Membrane Structures say whhuuuhh?

Question 1

3 types of lipids

Answer 1

1. phosphoglycerides
2. sphingolipids
3. cholesterol

(4) glycolipids

Question 2

4 types of phosphoglycerides

Answer 2

1. PE
2. PC
3. PS
4. PI

Question 3

Which phosphoglycerides are found on the cytoplasmic leaflet?

Answer 3

Phosphatidyl serine (PS)
Phosphatidyl inositol (PI)
Phosphatidyl ethanolamine (PE)
Cholesterol

Question 4

Which phosphoglycerides are found on the exoplasmic leaflet?

Answer 4

Phosphatidyl choline
sphingomyelin
glycolipids
choesterol

Question 5

What are two ways that cholesterol is gained?

Answer 5

1. ingestion/uptake

2. synthesis by liver

Question 6

Ingestion/uptake of cholesterol depends on what receptor?

Answer 6

low density lipoprotein receptor

Question 7

What is the rate limiting enzyme in the cholesterol synthesis pathway in the liver?

Answer 7

HMG CoA

Question 8

What drug is used to lower cholesterol? Why do we care?

Answer 8

Statin: most prescribed drug in the country

-lower heart attack risk

Question 9

explain steps in cholesterol synthesis

Answer 9

1. When cholesterol is low: Insig dissociates from SCAP-SREBP complex.
2. SCAP escort SREBP (and BHLH) to golgi by vesicular transport
3. bHLH is released from SREBP by 2 step proteolysis
4. bHLH txn factor moves to nucleus –> binds to DNA promotors
   - ->activates genes to produce more LDLR to bring cholesterol into the cell and increase all enzymes involved in cellular synthesis of cholesterol

(depends on ~30 proteins)

Question 10

When does Insig bind SCAP-SREBP complex?

Answer 10

when cholesterol levels are high, to block SCAP signaling

Question 11

Explain how bHLH is released from SREBP

Answer 11

Released through Regulated intramembrane proteolysis (RIP)

• cleavage of bHLH from SREBP by BOTH
  SIP (luminal) and S2P (w/in membrane)

Question 12

If cell is to undergo cell death, which lipids will appear on extracellular bilayer?

Answer 12

PE, PS, PI —–> signals macrophages to engulf/apoptosis