Conversion of cholesterol into bile acids MCQs With Answer is a focused study resource for B.Pharm students covering bile acid synthesis, regulation, and clinical relevance. This introduction explores cholesterol to bile acids pathways, key enzymes like CYP7A1 and CYP27A1, conjugation by BAAT, and enterohepatic circulation involving ASBT, NTCP and BSEP. It highlights primary (cholic, chenodeoxycholic) and secondary (deoxycholic, lithocholic) bile acids, nuclear receptor regulation (FXR, LXR), and drug interactions such as bile acid sequestrants and ursodeoxycholic acid. Ideal for exam prep and pharmacology understanding, these MCQs emphasize mechanism, regulation, transport, and therapeutic implications of bile acid metabolism. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which enzyme catalyzes the rate-limiting step in the classical (neutral) pathway of bile acid synthesis from cholesterol?
- Cholesterol 7α-hydroxylase (CYP7A1)
- Sterol 27-hydroxylase (CYP27A1)
- 12α-hydroxylase (CYP8B1)
- Bile acid-CoA:amino acid N-acyltransferase (BAAT)
Correct Answer: Cholesterol 7α-hydroxylase (CYP7A1)
Q2. Conversion of cholesterol to 7α-hydroxycholesterol is primarily carried out in which cellular location?
- Mitochondrial matrix
- Smooth endoplasmic reticulum
- Peroxisome
- Golgi apparatus
Correct Answer: Smooth endoplasmic reticulum
Q3. Which enzyme determines the ratio of cholic acid to chenodeoxycholic acid by introducing 12α-hydroxylation?
- CYP7A1
- CYP8B1
- CYP27A1
- BAAT
Correct Answer: CYP8B1
Q4. The alternative (acidic) pathway of bile acid synthesis begins with oxidation at which position of cholesterol?
- 7α position by CYP7A1
- 27 position by CYP27A1
- 12α position by CYP8B1
- 3β position by 3β-HSD
Correct Answer: 27 position by CYP27A1
Q5. BAAT enzyme is responsible for which step in bile acid metabolism?
- 7α-hydroxylation of cholesterol
- Conjugation of bile acids with glycine or taurine
- 12α-hydroxylation to form cholic acid
- Dehydroxylation by intestinal bacteria
Correct Answer: Conjugation of bile acids with glycine or taurine
Q6. Which transporter mediates active ileal reuptake of bile acids during enterohepatic circulation?
- BSEP (ABCB11)
- NTCP (SLC10A1)
- ASBT (SLC10A2)
- OSTα/OSTβ
Correct Answer: ASBT (SLC10A2)
Q7. Hepatic uptake of conjugated bile acids from portal blood is mainly via which transporter?
- Bile salt export pump (BSEP)
- NTCP (SLC10A1)
- ASBT (SLC10A2)
- MRP2 (ABCC2)
Correct Answer: NTCP (SLC10A1)
Q8. Bile acids regulate their own synthesis mainly through activation of which nuclear receptor?
- Glucocorticoid receptor
- Farnesoid X receptor (FXR)
- Estrogen receptor
- Peroxisome proliferator-activated receptor (PPARα)
Correct Answer: Farnesoid X receptor (FXR)
Q9. Activation of FXR in ileal enterocytes induces secretion of which signaling molecule that inhibits hepatic CYP7A1?
- FGF19 (FGF15 in rodents)
- Insulin
- Glucagon
- Interleukin-6
Correct Answer: FGF19 (FGF15 in rodents)
Q10. Which bile acid is considered hepatotoxic and often sulfated by intestinal or hepatic enzymes to promote excretion?
- Cholic acid
- Chenodeoxycholic acid
- Lithocholic acid
- Glycocholic acid
Correct Answer: Lithocholic acid
Q11. Secondary bile acids are formed by bacterial action in the intestine by which primary reaction?
- 7α-dehydroxylation
- Conjugation with glycine
- Peroxisomal beta-oxidation
- 12α-hydroxylation
Correct Answer: 7α-dehydroxylation
Q12. Which of the following is a primary bile acid synthesized in the liver?
