Xenobiotic Definition & Metabolism (PDF)

1. Which of the following best defines a xenobiotic? A) A naturally occurring substance in the body B) A chemical substance that is foreign to an organism’s natural biological system C) A substance produced by the body D) A regular part of an organism’s diet Answer: B 2....

1. Which of the following best defines a xenobiotic? A) A naturally occurring substance in the body B) A chemical substance that is foreign to an organism’s natural biological system C) A substance produced by the body D) A regular part of an organism’s diet Answer: B 2. Which of the following is NOT a category of xenobiotics? A) Combustion/Air Pollutants B) Drugs and Cosmetics C) Vitamins and Minerals D) Industrial Waste Answer: C 3. Which of the following is an example of a xenobiotic? A) Glucose B) Insulin C) Antibiotics D) Water Answer: C 4. Which mode of human exposure to xenobiotics involves the absorption of pollutants through the skin? A) Inhalation B) Ingestion C) Skin Contact D) Injection Answer: C 5. What is the primary function of Phase 1 in xenobiotic metabolism? A) Absorption of xenobiotics into the body B) Excretion of xenobiotics C) Introduction of functional groups to xenobiotics D) Distribution of xenobiotics in the bloodstream Answer: C 6. Which of the following enzymes is most directly involved in Phase 1 of xenobiotic metabolism? A) Cytochrome P450 B) Glutathione S-transferase C) ATP synthase D) Amylase Answer: A 7. Which mechanism of absorption involves the movement of small hydrophilic molecules through membrane pores? A) Active Transport B) Facilitated Diffusion C) Filtration D) Phagocytosis Answer: C 8. The Blood-Brain Barrier (BBB) restricts the entry of which type of substances into the brain? A) Lipid-soluble, non-ionized substances B) Large, ionized substances C) Water-soluble substances D) Non-ionized, small molecules Answer: B 9. Which phase of xenobiotic metabolism involves the conjugation of xenobiotics with polar compounds? A) Phase 1 B) Phase 2 C) Phase 3 D) Phase 4 Answer: B 10. Which of the following factors does NOT significantly influence drug metabolism? A) Diet B) Age C) Body Mass Index (BMI)  D) Genetic Polymorphisms Answer: C 11. Which of the following is a potential consequence of xenobiotic binding to plasma proteins? A) Increased distribution in tissues B) Decreased half-life of the compound C) Restricted distribution and excretion D) Increased free concentration in plasma Answer: C 12. Which component increases the rigidity of cell membranes? A) Phospholipids B) Glycolipids C) Cholesterol D) Proteins Answer: C 13. Which type of diffusion requires a carrier protein but does not require energy? A) Passive Diffusion B) Active Transport C) Facilitated Diffusion D) Phagocytosis Answer: C 14. What is the main organ involved in xenobiotic metabolism? A) Kidney B) Liver C) Lungs D) Skin Answer: B 15. What type of transport mechanism is involved in the absorption of lead via calcium transport systems? A) Passive Diffusion B) Active Transport C) Filtration D) Facilitated Diffusion Answer: B 16. Which of the following pollutants are absorbed through food and water? A) Pesticides B) Carbon Monoxide C) Lead D) Asbestos Answer: A 17. Which enzyme provides the electrons required for oxidation in the Cytochrome P450 system? A) ATP synthase B) NADPH-Cytochrome P450 Reductase C) Cytochrome c oxidase D) Glutathione S-transferase Answer: B 18. The lipid solubility of a xenobiotic is most critical during which phase? A) Absorption B) Distribution C) Metabolism D) Excretion Answer: A 19. Which of the following processes involves engulfing large particles by the cell membrane? A) Pinocytosis B) Phagocytosis C) Passive Diffusion D) Filtration Answer: B 20. Which substance is a common example of a lipophilic xenobiotic? A) Water B) DDT  C) Glucose D) Sodium Chloride Answer: B 21. Which route is the most significant for the excretion of non-gaseous, non-volatile xenobiotics? A) Lungs B) Urine C) Sweat D) Bile Answer: B 22. Which of the following is a consequence of genetic polymorphisms in Cytochrome P450? A) Altered drug metabolism B) Uniform drug response across populations C) Increased drug toxicity for all individuals D) Reduced enzyme specificity