Question 1

Which of the following best describes the steroid nucleus found in all steroid hormones?

Accepted Answer

A planar, rigid structure composed of three six-membered rings and one five-membered ring, totaling 17 carbons.

Question 2

Which of the following is the rate-limiting, regulated step in cholesterol biosynthesis?

Accepted Answer

Conversion of HMG-CoA to mevalonate by HMG-CoA reductase

Question 3

A patient is prescribed a drug that inhibits HMG-CoA reductase. What is the expected effect on cholesterol synthesis?

Accepted Answer

Decreased conversion of HMG-CoA to mevalonate, leading to reduced cholesterol synthesis

Question 4

Which of the following hormones is synthesized from cholesterol and contains 21 carbons?

Accepted Answer

Cortisol

Question 5

Which enzyme catalyzes the conversion of cholesterol (C27) to pregnenolone (C21) in the mitochondria of the adrenal cortex and gonads?

Accepted Answer

Side Chain Cleavage Enzyme (CYP11A1)

Question 6

Which of the following best explains the effect of high intracellular cholesterol on HMG-CoA reductase?

Accepted Answer

It decreases gene expression and increases proteasomal degradation of HMG-CoA reductase.

Question 7

Which of the following statements about the regulation of HMG-CoA reductase is CORRECT?

Accepted Answer

AMP-activated protein kinase (AMPK) phosphorylates and inactivates HMG-CoA reductase.

Question 8

Which of the following is the correct sequence of intermediates in cholesterol synthesis starting from acetyl-CoA?

Accepted Answer

Acetyl-CoA $$\rightarrow$$ HMG-CoA $$\rightarrow$$ Mevalonate $$\rightarrow$$ Isopentenyl pyrophosphate $$\rightarrow$$ Farnesyl pyrophosphate $$\rightarrow$$ Squalene $$\rightarrow$$ Lanosterol $$\rightarrow$$ Cholesterol

Question 9

A patient with a genetic defect in 7-dehydrocholesterol reductase would most likely have impaired synthesis of which molecule?

Accepted Answer

Cholesterol

Question 10

Which of the following best describes the mechanism of action of steroid hormones?

Accepted Answer

They cross the cell membrane, bind intracellular receptors, and alter gene transcription.

Question 11

Which tissue is the primary site of cholesterol synthesis in the human body?

Accepted Answer

Liver

Question 12

Which of the following is TRUE regarding the activation of vitamin D3 (cholecalciferol) to its active form?

Accepted Answer

Cholecalciferol is first hydroxylated in the liver to 25-hydroxyvitamin D, then in the kidney to 1,25-dihydroxyvitamin D (calcitriol).

Question 13

Which of the following best explains why steroid hormones have slow onset but long duration of action?

Accepted Answer

They alter gene transcription, leading to changes in protein synthesis.

Question 14

Which of the following is a direct precursor to vitamin D3 (cholecalciferol) in the skin?

Accepted Answer

7-dehydrocholesterol

Question 15

Which of the following best describes the effect of insulin on HMG-CoA reductase activity?

Accepted Answer

Insulin stimulates dephosphorylation, activating HMG-CoA reductase.

Question 16

A patient with a deficiency in squalene monooxygenase would have impaired synthesis of which molecule?

Accepted Answer

Lanosterol

Question 17

Which of the following is a C19 steroid hormone synthesized in Leydig cells?

Accepted Answer

Testosterone

Question 18

Which of the following best describes the role of ACTH in cortisol synthesis?

Accepted Answer

ACTH stimulates cholesterol transport into mitochondria and increases steroidogenic enzyme expression.

Question 19

Which of the following is a key intermediate in cholesterol synthesis that also serves as a precursor for vitamin D synthesis in the skin?

Accepted Answer

7-dehydrocholesterol

Cholesterol, Steroid Hormones, and Calcitriol: Structure, Synthesis, and Regulation

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