- Deoxycholic acid
- Lithocholic acid
- Cholic acid
- Ursodeoxycholic acid (in humans, secondary)
Correct Answer: Cholic acid
Q13. Conjugation of bile acids with taurine versus glycine affects their pKa and detergency; taurine conjugates are generally:
- Less water-soluble than glycine conjugates
- More acidic with lower pKa than glycine conjugates
- Incapable of forming micelles
- Not reabsorbed in the ileum
Correct Answer: More acidic with lower pKa than glycine conjugates
Q14. Bile salt export pump (BSEP/ABCB11) is responsible for which process?
- Uptake of bile acids into hepatocytes
- Secretion of bile salts into bile canaliculi
- Conjugation of bile acids with amino acids
- Reabsorption of bile salts in the ileum
Correct Answer: Secretion of bile salts into bile canaliculi
Q15. Which drug class binds bile acids in the gut, prevents reabsorption, and upregulates hepatic CYP7A1 leading to increased conversion of cholesterol into bile acids?
- Statins
- Bile acid sequestrants (e.g., cholestyramine)
- Fibrates
- ACE inhibitors
Correct Answer: Bile acid sequestrants (e.g., cholestyramine)
Q16. A deficiency of CYP27A1 enzyme causes which clinical condition related to bile acid metabolism?
- Gilbert’s syndrome
- Cerebrotendinous xanthomatosis
- Hemochromatosis
- Crigler-Najjar syndrome
Correct Answer: Cerebrotendinous xanthomatosis
Q17. Which hepatic nuclear receptor upregulates CYP7A1 transcription in response to oxysterols, linking cholesterol status to bile acid synthesis?
- Liver X receptor (LXR)
- Farnesoid X receptor (FXR)
- Pregnane X receptor (PXR)
- Vitamin D receptor (VDR)
Correct Answer: Liver X receptor (LXR)
Q18. Which peroxisomal process is essential for side-chain shortening of bile acid intermediates?
- β-oxidation
- Glycolysis
- Gamma-oxidation
- Urea cycle
Correct Answer: β-oxidation
Q19. Measurement of which plasma marker reflects hepatic bile acid synthesis activity and is used in research/clinical studies?
- 7α-hydroxy-4-cholesten-3-one (C4)
- Total cholesterol only
- Serum alkaline phosphatase
- Gamma-glutamyl transferase (GGT)
Correct Answer: 7α-hydroxy-4-cholesten-3-one (C4)
Q20. Which statement best describes enterohepatic circulation of bile acids?
- Bile acids synthesized in the intestine are excreted in urine
- Bile acids secreted into bile are mostly reabsorbed in ileum and returned to liver via portal vein
- Bile acids are synthesized in the kidney and transported to liver
- Bile acids diffuse passively across colonic epithelium and are excreted unchanged
Correct Answer: Bile acids secreted into bile are mostly reabsorbed in ileum and returned to liver via portal vein
Q21. Which transporter is primarily responsible for basolateral efflux of bile acids from enterocytes into portal blood?
- OSTα/OSTβ
- BSEP
- NTCP
- ASBT
Correct Answer: OSTα/OSTβ
Q22. Ursodeoxycholic acid (UDCA) is used therapeutically because it:
- Is highly hydrophobic and toxic to hepatocytes
- Increases bile acid pool toxicity
- Is hydrophilic and can protect cholangiocytes and facilitate bile flow
- Directly inhibits CYP7A1 enzyme
Correct Answer: Is hydrophilic and can protect cholangiocytes and facilitate bile flow
Q23. Lithocholic acid is mainly formed from which primary bile acid by bacterial action?
- Cholic acid
- Chenodeoxycholic acid
- Ursodeoxycholic acid
- Glycocholic acid
Correct Answer: Chenodeoxycholic acid
Q24. Which enzyme is responsible for activating bile acids to bile acid-CoA thioesters before conjugation?
- BACS (bile acid CoA synthetase)
- BAAT
- CYP7A1
- ASBT
Correct Answer: BACS (bile acid CoA synthetase)
Q25. What is the primary physiological role of bile salts in the intestine?
- Act as hormones regulating blood glucose
- Emulsify dietary lipids and facilitate micelle formation for fat absorption
- Inhibit pancreatic enzyme secretion
- Directly digest proteins
Correct Answer: Emulsify dietary lipids and facilitate micelle formation for fat absorption
Q26. Which of the following decreases expression of hepatic CYP7A1 and thus reduces bile acid synthesis?
