PHAR 505 EXAM 2 - QUESTIONS AND ANSWERS | 2026 UPDATE | WITH COMPLETE
SOLUTIONS.
What lipoprotein is described in the lecture as causally linked to atherosclerotic cardiovascular disease?
- (answer)LDL.
What happens when LDL accumulates in vessel walls? - (answer)Lipid accumulation and inflammation
promote formation of atherosclerotic plaque.
Why should circulating LDL be kept low? - (answer)Because both the magnitude and duration of LDL
exposure increase ASCVD risk.
What are the three major sources or fates emphasized for cholesterol homeostasis? - (answer)Import
from diet, synthesis in cells, and oxidation to bile acids.
What is the basic building block of cholesterol biosynthesis? - (answer)The isoprene unit, a C5
hydrocarbon skeleton.
What are isoprenoids? - (answer)Linear compounds made of repeating C5 isoprene units.
What are terpenoids? - (answer)Compounds derived from the same C5 unit that can be oxidized,
cyclized, and rearranged.
How many carbons does cholesterol contain? - (answer)27 carbons.
How is cholesterol made from isoprene-based precursors? - (answer)C5 subunits are stitched together
to form a C30 precursor, then 3 carbons are removed to yield cholesterol.
What major structural class does cholesterol belong to? - (answer)Steroids.
What is the steroid framework of cholesterol? - (answer)Three fused 6-membered rings and one fused
5-membered ring.
,PHAR 505 EXAM 2 - QUESTIONS AND ANSWERS | 2026 UPDATE | WITH COMPLETE
SOLUTIONS.
What does alpha mean in steroid nomenclature? - (answer)A substituent below the plane of the
molecule.
What does beta mean in steroid nomenclature? - (answer)A substituent above the plane of the
molecule.
What ring conformations are common in steroids? - (answer)Chair and boat conformations.
How do hydroxyl groups affect steroid properties? - (answer)They make steroids more hydrophilic.
How do ketones affect steroid properties relative to hydroxyl groups? - (answer)Ketone-containing
steroids are often more hydrophobic.
What is the starting precursor for cholesterol biosynthesis? - (answer)Acetyl-CoA.
Where does acetyl-CoA come from according to the lecture? - (answer)Fatty acid breakdown in
mitochondria and sugar breakdown through glycolysis.
How many acetyl-CoA molecules are linked to form HMG-CoA? - (answer)Three.
What enzyme converts HMG-CoA to mevalonate? - (answer)HMG-CoA reductase.
What kind of reaction does HMG-CoA reductase catalyze? - (answer)Reduction of a thioester to a
primary alcohol.
What reducing agent is used by HMG-CoA reductase? - (answer)Two molecules of NADPH.
What is the rate-limiting step in cholesterol biosynthesis? - (answer)Conversion of HMG-CoA to
mevalonate by HMG-CoA reductase.
,PHAR 505 EXAM 2 - QUESTIONS AND ANSWERS | 2026 UPDATE | WITH COMPLETE
SOLUTIONS.
Where is HMG-CoA reductase located? - (answer)In the ER membrane.
What is the first phosphorylation step after mevalonate formation? - (answer)Mevalonate is converted
to phosphomevalonate.
What enzyme carries out the first phosphorylation of mevalonate? - (answer)Mevalonate-5-
phosphotransferase.
What is the second phosphorylation step in the mevalonate pathway? - (answer)Phosphomevalonate is
converted to 5-pyrophosphomevalonate.
What enzyme adds the second phosphate in the mevalonate pathway? - (answer)Phosphomevalonate
kinase.
What happens after the third ATP-dependent step in the mevalonate pathway? - (answer)CO2 is
released and the C5 precursor is formed.
What C5 precursor is produced after decarboxylation of pyrophosphomevalonate? -
(answer)Isopentenyl pyrophosphate or IPP.
What enzyme converts IPP to DMAPP? - (answer)IPP isomerase.
What reaction joins IPP and DMAPP? - (answer)A head-to-tail reaction catalyzed by prenyltransferase or
farnesyl-pyrophosphate synthase.
What 10-carbon product is formed from IPP and DMAPP? - (answer)Geranyl pyrophosphate.
What 15-carbon precursor is formed next in elongation? - (answer)Farnesyl pyrophosphate.
, PHAR 505 EXAM 2 - QUESTIONS AND ANSWERS | 2026 UPDATE | WITH COMPLETE
SOLUTIONS.
Why does farnesyl pyrophosphate synthase not keep making longer and longer products? - (answer)The
active-site tunnel caps the length of molecules that can be made.
What enzyme joins two farnesyl pyrophosphate molecules head-to-head? - (answer)Squalene
synthetase.
What 30-carbon linear product is formed from two farnesyl pyrophosphate molecules? -
(answer)Squalene.
What enzyme epoxidizes squalene before cyclization? - (answer)Squalene epoxidase.
Why is squalene epoxidation important? - (answer)It makes the molecule reactive for cyclization.
What enzyme closes the rings to form lanosterol? - (answer)Lanosterol synthase.
How many rings are formed in the lanosterol synthase cascade? - (answer)Four rings.
What is the immediate steroid product formed after cyclization of the squalene-derived precursor? -
(answer)Lanosterol.
How many steps are required to convert lanosterol to cholesterol according to the lecture? - (answer)19
steps.
How many carbons are lost when lanosterol becomes cholesterol? - (answer)3 carbons.
What enzyme class catalyzes the methyl-removal reactions during lanosterol to cholesterol conversion?
- (answer)Cytochrome P450 monooxygenases.
What enzyme adds acyl chains to cholesterol to form cholesteryl esters? - (answer)Lecithin-cholesterol
acyltransferase or LCAT.
