Membrane structure

Question 1

Do phospholipids spontaneously flip-flop in membranes?

Answer 1

no, they need ATP driven Flippase catalyzes flip-flop

Question 2

Where are lipids synthesized?

Answer 2

endoplasmic reticulum

Question 3

What are the three classes of lipids?

Answer 3

phospholipids, sphingolipids, and cholesterol

Question 4

What is the structure of cholesterol?

Answer 4

a polar hydroxyl group, rigid steroid ring group, and a hydrocarbon tail

Question 5

What does cholesterol do when it’s in a lipid?

Answer 5

• the steroid ring interacts with the hydrophobic tail of other phospholipids and immobilizes the lipid and decreases fluidity
• lipids are forced to be straightened by cholesterol
• membrane thickness depends on the amount of cholesterol

Question 6

Does the ER or Golgi have the thicker membrane? Why?

Answer 6

Golgi has the thicker membrane because it has more cholesterol

Question 7

What does cholesterol uptake depend upon?

Answer 7

• low-density lipoprotein receptor (LDLR)

Question 8

There is a _________ for cholesterol production.

Answer 8

negative feedback

Question 9

What is the first and rate-limiting enzyme is synthesizing cholesterol?

Answer 9

HMGCoA - statins block this step

Question 10

What protein regulates both the LDLR and all 30 of the synthesis proteins?

Answer 10

sterol regulatory element binding protein (SREBP) that holds the transcription factor a basic helix loop helix (bHLH) DNA binding protein

Question 11

What happens when cholesterol is low?

Answer 11

• Insig no longer binds to SCAP and the SCAP/SREBP complex gets packaged into vesicles to go to the Golgi
• Two step proteolysis (RIP - regulated intramembrane proteolysis) S1P and S2P cut bHLH and it goes to the nucleus (cleavage required by both)

Question 12

What is RIP been shown critical for?

Answer 12

Notch signaling in development and for cleavage of amyloid precursor protein (APP) to produce the beta amyloid peptide in Alzheimer’s disease

Question 13

What percentage of ATP energy does Na-K ATPase use?

Answer 13

30%