- FXR activation and FGF19 signaling
- LXR activation by oxysterols
- High demand for cholesterol to bile acids following bile acid sequestrant therapy
- Thyroid hormone stimulation
Correct Answer: FXR activation and FGF19 signaling
Q27. In bile acid synthesis, 12α-hydroxylation is required to form which bile acid?
- Chenodeoxycholic acid
- Cholic acid
- Lithocholic acid
- Ursodeoxycholic acid
Correct Answer: Cholic acid
Q28. Which clinical effect results from prolonged treatment with bile acid sequestrants?
- Increased LDL cholesterol due to decreased hepatic LDL receptors
- Decreased LDL cholesterol due to increased hepatic LDL receptor expression
- Direct inhibition of HMG-CoA reductase
- Enhanced intestinal absorption of fat-soluble vitamins with no change in cholesterol
Correct Answer: Decreased LDL cholesterol due to increased hepatic LDL receptor expression
Q29. Which bacterial modification tends to make bile acids less soluble and more likely to form gallstones?
- Conjugation with glycine
- Sulfation
- Dehydroxylation producing deoxycholic acid
- Hydroxylation at 7α position
Correct Answer: Dehydroxylation producing deoxycholic acid
Q30. The enzyme that performs 7α-hydroxylation (CYP7A1) belongs to which enzyme family?
- UDP-glucuronosyltransferases
- Cytochrome P450 monooxygenases
- Transferases
- Dehydrogenases
Correct Answer: Cytochrome P450 monooxygenases
Q31. Which statement about bile acid pool size is true?
- It is unaffected by diet or intestinal reabsorption
- It is maintained by a balance between hepatic synthesis and intestinal loss in feces
- It increases dramatically during fasting only
- All bile acids are lost on first pass and must be synthesized de novo every meal
Correct Answer: It is maintained by a balance between hepatic synthesis and intestinal loss in feces
Q32. Which transporter defect is commonly implicated in progressive familial intrahepatic cholestasis type 2 (PFIC2) affecting bile acid secretion?
- NTCP (SLC10A1)
- BSEP (ABCB11)
- ASBT (SLC10A2)
- OSTα/OSTβ
Correct Answer: BSEP (ABCB11)
Q33. Bile acids act as signaling molecules; activation of intestinal FXR leads to which immediate effect relevant to bile acid homeostasis?
- Increase in CYP7A1 transcription in liver
- Secretion of FGF19 that represses hepatic bile acid synthesis
- Stimulation of pancreatic lipase secretion
- Upregulation of ASBT expression to prevent reabsorption
Correct Answer: Secretion of FGF19 that represses hepatic bile acid synthesis
Q34. Which laboratory change would you expect after administration of a bile acid sequestrant?
- Decreased hepatic CYP7A1 activity
- Increased fecal bile acid excretion and upregulated CYP7A1
- Decreased LDL receptor expression
- Increased enterohepatic recycling efficiency
Correct Answer: Increased fecal bile acid excretion and upregulated CYP7A1
Q35. Which bile acid is commonly measured as a hydrophobic, cytotoxic component increased in cholestasis?
- Ursodeoxycholic acid
- Glycocholic acid
- Chenodeoxycholic acid and lithocholic acid components
- Conjugated bilirubin
Correct Answer: Chenodeoxycholic acid and lithocholic acid components
Q36. Which process in the liver converts bile acid intermediates into mature C24 bile acids by shortening the side chain?
- Peroxisomal β-oxidation and thiolysis
- Mitochondrial TCA cycle
- Endoplasmic reticulum glycosylation
- Golgi-dependent sulfation
Correct Answer: Peroxisomal β-oxidation and thiolysis
Q37. Which of the following drugs induces hepatic CYP enzymes and can alter bile acid metabolism and enterohepatic cycling?
- Rifampicin (rifampin)
- Proton pump inhibitors
- Metformin
- Levothyroxine
Correct Answer: Rifampicin (rifampin)
Q38. Which clinical sign is directly attributable to impaired bile acid secretion into the intestine?
