Lecture 15 - Cholesterol Metabolism

Question 1

__________ is the source of all carbons in synthesized cholesterol.

Answer 1

Acetyl-CoA

Question 2

___________ is 6 carbons and formed from 3 acetyl-CoA.

Answer 2

HMG-CoA

Question 3

What is the major regulated enzyme in the cholesterol biosynthetic pathway?

Answer 3

HMG-CoA reductase

Question 4

The activity of HMG-CoA reductase is increased by:

A. Thyroid hormone
B. Glucagon
C. Cortisol
D. All of these
E. None of these

Answer 4

A

Question 5

The activity of HMG-CoA reductase is decreased by:

A. Thyroid hormone
B. Insulin
C. Cortisol
D. All of these
E. None of these

Answer 5

C

Question 6

The synthesis of HMG-CoA reductase is repressed by:

A. Thyroid hormone
B. Glucagon
C. Cortisol
D. Cytosolic cholesterol
E. Insulin

Answer 6

D

Question 7

Which is NOT a product of the reaction that is catalyzed by HMG-CoA reductase?

A. Mevalonate
B. CoASH
C. HMG-CoA
D. NADP+

Answer 7

C - this is a reactant, which is combined with NADPH to yield mevalonate, CoASH, and 2 NADP+.

Question 8

Absorption and uptake of DIETARY cholesterol reaches the liver via what primary mechanism?

A. Chylomicron remnants
B. Extra hepatic de novo synthesis of cholesterol
C. Secretion of HDL from the liver
D. None of these
E. All of these

Answer 8

A

Question 9

Extrahepatic de novo synthesis of cholesterol reaches the liver via ____.

A. IDL
B. Chylomicron remnants
C. HDL
D. LDL receptors

Answer 9

C

Question 10

LDL binds to LDL-receptors on all cells via via what apoprotein?

Answer 10

Apo B-100

Question 11

A deficiency in apoliprotein B results in hypercholesterolemia. This means there is more cholesterol in the ________ because it can not get into tissues.

Answer 11

plasma

Question 12

What are 4 treatment options for hypercholesterolemia?

Answer 12

A. Statins
B. Cholestyramine
C. LIver transplant
D. LDL apheresis

Question 13

__________ is involved with intracellular storage of cholesterol as cholesterol esters.

A. ACAT
B. LCAT
C. MCAT

Answer 13

A

Question 14

__________ is involved with reverse transport of cholesterol, and associated with HDL.

A. ACAT
B. LCAT
C. MCAT
D. RCAT
E. HCAT

Answer 14

B

Question 15

________ converts cholesterol to bile acids, which are the main excretory form of cholesterol.

Answer 15

The liver

Question 16

How do statins work to treat hypercholesterolemia? (E.g. what do they inhibit?)

Answer 16

Statins inhibit HMG-CoA reductase,

a) limiting the synthesis of cholesterol from acetyl-CoA and
b) reducing back-up in the blood caused by lack of LDL receptors

Question 17

The carboxyl group on the side chain of the bile acids can form amide bonds with what two amino acids to form bile salts?

Answer 17

1. glycine

2. taurine

Question 18

Cholic acid and chenodeoxycholic acid are examples of:

Answer 18

major bile acids

Question 19

What are two features of bile acids and bile salts that allow them to be good emulsifiers?

Answer 19

1. Amphipathic (negative head group/neutral body)

2. Low pKa on side chain conjugated group

Question 20

___________ is the process of liver secretion and gut (small intestine reabsorption to the point where only about 5% of bile acids are excreted in the feces.

Answer 20

Enterohepatic circulation

Question 21

Bile acids are released into the lumen of the upper small intestine and then are reabsorbed by the lower small intestine into the portal circulation where they noncovalently bind __________.

Answer 21

albumin

Question 22

Which is activated by free cytosolic cholesterol?

A. HMG-CoA reductase
B. Synthesis of LDL receptors
C. ACAT
D. Synthesis and uptake of cholesterol

Answer 22

C - Free cytosolic cholesterol represses synthesis of HMG-CoA reductase and synthesis of LDL receptors, but ACTIVATES ACAT (meaning synthesis and uptake of cholesterol are reduced).