Which of the following is a characteristic of cholesterol?

Question

BlackTom AI · Accepted Answer

Cholesterol is a sterol synthesized in the liver and distributed in the body where it serves multiple biochemical roles, notably as a structural lipid in cell membranes and as the biochemical precursor for bile acids, steroid hormones, and vitamin D.

1. Relevant knowledge points and concepts
- Cholesterol is an animal-derived sterol; plants do not contain cholesterol in significant amounts.
- Dietary cholesterol and endogenous cholesterol are transported in lipoproteins (chylomicrons, VLDL/LDL/HDL), not freely dissolved in blood.
- In the liver, cholesterol is converted into bile acids (and bile salts) for fat digestion and absorption.
- In skin, the cholesterol derivative 7-dehydrocholesterol is converted by UV light to cholecalciferol (vitamin D3).

2. Step-by-step reasoning process
Step 1: Identify known functions of cholesterol — structural role and precursor roles.
Step 2: Recall metabolic pathways — hepatic conversion of cholesterol to bile acids; photochemical conversion of 7-dehydrocholesterol to vitamin D3 in the skin.
Step 3: Compare these established facts with each multiple-choice option to determine which matches cholesterol’s real functions.

3. Calculations
- None required for this conceptual question.

4. Why the correct answer is correct
The statement “it is a precursor for bile and vitamin D synthesis” is accurate. Cholesterol is enzymatically converted in the liver into bile acids, which are essential for emulsifying dietary fats. The skin contains 7-dehydrocholesterol (a cholesterol precursor) that is photolyzed by UVB to form vitamin D3, which is subsequently activated in the liver and kidney.

5. Why the other options are incorrect
- “Found in abundance in tropical fats such as palm oil”: incorrect because plant oils contain little to no cholesterol; cholesterol is abundant in animal fats.
- “It has no functions in the human body”: false; cholesterol has several critical functions as noted above.
- “It is absorbed directly into the blood”: incorrect; dietary cholesterol is packaged into chylomicrons and enters lymphatics before reaching the bloodstream and is transported in lipoproteins.

6. Conclusion
Therefore, the correct answer is “it is a precursor for bile and vitamin D synthesis,” which matches the provided answer.

Which of the following is a characteristic of cholesterol?单项选择题

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