Answer: A 23. What role does NADPH play in the Cytochrome P450 system? A) Acts as a substrate B) Provides reducing equivalents C) Acts as an oxidizing agent D) Facilitates transport across membranes Answer: B 24. Which of the following factors can alter the plasma protein binding of xenobiotics? A) Age B) Environmental temperature C) Cholesterol levels D) Light exposure Answer: A 1. What is bioactivation? a) The breakdown of xenobiotics into harmless metabolites b) The biotransformation of xenobiotics into more toxic metabolites c) The excretion of xenobiotics from the body d) The absorption of xenobiotics in the gastrointestinal tract Answer: b) The biotransformation of xenobiotics into more toxic metabolites 2. Which of the following is true about P450 enzymes? a) They do not contain heme groups. b) They are located exclusively in the mitochondria. c) They are involved in metabolizing drugs and chemicals. d) They are not involved in the metabolism of cholesterol. Answer: c) They are involved in metabolizing drugs and chemicals. 3. What is the heme in P450 enzymes? a) A protein-binding molecule b) An oxygen-binding molecule c) A porphyrin cofactor containing ferric iron (Fe3+) d) A chloride-binding molecule Answer: c) A porphyrin cofactor containing ferric iron (Fe3+) 4. Where are Phase 1 enzymes primarily located? a) Cytosol b) Endoplasmic Reticulum (ER) c) Nucleus d) Mitochondria Answer: b) Endoplasmic Reticulum (ER) 5. Which of the following best describes the naming system for Cytochrome P450 enzymes? a) Based on the enzyme’s function b) Based on the enzyme’s molecular weight c) Based on the genetic sequence d) Based on the substrate specificity Answer: c) Based on the genetic sequence 6. Which CYP enzyme is responsible for metabolizing cholesterol and bile acids?  a) CYP2E1 b) CYP3A4 c) CYP1A2 d) CYP7A1 Answer: d) CYP7A1 7. How many different P450 enzymes does the human genome encode? a) 25 b) 50 c) 57 d) 75 Answer: c) 57 8. Which of the following is a feature of competitive inhibition? a) Two drugs compete for the same enzyme’s active site b) The drug binds to a site other than the enzyme’s active site c) The enzyme becomes permanently inactive d) The drug induces the enzyme to work faster Answer: a) Two drugs compete for the same enzyme’s active site 9. What can cause an increased risk of drug-drug interactions? a) Overlapping substrate specificity of CYP enzymes b) Low CYP enzyme activity c) Non-competitive inhibition d) Mechanism-based inhibition Answer: a) Overlapping substrate specificity of CYP enzymes 10. Which CYP enzyme is primarily responsible for metabolizing fat-soluble vitamins? a) CYP1A2 b) CYP2C9 c) CYP2E1 d) CYP3A4 Answer: d) CYP3A4 11. What is the function of CYP enzymes in the mitochondria? a) Metabolizing drugs b) Hydroxylation processes c) Activating molecular oxygen d) Processing xenobiotics Answer: b) Hydroxylation processes 12. Which of the following enzymes is involved in the metabolism of aromatic amines? a) CYP1A1 b) NAT2 c) CYP2D6 d) CYP3A4 Answer: b) NAT2 13. In the context of personalized medicine, which category of metabolizers requires lower doses of drugs? a) Extensive metabolizers b) Poor metabolizers c) Ultra-rapid metabolizers d) Intermediate metabolizers Answer: b) Poor metabolizers 14. What is the role of NADPH in CYP hydroxylation? a) It provides energy for the reaction. b) It acts as a substrate for the enzyme. c) It inhibits the enzyme activity. d) It increases the rate of hydroxylation. Answer: a) It provides energy for the reaction. 15. What occurs during non-competitive inhibition? a) The drug competes directly for the enzyme’s active site. b) The drug binds to a different site, altering enzyme function. c) The enzyme is induced to produce more proteins. d) The drug is metabolized faster by the enzyme. Answer: b) The drug binds to a different site, altering enzyme function. 16. Which of the following is true about enzyme induction? a) It decreases the rate of drug metabolism. b) It reduces the production of enzyme proteins. c) It involves transcriptional activation. d) It only affects constitutive enzymes. Answer: c) It involves transcriptional activation. 