Question 1

Which of the following statements best describes the structural features of cholesterol?

Accepted Answer

It is composed of four fused hydrocarbon rings (the steroid nucleus), a branched eight-carbon side chain at carbon 17, and a single hydroxyl group at carbon 3.

Question 2

Which enzyme catalyzes the rate-limiting step in cholesterol biosynthesis, and what is the product of this reaction?

Accepted Answer

HMG CoA reductase; produces mevalonate

Question 3

A patient is prescribed statins to lower their cholesterol. Statins act as competitive inhibitors of which enzyme, and what is the consequence for cholesterol synthesis?

Accepted Answer

HMG CoA reductase; decreased synthesis of mevalonate and cholesterol

Question 4

Which of the following mechanisms is NOT involved in the regulation of HMG CoA reductase activity?

Accepted Answer

Allosteric inhibition by ATP

Question 5

What is the primary fate of cholesterol in the body, considering it cannot be metabolized to CO$$_2$$ and water?

Accepted Answer

It is eliminated by conversion to bile acids and secretion into bile.

Question 6

Which of the following statements about bile acids and bile salts is correct?

Accepted Answer

Bile salts are conjugated forms of bile acids with glycine or taurine, making them fully ionized and more effective emulsifiers.

Question 7

A patient with cholelithiasis (gallstones) is unable to undergo surgery. Which treatment is used to gradually dissolve cholesterol gallstones, and what is its mechanism?

Accepted Answer

Oral administration of chenodeoxycholic acid, which increases bile acid concentration and solubilizes cholesterol.

Question 8

Which apolipoprotein is essential for the activation of lipoprotein lipase (LPL) and the hydrolysis of triglycerides in chylomicrons and VLDL?

Accepted Answer

Apo C-II

Question 9

Familial hypercholesterolemia (type IIa) is most commonly caused by which molecular defect?

Accepted Answer

Defective LDL receptor synthesis or function

Question 10

Which process describes the transfer of cholesteryl esters from HDL to VLDL in exchange for triglycerides, and which protein mediates this exchange?

Accepted Answer

Cholesteryl ester transfer; cholesteryl ester transfer protein (CETP)

Question 11

Which of the following best explains why plant sterols (phytosterols) can lower plasma cholesterol levels?

Accepted Answer

They compete with cholesterol for absorption in the intestine, reducing dietary cholesterol uptake.

Question 12

Which lipoprotein is primarily responsible for delivering cholesterol to peripheral tissues and is associated with increased risk of atherosclerosis when elevated?

Accepted Answer

Low-density lipoprotein (LDL)

Question 13

What is the function of lecithin:cholesterol acyltransferase (LCAT) in HDL metabolism?

Accepted Answer

It esterifies cholesterol using phosphatidylcholine, forming cholesteryl esters in HDL.

Question 14

A patient with a deficiency in the ABCAL transporter would most likely have impaired:

Accepted Answer

Efflux of cholesterol from peripheral cells to HDL

Question 15

Which of the following is the precursor for all classes of steroid hormones, and where does the rate-limiting step of steroid hormone synthesis occur?

Accepted Answer

Cholesterol; in the inner mitochondrial membrane by cholesterol side-chain cleavage enzyme (P450$$_{scc})$$

Question 16

Which hormone stimulates the synthesis and secretion of cortisol in the adrenal cortex during stress?

Accepted Answer

Adrenocorticotropic hormone (ACTH)

Question 17

Which of the following steps is required for the activation of the transcription factor SREBP-2, leading to increased expression of HMG CoA reductase?

Accepted Answer

Proteolytic cleavage of SREBP-2 in the Golgi when cholesterol is low

Question 18

Which of the following correctly describes the fate of LDL particles after receptor-mediated endocytosis in peripheral tissues?

Accepted Answer

LDL is degraded in lysosomes, releasing cholesterol, amino acids, and fatty acids.

Question 19

Which of the following is a distinguishing feature of lipoprotein(a) [Lp(a)] and its clinical significance?

Accepted Answer

It contains apolipoprotein(a) covalently linked to apo B-100 and is associated with increased risk of coronary heart disease.

Cholesterol, Lipoprotein, and Steroid Metabolism: Biochemistry Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard