proteins

Question 9

What do P-type flippases carry out?

Answer 9

Inward movement of lipids

Question 10

What do ABC proteins mediate?

Answer 10

Outward movement of lipids

Question 11

What do scramblases perform?

Answer 11

Non-specific Ca2+ dependent randomisation of lipids across the bilayer

Question 12

What is function of scramblases?

Answer 12

• Randomise the normal membrane distribution of head groups and undo the work of translocases
• Allow amino phospholipids to get from inner side of membrane

Question 13

How are scramblases controlled?

Answer 13

Switched on/off under special circumstances (when platelet is activated, when sperm fertilises egg, apoptosis)

Question 14

At ambient temperatures, why are lipids in membranes mobile?

Answer 14

Due to ability of lipids to move laterally and rotationally without much energy needed

Question 15

Why is energy needs for phospholipids to move transversely?

Answer 15

Due to negative charge