SOLUTIONS.
What lipoprotein is described in the lecture as causally linked to atherosclerotic cardiovascular disease?
- (answer)LDL.
What happens when LDL accumulates in vessel walls? - (answer)Lipid accumulation and inflammation
promote formation of atherosclerotic plaque.
Why should circulating LDL be kept low? - (answer)Because both the magnitude and duration of LDL
exposure increase ASCVD risk.
What are the three major sources or fates emphasized for cholesterol homeostasis? - (answer)Import
from diet, synthesis in cells, and oxidation to bile acids.
What is the basic building block of cholesterol biosynthesis? - (answer)The isoprene unit, a C5
hydrocarbon skeleton.
What are isoprenoids? - (answer)Linear compounds made of repeating C5 isoprene units.
What are terpenoids? - (answer)Compounds derived from the same C5 unit that can be oxidized,
cyclized, and rearranged.
How many carbons does cholesterol contain? - (answer)27 carbons.
How is cholesterol made from isoprene-based precursors? - (answer)C5 subunits are stitched together
to form a C30 precursor, then 3 carbons are removed to yield cholesterol.
What major structural class does cholesterol belong to? - (answer)Steroids.
What is the steroid framework of cholesterol? - (answer)Three fused 6-membered rings and one fused
5-membered ring.
,PHAR 505 EXAM 2 - QUESTIONS AND ANSWERS | 2026 UPDATE | WITH COMPLETE
SOLUTIONS.
What does alpha mean in steroid nomenclature? - (answer)A substituent below the plane of the
molecule.
What does beta mean in steroid nomenclature? - (answer)A substituent above the plane of the
molecule.
What ring conformations are common in steroids? - (answer)Chair and boat conformations.
How do hydroxyl groups affect steroid properties? - (answer)They make steroids more hydrophilic.
How do ketones affect steroid properties relative to hydroxyl groups? - (answer)Ketone-containing
steroids are often more hydrophobic.
What is the starting precursor for cholesterol biosynthesis? - (answer)Acetyl-CoA.
Where does acetyl-CoA come from according to the lecture? - (answer)Fatty acid breakdown in
mitochondria and sugar breakdown through glycolysis.
How many acetyl-CoA molecules are linked to form HMG-CoA? - (answer)Three.
What enzyme converts HMG-CoA to mevalonate? - (answer)HMG-CoA reductase.
What kind of reaction does HMG-CoA reductase catalyze? - (answer)Reduction of a thioester to a
primary alcohol.
What reducing agent is used by HMG-CoA reductase? - (answer)Two molecules of NADPH.
What is the rate-limiting step in cholesterol biosynthesis? - (answer)Conversion of HMG-CoA to
mevalonate by HMG-CoA reductase.
,PHAR 505 EXAM 2 - QUESTIONS AND ANSWERS | 2026 UPDATE | WITH COMPLETE
SOLUTIONS.
Where is HMG-CoA reductase located? - (answer)In the ER membrane.
What is the first phosphorylation step after mevalonate formation? - (answer)Mevalonate is converted
to phosphomevalonate.
What enzyme carries out the first phosphorylation of mevalonate? - (answer)Mevalonate-5-
phosphotransferase.
What is the second phosphorylation step in the mevalonate pathway? - (answer)Phosphomevalonate is
converted to 5-pyrophosphomevalonate.
What enzyme adds the second phosphate in the mevalonate pathway? - (answer)Phosphomevalonate
kinase.
What happens after the third ATP-dependent step in the mevalonate pathway? - (answer)CO2 is
released and the C5 precursor is formed.
What C5 precursor is produced after decarboxylation of pyrophosphomevalonate? -
(answer)Isopentenyl pyrophosphate or IPP.
What enzyme converts IPP to DMAPP? - (answer)IPP isomerase.
What reaction joins IPP and DMAPP? - (answer)A head-to-tail reaction catalyzed by prenyltransferase or
farnesyl-pyrophosphate synthase.
What 10-carbon product is formed from IPP and DMAPP? - (answer)Geranyl pyrophosphate.
What 15-carbon precursor is formed next in elongation? - (answer)Farnesyl pyrophosphate.
, PHAR 505 EXAM 2 - QUESTIONS AND ANSWERS | 2026 UPDATE | WITH COMPLETE
SOLUTIONS.
Why does farnesyl pyrophosphate synthase not keep making longer and longer products? - (answer)The
active-site tunnel caps the length of molecules that can be made.
What enzyme joins two farnesyl pyrophosphate molecules head-to-head? - (answer)Squalene
synthetase.
What 30-carbon linear product is formed from two farnesyl pyrophosphate molecules? -
(answer)Squalene.
What enzyme epoxidizes squalene before cyclization? - (answer)Squalene epoxidase.
Why is squalene epoxidation important? - (answer)It makes the molecule reactive for cyclization.
What enzyme closes the rings to form lanosterol? - (answer)Lanosterol synthase.
How many rings are formed in the lanosterol synthase cascade? - (answer)Four rings.
What is the immediate steroid product formed after cyclization of the squalene-derived precursor? -
(answer)Lanosterol.
How many steps are required to convert lanosterol to cholesterol according to the lecture? - (answer)19
steps.
How many carbons are lost when lanosterol becomes cholesterol? - (answer)3 carbons.
What enzyme class catalyzes the methyl-removal reactions during lanosterol to cholesterol conversion?
- (answer)Cytochrome P450 monooxygenases.
What enzyme adds acyl chains to cholesterol to form cholesteryl esters? - (answer)Lecithin-cholesterol
acyltransferase or LCAT.
