Cytochrome P450 Questions: Trivia Quiz!

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| By Clatkinson1
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Cytochrome P450 Questions: Trivia Quiz! - Quiz

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Questions and Answers
  • 1. 

    Which of the statements best describes the properties of the P450 enzymes?

    • A.

      Dimeric proteins, 40 - 50,000 MW; haem group with F2 in 2+ state

    • B.

      Multimeric proteins, 40 - 45,000 MW; protoporphyrin XI haem group

    • C.

      Monomeric proteins 40 - 50,000 MW; protoporhyrin IX haem prosthetic group

    Correct Answer
    C. Monomeric proteins 40 - 50,000 MW; protoporhyrin IX haem prosthetic group
    Explanation
    The P450 enzymes are monomeric proteins with a molecular weight of 40 - 50,000 MW. They contain a protoporhyrin IX haem prosthetic group.

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  • 2. 

    What are the main functions of P450?

    • A.

      Xenobiotic metabolism; steroid, fatty acid and vitamin reduction; steroid synthesis

    • B.

      Xenobiotic metabolism; steroid, fatty acid and vitamin oxidation; steroid biosynthesis

    • C.

      Xenobiotic metabolism; steroid, fatty acid and acetaldehyde oxidation; steroid biosynthesis

    Correct Answer
    B. Xenobiotic metabolism; steroid, fatty acid and vitamin oxidation; steroid biosynthesis
    Explanation
    The main functions of P450 include xenobiotic metabolism, which involves the breakdown and elimination of foreign substances in the body, such as drugs and toxins. P450 also plays a role in the oxidation of steroids, fatty acids, and vitamins, which is important for various physiological processes. Additionally, P450 is involved in the biosynthesis of steroids, which are essential for various functions in the body.

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  • 3. 

    What is the reaction scheme of P450?

    • A.

      DOH + NADPH + O2 --> DH + NADP + H20

    • B.

      DH + NADPH + O2 --> DOH + NADP + H2O

    • C.

      DH + NADP + H2O --> DOH + NADP + 02

    Correct Answer
    B. DH + NADPH + O2 --> DOH + NADP + H2O
    Explanation
    The correct answer is DH + NADPH + O2 --> DOH + NADP + H2O. This reaction scheme shows the conversion of DH (a substrate) into DOH (a product) in the presence of NADPH and O2. The reaction also produces NADP and H2O as byproducts.

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  • 4. 

    Which of these statements best describes the distribution of P450?

    • A.

      Highest levels in liver; lower levels in kidney and lung; some forms e.g. CYP1A1 only extrahepatic

    • B.

      Highest levels in liver; lower levels in kidney and intestine; some forms e.g. CYP3A1 only extrahepatic

    • C.

      Highest levels in liver; lower levels in gut and duodenum; some forms e.g. CYP1A2 only extrahepatic

    Correct Answer
    A. Highest levels in liver; lower levels in kidney and lung; some forms e.g. CYP1A1 only extrahepatic
  • 5. 

    Which of these statements best describes the properties of CYP2C9 substrates; and which are CYP2C9 substrates?

    • A.

      Areas of strong H-bond forming potential 5 - 7 A from site of metabollism; mainly NSAIDs but also warfarin and paracetamol

    • B.

      Areas of strong H-bond forming potential 5 - 7 A from site of metabolism; mainly CVS agents, also S-warfarin, paracetamol and aspirin

    • C.

      Areas of strong H bond/ion forming potential 5 - 10 A from site of metabolism; mainly NSAIDs, also S-warfarin, tolbutamide and ibuprofen

    Correct Answer
    C. Areas of strong H bond/ion forming potential 5 - 10 A from site of metabolism; mainly NSAIDs, also S-warfarin, tolbutamide and ibuprofen
    Explanation
    The correct answer states that CYP2C9 substrates have areas of strong H bond/ion forming potential 5 - 10 A from the site of metabolism. These substrates mainly include NSAIDs (nonsteroidal anti-inflammatory drugs) such as ibuprofen, as well as S-warfarin, tolbutamide, and paracetamol. This means that these drugs have the ability to form strong hydrogen bonds or ionic interactions within a specific distance from the site of metabolism, which is important for their interaction with the CYP2C9 enzyme.

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  • 6. 

    Which of these statements best describes the properties of CYP2D6 substrates; and which are CYP2D6 substrates?

    • A.