17. Which of the following drugs can cause mechanism-based (suicide) inhibition of CYP enzymes? a) Quinidine b) Simvastatin c) SKF 525A d) Erythromycin Answer: c) SKF 525A 18. Which enzyme is primarily responsible for metabolizing warfarin? a) CYP2C9 b) CYP1A2 c) CYP3A4 d) CYP2D6 Answer: a) CYP2C9 19. What is a key characteristic of mechanism-based inhibition? a) Competitive interaction at the enzyme’s active site b) Non-competitive binding that does not involve the active site c) Formation of a reactive metabolite that damages the enzyme d) Inhibition through induction of more enzyme proteins Answer: c) Formation of a reactive metabolite that damages the enzyme 20. How does rifampin affect the metabolism of oral contraceptives? a) It induces CYP3A4, increasing the breakdown of contraceptives. b) It inhibits CYP2C19, reducing the effectiveness of contraceptives. c) It induces CYP2D6, leading to faster clearance of contraceptives. d) It inhibits CYP3A4, prolonging the effect of contraceptives. Answer: a) It induces CYP3A4, increasing the breakdown of contraceptives. 21. Which of the following is an example of genetic polymorphism affecting drug metabolism? a) Inhibition of CYP enzymes by carbon monoxide b) Slow acetylation due to NAT2 gene variations c) Competitive inhibition of drugs metabolized by the same enzyme d) Induction of CYP enzymes by environmental factors Answer: b) Slow acetylation due to NAT2 gene variations 22. What can happen if a slow acetylator is exposed to aromatic amines? a) Faster metabolism of the amines b) Reduced risk of bladder cancer c) Increased accumulation of harmful hydroxylamines d) Enhanced detoxification by NAT2 Answer: c) Increased accumulation of harmful hydroxylamines 23. Which of the following statements is true about CYP3A4? a) It metabolizes only fat-soluble vitamins. b) It is not involved in drug metabolism. c) It is the most abundant CYP enzyme in the liver. d) It does not undergo enzyme induction. Answer: c) It is the most abundant CYP enzyme in the liver. 24. What does the term “ultra-rapid metabolizer” refer to? a) An individual with reduced enzyme activity b) A person who metabolizes drugs at an increased rate c) Someone who requires lower doses of drugs d) An individual with no CYP enzyme activity Answer: b) A person who metabolizes drugs at an increased rate 25. Which of the following is a consequence of enzyme induction? a) Increased risk of drug toxicity b) Decreased rate of drug metabolism c) Faster metabolism of drugs leading to reduced effectiveness d) Increased drug concentration in the blood  Answer: c) Faster metabolism of drugs leading to reduced effectiveness 26. What does the term “lethal synthesis” refer to? a) A process where a xenobiotic is metabolized into a beneficial compound b) A process where a xenobiotic is metabolized into a toxic metabolite c) A process where a xenobiotic is excreted unchanged d) A process where a xenobiotic enhances enzyme activity Answer: b) A process where a xenobiotic 27. Which enzyme is responsible for the oxidative metabolism of ethanol? a) CYP1A1 b) CYP2C9 c) CYP2E1 d) CYP3A4 Answer: c) CYP2E1 28. Which of the following best describes the role of cytochrome b5 in CYP reactions? a) It directly binds the substrate for metabolism. b) It provides reducing equivalents for CYP reactions. c) It acts as a co-substrate for the enzyme reaction. d) It transports oxygen to the enzyme. Answer: b) It provides reducing equivalents for CYP reactions. 29. Which of the following CYP enzymes is highly inducible by smoking? a) CYP2E1 b) CYP1A2 c) CYP2C19 d) CYP3A4 Answer: b) CYP1A2 30. Which of the following best describes the effect of enzyme inhibitors? a) Increased metabolism of the drug b) Decreased plasma concentration of the drug c) Increased half-life of the drug d) Decreased drug efficacy Answer: c) Increased half-life of the drug 31. What is the main source of reducing equivalents in Cytochrome P450 reactions? a) NADPH b) FADH2 c) NADH d) ATP Answer: a) NADPH 32. Which CYP enzyme is involved in the metabolism of antipsychotic drugs? a) CYP2C19 b) CYP3A4 c) CYP2D6 d) CYP1A2 Answer: c) CYP2D6 33. What is the effect of grapefruit juice on CYP3A4? a) It induces CYP3A4, leading to increased metabolism of drugs. b) It inhibits CYP3A4, leading to decreased metabolism of drugs. c) It has no effect on CYP3A4. d) It increases the synthesis of CYP3A4 enzymes. Answer: b) It inhibits CYP3A4, leading to decreased metabolism of drugs. 