MNE- Cholesterol Synthesis & Lipid Transport Exam Solutions Manual
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Module
MNE- Cholesterol Synthesis & Lipid Transport
Institution
MNE- Cholesterol Synthesis & Lipid Transport
MNE- Cholesterol Synthesis & Lipid Transport Exam Solutions Manual
What molecule is the central starting material for cholesterol synthesis? - Answers Acetyl-CoA
Describe the structure of cholesterol (6 points) - Answers a) 27 Carbons (all from acetyl-CoA
b) Three 6-C rings, one 5-C ring
c) An ...
MNE- Cholesterol Synthesis & Lipid Transport Exam Solutions Manual
What molecule is the central starting material for cholesterol synthesis? - Answers Acetyl-CoA
Describe the structure of cholesterol (6 points) - Answers a) 27 Carbons (all from acetyl-CoA
b) Three 6-C rings, one 5-C ring
c) An 8-C side chain at C17
d) Composed of isoprene units
e) 3' OH group is the only oxygen (*hydrophobic*
f) Double bond between C-5 & C-6 (delta-5)
What are three classes of compounds that isoprenes are precursors for? - Answers 1) Vitamins
2) Cholesterol
3) Steroid hormones
What are the 5 intermediate substrates during cholesterol synthesis? - Answers 1) Acetyl-CoA
2) Mevalonate
3) Isopentenyl Pyrophosphate
4) Squalene
5) Cholesterol
What are the 3 steps of cholesterol synthesis up to mevalonate? Why is this important - Answers 1) 2
acetyl-CoA --> acetoacetyl-CoA
2) A third acetyl-CoA added --> *HMG-CoA*
3) HMG-CoA --> mevalonate
a) 2 NADPH --> NADP+
b) carboxyl group reduced to OH
c) CoA Released
HMG-CoA --> mevalonate is a major regulatory step for cholesterol synthesis: *inhibited by statins*
, How do statins work in the cholesterol biosynthetic pathway? - Answers Resemble mevalonic acid, so
they competitively inhibit HMG-CoA Reductase
What are the 3 steps of cholesterol synthesis after mevalonate? - Answers 1) activated isoprenes made
by 3 sequential phosphorylations & 1 decarboxylation
a) yields d3-isopentenyl PPi + dimethylallyl PPi
b) 2 Pi added to C-5
c) Pi added at C-3, immediate decarboxylation of C1
d) Removal of C3 phosphate
2) Formation of Squalene
a) isoprenes fuse to form geranyl PPi
b) another isoprene added to form farnesyl PPi
c) 2 farnesyl PPi + NADPH --> Squalene
3) Conversion of Squalene to cholesterol
a) squalene - lanosterol - cholesterol (humans)
b) squalene - stigmasterol (plants)
c) squalene - ergosterol (fungi, yeast)
How is cholesterol stored within cells and transported in the blood? - Answers Within cells: fatty acyl-
CoA + cholesterol --> *cholesterol ester* via ACAT (Acyl-CoA-cholesterol acyl transferase)
In the circulation: cholesterol + Lecithin (PC) --> *cholesterol ester* via LCAT (lecithin-cholesterol acyl
transferase), transported via HDLs
What are ACAT and LCAT? - Answers Enzymes that convert cholesterol to cholesterol esters.
ACAT: Acyl-CoA-cholesterol Acyl Transferase (stores in cells)
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