      Basic Nitrogen mainly ionised at physiological pH and a hydrophobic region, oxidation usually 5 - 7 A from basic N; mostly CVS and psychoactive agents e.g. propanolol, debrisoquine, amitriptyline, clozapine

    • B.

      Acidi Nitrogen mainly ionised at physiological pH and a hydrophilic region, oxidation usually 5 - 10 A from acidic Nitrogen; mostly CVS and psychoactive agents e.g. propranolol, desrioquine, amitriptyline, clozapine

    • C.

      Basic Nitrogen mainly ionised at physiological pH and a hydrophobic region, oxidation usually 5 - 7 A from basic N; mostly NSAIDs, also tolbutamide and S-warfarin

    Correct Answer
    A. Basic Nitrogen mainly ionised at physiological pH and a hydrophobic region, oxidation usually 5 - 7 A from basic N; mostly CVS and psychoactive agents e.g. propanolol, debrisoquine, amitriptyline, clozapine
    Explanation
    The correct answer describes the properties of CYP2D6 substrates as having a basic nitrogen that is mainly ionized at physiological pH and a hydrophobic region. These substrates undergo oxidation usually 5-7 A from the basic nitrogen. The examples given, such as propanolol, debrisoquine, amitriptyline, and clozapine, are mostly cardiovascular and psychoactive agents.

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  • 7. 

    Which of these statements best describes the properties of CYP3A4 substrates; and which are CYP3A4 substrates?

    • A.

      Large binding site allowing for considerable structural diversity in substrates, majority of binding involves ionic bonding; rifampicin, penicillin

    • B.

      Large binding site allowing for considerable structural diversity in substrates, majority of binding involving hydrophobic interactions; erythromycin, lidocaine, tamoxifen

    • C.

      Large binding site allowing for considerable structural diversity in substrates, majority of binding involves Hydrogen bonding; erythromycin, rifampicin

    Correct Answer
    B. Large binding site allowing for considerable structural diversity in substrates, majority of binding involving hydrophobic interactions; erythromycin, lidocaine, tamoxifen
    Explanation
    The correct answer states that CYP3A4 substrates have a large binding site that allows for a wide range of structural diversity in substrates. The majority of the binding between CYP3A4 and its substrates occurs through hydrophobic interactions. The specific substrates mentioned in the answer are erythromycin, lidocaine, and tamoxifen.

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  • 8. 

    Which P450 isoforms, in order, are resposible for imipramine metabolism?

    • A.

      CYP2D6, CYPA12, CYP3A4; CYP2C9

    • B.

      CYP2C19, CYP1A2, CYP3A4; CYP2D6

    • C.

      CYP2C9, CYPA12, CYP3A4; CYP2D6

    Correct Answer
    B. CYP2C19, CYP1A2, CYP3A4; CYP2D6
  • 9. 

    Which three factors contribute to determining metabolism by specific isoforms?

    • A.

      Topography of P450 active site; degree of steric hindrance of access to Fe-O complex; how easily substrate will react

    • B.

      Topography of substrate active site; degree of steric hindrance of access to P450 active site; ease of reaction

    • C.

      Topography of P450 active site; degree of steric hindrance of access to both Fe-O and P450 active site; ease of reaction

    Correct Answer
    A. Topography of P450 active site; degree of steric hindrance of access to Fe-O complex; how easily substrate will react
    Explanation
    The three factors that contribute to determining metabolism by specific isoforms are the topography of the P450 active site, the degree of steric hindrance of access to the Fe-O complex, and how easily the substrate will react. These factors affect the binding and accessibility of the substrate to the active site, as well as the ease with which the reaction can occur.

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  • 10. 

    How is the half life of diclofenac increased by P450 metabolism?

    • A.

      Fl atom moved from position 4 to 6 - preferential site of oxidation lost - shorter T1/2

    • B.

      Cl atom moved from position 6 to 4 - preferential site of reduction lost - longer T1/2

    • C.

      Cl atom moved from position 4 to 6 - preferential site of oxidation lost - longer T1/2

    Correct Answer
    C. Cl atom moved from position 4 to 6 - preferential site of oxidation lost - longer T1/2
    Explanation
    The movement of the Cl atom from position 4 to 6 in diclofenac leads to the loss of the preferential site of oxidation. This means that the drug is less susceptible to being metabolized by P450 enzymes, resulting in a longer half-life (T1/2). Therefore, the correct answer is that the Cl atom moved from position 4 to 6, leading to the loss of the preferential site of oxidation and a longer half-life.

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  • Mar 21, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • May 18, 2011
    Quiz Created by
    Clatkinson1
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