Lecture 3: Physical Properties of Lipids

Question 1

What are the 5 physical properties of cell membranes?

Answer 1

surface charge, fluidity, width, curvature, lateral pressure

Question 2

describe 5 differences between the ER membrane and PM

Answer 2

1) ER has lots of unsaturated phospholipids
2) ER is not well packed
3) PM has negatively charged membrane
4) PM is thicker
5) Proteins at the ER supposedly have shorter transmembrane domains

Question 3

how is the ER a biogenic membrane?

Answer 3

it synthesises new lipids

Question 4

what % of phospholipids are anionic?

Answer 4

30%

Question 5

why is charge important for protiens and lipids?

Answer 5

for electrostatic interactions that can determine membrane associations

Question 6

What does MARCKs do?

Answer 6

stabilise interactions with the membrane via polybasic stretch of amino acids. the membrane association is regulated by calcium ions and calmodulin and protein phosphorylation in the polybasic region

Question 7

what factors affect membrane fluidity?

Answer 7

length of acyl chain, saturation of acyl chain, cholesterol, temperature

Question 8

what is the effect of longer hydrocarbon chains?

Answer 8

more van der vaals so more rigid than shorter chains

Question 9

what is the effect of saturated hydrocarbon chains?

Answer 9

they are straight, well packed so more rigid than double bonds

Question 10

what is the effect of cholesterol in the membrane?

Answer 10

can make sphingolipids more fluid but can rigidify membranes too

Question 11

How does cholesterol interact with the membrane?

Answer 11

ring structure interacts with the first few carbons of the lipid tails. has a small OH head group so is triangle shaped

Question 12

what happens to the acyl chains of E.coli grown at high temps?

Answer 12

higher degree of acyl chain saturation

Question 13

what have experiments shown in response to changing temperatures?

Answer 13

changing lipid composition

Question 14

What is DesK and what organism is it present in?

Answer 14

Thermosensing histidine kinase, B. subtilis

Question 15

Explain how the membrane of B. subtilis is remodelled in response to temperature.

Answer 15

DesK is usually inactive so won’t phosphorylate the TF DesR. when temps decrease, the membrane becomes more rigid, packing closer and the transmembrane domains become more straight so the kinase domain becomes active as is free from autoinhibition. it activates DesR which causes the transcription of a gene encoding deltaS desaturase which desaturates the phospholipid chains and increases fluidity. this causes autoinhibition of DesK kinase domains again.

Question 16

Give an example of membrane fluidity allowing intermolecular interactions

Answer 16

EGFR dimerisation upon ligand binding

Question 17

what don’t form bilayers by themselves?

Answer 17

non-bilayer lipids

Question 18

what do all membranes contain at least one of?

Answer 18

non-bilayer lipid

Question 19

what shape can non-bilayer lipids form when pure?

Answer 19

cone or wedge

Question 20

what are micelles and why are they thermodynamically stable?

Answer 20

all the hydrophobic tails point inwards in a sphere

Question 21

what is an inverted micelle?

Answer 21

the hydrophobic tails point outwards so isn’t thermodynamically stable

Question 22

what are the possible functions of non-bilayer lipids?

Answer 22

membrane fusion, fission, packing properties, membrane curvature

Question 23

how can non-bilayer lipids affect the packing properties?

Answer 23

they have small head groups so other proteins more likely to be able to fit between them for higher packing density and lateral pressure

Question 24

Explain how PKC is activated

Answer 24

phospholipase cleaves PIP2 to DAG, releasing IP3 causing release of Ca ions from the ER. this causes PKCBII to translocate to the cell membrane. Ca binds regions of its C2 domain to mediate bridging bridging to the phosphates. Binding of DAG to C1A domain causes C1A disengagement and a pseudosubstrate is removed from the catalytic cleft. Binding of DAG to C1B domain results in downstream signalling

Question 25

how may non-bilayer lipids in a local concentration influence membrane curvature?

Answer 25

can cause negative and positive curvature

Question 26

Why are flippases essential?

Answer 26

for assembly and regulation of the membrane in PM, golgi and endosomes and maintain the asymmetric transbilayer distribution

Question 27

What does the exoplasmic leaflet of the bilayer have that makes it inert?

Answer 27

Cholesterol and PC

Question 28

where can phospholipids freely flip flop with no ATP?

Answer 28

from the ER to the cis golgi

Question 29

what could PLD derived phosphatidic acid do?

Answer 29

induce negative curvature on the inner leaflet

Question 30

What could ATP driven local translocation of lipids do?

Answer 30

help create high local conc of aminophospholipid on the cytosolic leaflet favourable for recruitment of clathrins, and ARF for example.