- Hyperglycemia
- Fat malabsorption and steatorrhea
- Polyuria
- Hypokalemia
Correct Answer: Fat malabsorption and steatorrhea
Q39. Which hepatic transporter mediates canalicular excretion of conjugated bilirubin and some bile salts when BSEP is impaired?
- MRP2 (ABCC2)
- NTCP (SLC10A1)
- ASBT (SLC10A2)
- OSTα/OSTβ
Correct Answer: MRP2 (ABCC2)
Q40. Which bile acid is formed by 7α-dehydroxylation of cholic acid by intestinal bacteria?
- Deoxycholic acid
- Chenodeoxycholic acid
- Glycochenodeoxycholic acid
- Ursodeoxycholic acid
Correct Answer: Deoxycholic acid
Q41. Which hormone or metabolic state tends to suppress CYP7A1 expression and decrease bile acid synthesis?
- Hypothyroidism
- Insulin resistance and high bile acid levels via FXR signaling
- Acute fasting with low insulin
- Activation of LXR by oxysterols
Correct Answer: Insulin resistance and high bile acid levels via FXR signaling
Q42. Taurocholic acid differs from glycocholic acid by which structural feature?
- Cholesterol backbone rather than steroid
- Taurine conjugation instead of glycine conjugation
- Additional hydroxylation at C7
- Shorter side chain length
Correct Answer: Taurine conjugation instead of glycine conjugation
Q43. Which of the following best explains why bile acids are effective detergents in the gut?
- They are strictly hydrophobic molecules that dissolve in lipids only
- They are amphipathic molecules with both hydrophobic and hydrophilic faces that form micelles
- They have strong enzymatic activity to hydrolyze triglycerides
- They precipitate dietary fats making them more absorbable
Correct Answer: They are amphipathic molecules with both hydrophobic and hydrophilic faces that form micelles
Q44. In cholestatic liver disease, accumulation of which bile acid species is most associated with hepatocellular injury?
- Hydrophilic ursodeoxycholic acid
- Hydrophobic bile acids such as chenodeoxycholic and lithocholic acids
- Conjugated bile acids exclusively
- Bile alcohols only
Correct Answer: Hydrophobic bile acids such as chenodeoxycholic and lithocholic acids
Q45. Which genetic or pharmacologic intervention would most likely increase fecal bile acid excretion?
- Overexpression of NTCP in liver
- Administration of an ASBT inhibitor
- Activation of BSEP canalicular transporter
- Inhibition of intestinal bacterial dehydroxylases
Correct Answer: Administration of an ASBT inhibitor
Q46. Which metabolic consequence follows prolonged reduction in bile acid pool due to ileal resection?
- Enhanced fat absorption
- Increased risk of fat-soluble vitamin deficiencies and steatorrhea
- Decreased hepatic cholesterol synthesis exclusively
- Reduced fecal cholesterol excretion
Correct Answer: Increased risk of fat-soluble vitamin deficiencies and steatorrhea
Q47. Which enzyme participates in the early step of bile acid synthesis by converting 7α-hydroxycholesterol into downstream oxidized intermediates in the acidic pathway?
- CYP7B1 (oxysterol 7α-hydroxylase)
- HMG-CoA reductase
- BAAT
- ASBT
Correct Answer: CYP7B1 (oxysterol 7α-hydroxylase)
Q48. Which drug used to dissolve cholesterol gallstones acts by reducing cholesterol saturation in bile and altering the bile acid pool?
- Colesevelam
- Ursodeoxycholic acid (UDCA)
- Rifampicin
- Metformin
Correct Answer: Ursodeoxycholic acid (UDCA)
Q49. Which pathway predominates in humans for total bile acid synthesis under normal conditions?
- Classical (neutral) CYP7A1-dependent pathway
- Alternative (acidic) CYP27A1-dependent pathway exclusively
- Peroxisomal-only pathway
- Bacterial synthesis in colon predominates
Correct Answer: Classical (neutral) CYP7A1-dependent pathway
Q50. Which clinical therapy targets ileal bile acid transport to lower LDL cholesterol by increasing bile acid excretion?
- HMG-CoA reductase inhibitors only
- ASBT inhibitors or bile acid sequestrants
- BSEP activators
- NTCP agonists
Correct Answer: ASBT inhibitors or bile acid sequestrants
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