Question 1

A 5-year-old boy develops severe stomach pain after eating a big piece of fatty cheesecake.The serum amylase level is found to be mildly elevated.The plasma triglyceride level is 1200 mg/dL, and the total cholesterol level is 220 mg/dL.The parents mention that the child does not like fatty foods at all, but this was the first time he tasted cheesecake.Which apolipoprotein might be deficient in this patient to account for his fat intolerance?

A)A-I.
B)C-II.
C)B-100.
D)C-III.
E)E.

C-II.

Accepted Answer

The boy has type I hyperlipoproteinemia.Some cases are caused by a deficiency of apolipoprotein C-II, which is a required activator of lipoprotein lipase.Conditioned taste aversions are common in all metabolic diseases that lead to sickness after certain foods are eaten.

Question 2

Routine blood studies on an infant show turbid plasma with markedly elevated levels of triacylglycerol.A sample of plasma that has been left in the refrigerator overnight has cream-colored material floating on top.The underlying plasma is clear.Which type of hyperlipoproteinemia is most likely present in this infant?

A)Type I.
B)Type III.
C)Type IIb.
D)Type IIa.
E)Type IV.

Type I.

Accepted Answer

Chylomicrons, but not VLDL, rise to the surface on prolonged standing.

Question 3

On physical examination, you notice that a patient has tendon xanthomas.A blood analysis reveals a total cholesterol level of 350 mg/dL, which results mainly from raised levels of LDL, and normal levels of triglyceride.What other investigation would be helpful in this patient?

A)Look for eruptive xanthomas.
B)Perform a VLDL analysis.
C)Isolate the patient's lymphocytes and measure the number of LDL receptors.
D)Check for hyperthyroidism.
E)Measure fasting blood glucose.

Accepted Answer

This manifestation resembles familial hypercholesterolemia.In that case, you expect a reduction of functional LDL receptors to 50% of normal.

Question 4

Hypercholesterolemic patients taking 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) produce less cholesterol from endogenous synthesis.Lower intracellular cholesterol levels induce which of the following regulatory changes?

A)Enhanced VLDL formation in the liver.
B)Down-regulation of HMG-CoA reductase.
C)Higher lipoprotein lipase (LPL) activity.
D)Higher plasma chylomicron concentration.
E)An increased number of LDL receptors.

Accepted Answer

Cells acquire cholesterol according to their needs.If they cannot make it themselves, they have to get it from LDL.They do this by making more LDL receptors.

Question 5

A 33-year-old man is found to have tendon xanthomas.When questioned about his lifestyle, he says that he exercises regularly, eats balanced meals, and is not in any physical distress.A blood analysis reveals a plasma total cholesterol level of 350 mg/dL and a triglyceride level of 70 mg/dL.He is treated with cholestyramine and a statin and sent for further analysis.His hyperlipidemia is best classified as:

A)Type I.
B)Type V.
C)Type III.
D)Type IV.
E)Type IIa.

Accepted Answer

This manifestation resembles familial hypercholesterolemia.

Question 6

Cholestyramine can be used for the treatment of hypercholesterolemia, either alone or in combination with a statin.Which enzyme is most immediately affected by cholestyramine treatment?&#10;A)Cholesterol ester transfer protein.&#10;B)Acyl-CoA-cholesterol acyltransferase (ACAT).&#10;C)7-hydroxylase.&#10;D)HMG-CoA reductase.&#10;E)Lecithin-cholesterol acyl transferase (LCAT).

Accepted Answer

Cholestyramine is a nonabsorbed ion exchanger that binds bile acids in the small intestine, thus interrupting their enterohepatic circulation.7-Hydroxylase is disinhibited by the lack of bile acids and converts excess cholesterol to bile acids.

Question 7

You culture fibroblasts from a patient in the laboratory.In order to up-regulate the LDL receptors in these cells, you should:&#10;A)Add cholesterol esters to the medium.&#10;B)Add excess LDL to the medium.&#10;C)Inhibit HMG-CoA reductase.&#10;D)Inhibit the activity of acyl-CoA-cholesterol acyl transferase (ACAT).&#10;E)Add cholestyramine.

Accepted Answer

By inhibiting cholesterol synthesis, cellular free cholesterol is reduced, and LDL receptors are up-regulated.

Question 8

Excess cholesterol needs to be transported to the liver because it cannot be metabolized in most extrahepatic tissues.This "reverse" transport of cholesterol requires a lipoprotein that is not required for other routes of cholesterol transport.This lipoprotein is:

A)Intermediate-density lipoprotein (IDL).
B)Low-density lipoprotein (LDL).
C)High-density lipoprotein (HDL).
D)Very-low-density lipoprotein (VLDL).
E)Lipoprotein(a).

Accepted Answer

HDL picks up free cholesterol from cells.

Question 9

Statins are the most important type of cholesterol-lowering drug, and they lower specifically LDL rather than HDL cholesterol.How do the statins lower LDL cholesterol?&#10;A)By reducing the synthesis of apolipoprotein B-100, the major structural protein of VLDL and LDL.&#10;B)By stimulating the conversion of excess cholesterol to bile acids in the liver, thereby depleting cholesterol for LDL synthesis.&#10;C)By stimulating the transfer of cholesterol esters from VLDL and LDL to HDL.&#10;D)By inhibiting HMG-CoA reductase, thereby preventing cholesterol synthesis and forcing the cells to obtain their cholesterol from LDL.&#10;E)By stimulating the efflux of free cholesterol from cell membranes to HDL, thereby reducing the amount of cholesterol that is partitioned into LDL.

Accepted Answer

When the cells cannot make their own cholesterol, they have to obtain it from circulating LDL.To that end, they increase their synthesis of LDL receptors.

Deck 25: Lipid Transport