Detoxification Pathways Practice Questions

Q: The cytochrome involved in monooxygenase-mediated detoxification of drugs is:

Cyt P 450. ***Cyt P 450*** - **Cytochrome P450 (CYP450)** enzymes are a superfamily of heme-containing monooxygenases primarily responsible for the **metabolism of xenobiotics**, including the detoxification of drugs. - They catalyze oxidation reactions, introducing a hydroxyl group to substrates, which typically increases their **hydrophilicity** and facilitates excretion. *Cytochrome c* - **Cytochrome c** is a component of the **electron transport chain** in mitochondria, primarily involved in cellular respiration and energy production. - It acts as an **electron carrier** between Complex III and Complex IV, not directly in drug detoxification. *Cytochrome b5* - **Cytochrome b5** participates in various metabolic reactions, including **fatty acid desaturation** and cholesterol biosynthesis, and can sometimes assist CYP450 enzymes. - However, it does not function as a primary monooxygenase for drug detoxification itself. *Cytochrome oxidase* - **Cytochrome oxidase** (Complex IV) is the terminal enzyme in the **electron transport chain**, responsible for the reduction of oxygen to water. - Its main role is in cellular respiration, and it is not directly involved in drug monooxygenation or detoxification.

Q: What is the primary purpose of xenobiotic metabolism?

Increase water solubility. ***Increase water solubility*** - The primary goal of xenobiotic metabolism is to make these foreign compounds more **hydrophilic** (water-soluble). - This increased water solubility facilitates their **excretion** from the body via urine or bile. *Increase lipid solubility* - Increasing **lipid solubility** would make xenobiotics more likely to accumulate in **adipose tissue** and pass through cell membranes, hindering their excretion. - This is the opposite of the desired outcome for xenobiotic elimination. *Make them nonpolar* - Making xenobiotics **nonpolar** would be equivalent to increasing their lipid solubility, as nonpolar molecules tend to be lipid-soluble. - This would impede excretion and potentially lead to **bioaccumulation**, which is harmful. *None of the options* - This option is incorrect because xenobiotic metabolism specifically aims to increase **water solubility** for elimination.

Q: Which amino acid primarily conjugates with benzoic acid during its detoxification?

Glycine. ***Glycine*** - **Benzoic acid** is detoxified in the liver by conjugation with **glycine**, forming **hippuric acid**, which is then excreted in the urine. - This is a well-known Phase II detoxification reaction, enhancing the water solubility and elimination of the xenobiotic. *Alanine* - **Alanine** is involved in **gluconeogenesis** via the **glucose-alanine cycle** and protein synthesis. - It is not primarily involved in the conjugation of benzoic acid for detoxification. *Tyrosine* - **Tyrosine** is a precursor for **catecholamines**, thyroid hormones, and melanin. - It does not participate in the detoxification pathway of benzoic acid. *Leucine* - **Leucine** is a **branched-chain amino acid (BCAA)** essential for protein synthesis and muscle repair. - It has no known role in the conjugation or detoxification of benzoic acid.

Q: In the metabolism of xenobiotics, which of the following reactions does not occur in phase one?

Conjugation. ***Correct Answer: Conjugation*** - **Conjugation** reactions are characteristic of **Phase II metabolism**, NOT Phase I - In Phase II, a polar molecule (glucuronide, sulfate, acetyl, or glutathione) is added to the xenobiotic to increase water solubility and facilitate excretion - This process typically renders the xenobiotic inactive and more readily eliminated by the kidneys or bile - Common conjugation reactions include glucuronidation, sulfation, acetylation, and glutathione conjugation *Incorrect: Oxidation* - **Oxidation** is a primary **Phase I reaction**, primarily involving the cytochrome P450 (CYP450) enzyme system - Phase I oxidation introduces or exposes polar functional groups (-OH, -COOH, -NH2) - This makes the xenobiotic more reactive and prepares it for Phase II conjugation - Examples include hydroxylation, N-dealkylation, and O-dealkylation *Incorrect: Reduction* - **Reduction** reactions are also common in **Phase I metabolism** - Particularly important for compounds containing nitro groups, carbonyl groups, or azo compounds - These reactions can occur in various tissues, including the liver - Catalyzed by reductases such as cytochrome P450 reductase and other enzyme systems *Incorrect: Hydrolysis* - **Hydrolysis** is another key **Phase I reaction** that breaks down xenobiotics by adding water - Especially important for esters, amides, and other compounds with hydrolyzable bonds - Enzymes like esterases, amidases, and peptidases catalyze these reactions - Results in more polar metabolites that can undergo Phase II conjugation

Q: In liver, ethanol is converted to?

Acetaldehyde. ***Acetaldehyde*** - In the liver, **ethanol** is primarily metabolized by **alcohol dehydrogenase (ADH)** into **acetaldehyde**. - **Acetaldehyde** is a highly toxic compound responsible for many of the adverse effects associated with alcohol consumption. *Methanol* - **Methanol** is a different type of alcohol (wood alcohol) and is not a product of ethanol metabolism. - Methanol is metabolized to **formaldehyde** and then **formic acid**, which are highly toxic. *Lactate* - **Lactate** is a product of anaerobic glycolysis and is not directly formed from ethanol metabolism. - While heavy alcohol consumption can lead to **lactic acidosis**, lactate itself is not the immediate, direct conversion product of ethanol. *Citric acid* - **Citric acid** is a key intermediate in the **Krebs cycle (citric acid cycle)**, involved in aerobic respiration. - It is not a direct product of ethanol metabolism; rather, **acetyl-CoA** (derived from acetaldehyde metabolism) can enter the Krebs cycle.

Question 1

The cytochrome involved in monooxygenase-mediated detoxification of drugs is:

Accepted Answer

Cyt P 450

Answer

Cytochrome b5

Answer

Cytochrome c

Answer

Cytochrome oxidase

Question 2

What is the primary purpose of xenobiotic metabolism?

Accepted Answer

Increase water solubility

Answer

Increase lipid solubility

Answer

Make them nonpolar

Answer

None of the above

Question 3

Which amino acid primarily conjugates with benzoic acid during its detoxification?

Accepted Answer

Glycine

Answer

Alanine

Answer

Tyrosine

Answer

Leucine

Question 4

In the metabolism of xenobiotics, which of the following reactions does not occur in phase one?

Accepted Answer

Conjugation

Answer

Reduction

Answer

Hydrolysis

Answer

Oxidation

Question 5

In liver, ethanol is converted to?

Accepted Answer

Acetaldehyde

Answer

Methanol

Answer

Lactate

Answer

Citric acid

Detoxification Pathways — MCQs

Detoxification Pathways — MCQs

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