Membrane Structure

Question 1

What are the molecular components of the membrane?

Answer 1

lipids (lipid bilayer)
carbohydrates (usually on extracellular domains of lipids or proteins)
proteins (30% of encoded proteins are membrane-associated

Question 2

Explain the concept of membrane fluidity

Answer 2

phospholipids diffuse rapidly (10^7times/sec)

• several mm/s @ 37C
• do not spontaneously flip-flop (need ATP driven flipase)

Question 3

What are the parts of a phospholipid?

Answer 3

Diglyceride
Phosphate group
Choline

Question 4

What are the parts of a sphingolipid?

Answer 4

long
charged
have amine
- may have sugar

Question 5

What are the parts of a cholesterol?

Answer 5

Polar hydroxyl group
Rigid steroid ring group
Hydrocarbon tail

Question 6

How are membrane bilayers asymmetric?

Answer 6

carbohydrates on extracellular side
- non-uniform distribution of lipids/ proteins
more - phosphipids (PS, PE, PI) on inside of membrane
PC, sphingomyelin, glycolipids on outside

Question 7

What are the different ways proteins can associate with membranes?

Answer 7

Transmembrane (x 1, x>1, cylinder)
Intra/extracellular (self-anchored, lipid anchored, oligosaccaride linked, monocovalent interaction with another protein)

Question 8

How is cholesterol synthesis regulated?

Answer 8

SYNTHESIS
~30 enzymes
Statins: blick first step- HMGCoAreductase

UPTAKE

• negative feedback loop
• depends on LDLR
• enough through diet -> decrease synthesis

BOTH
- SREBP: regs LDLR and all synth enzymes

Question 9

What is the function of proteins in the membrane?

Answer 9

Control the movement of molecules between the inside and outside of the cell

Question 10

What does membrane fluidity depend on?

Answer 10

composition and temperature

Question 11

What are the characteristics of phospholipids? Examples?

Answer 11

amphipathic (hydrophilic & hydrophobic)
Phosophatidylethanolamine (PE)
Phosphastidylcholine (PC)
Phosphatidylserine (PS)
Phosphatidyllinositol (PI)
- derived from glycerol

Question 12

How do cholesterols interact with other lipids?

Answer 12

interaction of ring and other lipids’s tails immobilize - decreases fluidity

tails are straightened by cholesterol - > membrane thickness

Question 13

Where does cholesterol come from?

Answer 13

ingestion/ uptake

synthesis by the liver

Question 14

What is SCAP?

Answer 14

SREBP cleavage activating protein

Question 15

What is Insig

Answer 15

cholesterol regulating protein

Question 16

What happens when cholesterol is high?

Answer 16

Insig binds SCAP-> blocks signaling

Question 17

What happens when cholesterol is low?

Answer 17

SCAP binds SREBP -> goes to golgi -> bHLH released from SREBPby RIP (regulated intramembrane proteolysis) ->cleaved by S1P & S2P-> bHLH moves into nucleus -> binds promoters, activates genes to produce LDLRs & increase enzymes involved in cellular synthesis of cholesterol

Question 18

How do some bacteria disrupt the cell membrane?

Answer 18

secrete toxins that create pores -> rupture membranes (staphlococcus aureus, listeria monocytogenes)