34. Which of the following is a consequence of CYP enzyme inhibition? a) Faster clearance of the drug b) Increased drug plasma levels c) Enhanced drug metabolism d) Reduced risk of drug interactions Answer: b) Increased drug plasma levels 35. Which enzyme is predominantly involved in the metabolism of codeine to morphine? a) CYP3A4 b) CYP2E1  c) CYP2D6 d) CYP1A2 Answer: c) CYP2D6 36. Which of the following can be an effect of a poor metabolizer phenotype? a) Need for higher drug doses b) Increased risk of adverse drug reactions c) Rapid drug clearance d) Enhanced drug efficacy Answer: b) Increased risk of adverse drug reactions 37. Which of the following is a key role of CYP2C9? a) Hydroxylation of steroids b) Metabolism of nonsteroidal anti-inflammatory drugs (NSAIDs) c) Breakdown of glucose d) Metabolism of acetaminophen Answer: b) Metabolism of nonsteroidal anti-inflammatory drugs (NSAIDs) 38. Which of the following drugs is known to be a substrate for CYP2D6? a) Warfarin b) Metoprolol c) Acetaminophen d) Ibuprofen Answer: b) Metoprolol 39. Which of the following is a characteristic of a Phase II metabolic reaction? a) It involves oxidation of the drug. b) It usually results in more polar metabolites. c) It reduces drug efficacy. d) It occurs only in the liver. Answer: b) It usually results in more polar metabolites. 40. Which of the following describes the effect of a CYP enzyme inducer? a) Decreases the metabolism of other drugs b) Increases the synthesis of the CYP enzyme c) Reduces the plasma concentration of the CYP enzyme d) Enhances the therapeutic effect of other drugs Answer: b) Increases the synthesis of the CYP enzyme 41. What is the significance of polymorphism in CYP2D6? a) It leads to variability in the metabolism of drugs like antidepressants. b) It causes uniform drug metabolism across populations. c) It is only relevant for non-essential medications. d) It has no impact on drug metabolism. Answer: a) It leads to variability in the metabolism of drugs like antidepressants. 42. Which of the following is true about CYP3A4? a) It metabolizes only one specific drug. b) It is the least abundant CYP enzyme in the liver. c) It is involved in the metabolism of a wide range of drugs. d) It is not inducible by any external factors. Answer: c) It is involved in the metabolism of a wide range of drugs. 43. What is the effect of St. John’s Wort on drug metabolism? a) It inhibits CYP2C9. b) It induces CYP3A4, leading to decreased drug levels. c) It has no effect on CYP enzymes. d) It inhibits CYP3A4, leading to increased drug levels. Answer: b) It induces CYP3A4, leading to decreased drug levels. 44. Which enzyme is primarily responsible for the metabolism of paracetamol? a) CYP1A2 b) CYP2E1 c) CYP3A4 d) CYP2C19 Answer: b) CYP2E1 45. Which enzyme polymorphism is associated with the metabolism of isoniazid? a) CYP1A2  b) CYP2E1 c) NAT2 d) CYP2C19 Answer: c) NAT2 46. What is a possible outcome of CYP450 enzyme inhibition? a) Faster clearance of the drug from the body b) Reduced risk of adverse drug reactions c) Increased risk of drug toxicity d) Enhanced metabolism of the drug Answer: c) Increased risk of drug toxicity 47. Which of the following CYP enzymes is involved in the metabolism of antiepileptic drugs? a) CYP3A4 b) CYP2C19 c) CYP2D6 d) CYP1A2 Answer: b) CYP2C19 48. Which drug is a known inhibitor of CYP2C9? a) Fluconazole b) Rifampin c) Phenobarbital d) St. John’s Wort Answer: a) Fluconazole 49. Which of the following best describes the role of cytochrome P450 enzymes in drug metabolism? a) They are involved in the synthesis of proteins. b) They play a key role in the detoxification of drugs. c) They inhibit the action of drugs in the body. d) They increase the bioavailability of drugs. Answer: b) They play a key role in the detoxification of drugs. 50. Which of the following describes the process of enzyme induction? a) Decrease in enzyme synthesis b) Increase in enzyme synthesis leading to faster drug metabolism c) Inhibition of enzyme activity d) Inhibition of drug metabolism Answer: b) Increase in enzyme synthesis leading to faster drug metabolism