Biotransformation and Xenobiotics

Question 1

Xenobiotic biotransformation is performed by multiple enzymes in multiple subcellular locations. Where would one of those enzymes most likely NOT be located?

a. cytosol
b. Golgi apparatus
c. lysosome
d. mitochondria
e. microsome

Answer 1

b. Golgi apparatus

Question 2

All of the following statements regarding hydrolysis, reduction and oxidation biotransformations are true EXCEPT:

a. The xenobiotic can be hydrolyzed
b. The xenobiotic can be reduced
c. There is a large increase in hydrophilicity
d. The reactions introduce a functional group to the molecule
e. The xenobiotic can be oxidized

Answer 2

c. There is a large increase in hydrophilicity

Question 3

Which of the following is often conjugated to xenobiotics during phase II biotransformation?

a. alcohol group
b. sulfhydryl group
c. sulfate group
d. aldehyde group
e. carbonyl group

Answer 3

c. sulfate group

Question 4

Which of the following is a true statement about the biotransformation of ethanol?

a. Alcohol dehydrogenase is only present in the liver
b. Ethanol is reduced to acetaldehyde by alcohol dehydrogenase
c. Ethanol and hydrogen peroxide combine to form acetaldehyde with the aid of catalase
d. In spite of its catalytic versatility, cytochrome P450 does not aid in ethanol oxidation
e. Acetaldehyde is oxidized to acetic acid in the mitochondria by aldehyde dehydrogenase

Answer 4

e. Acetaldehyde is oxidized to acetic acid in the mitochondria by aldehyde dehydrogenase

Question 5

Which of the following is responsible for the biotransformation and elimination of serotonin?

a. cytochrome P450
b. monoamine oxidase
c. flavin monooxygenase
d. xanthine oxidase
e. paraoxonase

Answer 5

b. monoamine oxidase

Question 6

which of the following reactions would likely NOT be catalyzed by cytochrome P450?

a. dehydrogenation
b. oxidative group transfer
c. epoxidation
d. reductive dehalogenation
e. ester cleavage

Answer 6

d. reductive dehalogenation

Question 7

All of the following statements regarding cytochrome P450 are true EXCEPT:

a. Poor metabolism or biotransformation of xenobiotics is often due to a genetic deficiency in cytochrome P450
b. Cytochrome P450 can be inhibited by both competitive and noncompetitive inhibitors.
c. Certain cytochrome P450 enzymes can be induced by one’s diet.
d. Increased activity of cytochrome P450 always slows the rate of xenobiotic activation
e. Induction of cytochrome P450 can lead to increased drug tolerance.

Answer 7

d. Increased activity of cytochrome P450 always slows the rate of xenobiotic activation

Question 8

Which of the following statements regarding phase II biotransformation (conjugation) reactions is true?

a. Phase II reactions greatly increase the hydrophilicity of the xenobiotic.
b. Phase II reactions are usually the rate-determining step in the biotransformation and excretion of xenobiotics.
c. Carboxyl groups are very common additions of phase II reactions.
d. Most phase II reactions occur spontaneously.
e. Increased phase II reactions rsult in increased xenobiotic storage in adipocytes.

Answer 8

a. Phase II reactions greatly increase the hydrophilicity of the xenobiotic.

Question 9

Where do most phase II biotransformations take place?

a. mitochondria
b ER (endoplasmic reticulum)
c. blood
d. nucleus
e. cytoplasm

Answer 9

e. cytoplasm

Question 10

Which of the following is not an important cosubstrate for phase II biotransformation reactions?

a. UDP-glucuronic acid
b. 3’-phosphoadenosine-5’-phosphosulfate (PAPS)
c. S-adenosylmethionine (SAM)
d. N-nitrosodiethylamine
e. acetyl CoA

Answer 10

d. N-nitrosodiethylamine