Q. 91 Detoxification of alcohol occurs in liver cells where peroxisomal enzymes remove hydrogen from it,
which is
(A) combined with water molecules to generate hydrogen peroxide.
(B) used to break down hydrogen peroxide.
(C) transferred to the mitochondria.
(D) transferred to oxygen molecules to generate hydrogen peroxide
Understanding Alcohol Detoxification in Liver Peroxisomes
Alcohol metabolism primarily occurs in the liver, where cells handle ethanol breakdown through multiple pathways. While much of this happens in the cytosol via alcohol dehydrogenase (ADH) and in mitochondria via acetaldehyde dehydrogenase (ALDH), peroxisomes play a key role in oxidizing longer-chain alcohols and certain ethanol derivatives. Peroxisomal enzymes, such as catalase and fatty acyl-CoA oxidases, initiate detoxification by removing hydrogen atoms from alcohol molecules.
This process generates hydrogen peroxide (H₂O₂) as a byproduct, which peroxisomes efficiently neutralize to prevent cellular damage. For students in biochemistry, molecular biology, or plant sciences (where similar peroxisomal functions aid in oxidative stress responses), grasping this mechanism is crucial for exams like NEET, CSIR NET, or research on xenobiotic metabolism.
The Key MCQ: Question 91 Breakdown
Question 91: Detoxification of alcohol occurs in liver cells where peroxisomal enzymes remove hydrogen from it, which is
(A) combined with water molecules to generate hydrogen peroxide.
(B) used to break down hydrogen peroxide.
(C) transferred to the mitochondria.
(D) transferred to oxygen molecules to generate hydrogen peroxide.
Correct Answer: (D)
Peroxisomal enzymes like catalase oxidize alcohol (ROH) in the presence of oxygen:
\ceROH+O2−>RCHO+H2O2
Here, hydrogen from alcohol transfers to oxygen molecules, forming hydrogen peroxide (H₂O₂). Catalase then decomposes H₂O₂:
\ce2H2O2−>2H2O+O2
This dual role makes peroxisomes efficient for alcohol detox, distinct from mitochondrial ethanol oxidation.
Detailed Explanation of All Options
-
(A) Combined with water molecules to generate hydrogen peroxide
Incorrect. Hydrogen from alcohol doesn’t react with water (H₂O) to form H₂O₂. Water lacks the oxidizing power; instead, oxygen accepts electrons/hydrogen. This option confuses hydration reactions with oxidation. -
(B) Used to break down hydrogen peroxide
Incorrect. The removed hydrogen produces H₂O₂ first, and catalase uses its own heme group—not the alcohol-derived hydrogen—to decompose H₂O₂ into water and oxygen. The hydrogen isn’t directly “used” for breakdown. -
(C) Transferred to the mitochondria
Incorrect. Peroxisomes handle their own oxidation independently. While metabolites like acetyl-CoA can shuttle to mitochondria via shuttles (e.g., malate-aspartate), hydrogen from peroxisomal alcohol oxidation stays local, forming H₂O₂ for catalase disposal. -
(D) Transferred to oxygen molecules to generate hydrogen peroxide
Correct. As explained, oxygen (O₂) acts as the electron acceptor: alcohol loses hydrogen (as hydride/protons), reducing O₂ to H₂O₂. This is a hallmark of peroxisomal β-oxidation and catalase-mediated detox.
Why Peroxisomes Matter in Liver Alcohol Metabolism
Peroxisomes contribute 10-20% to total ethanol oxidation in liver cells, especially under high alcohol loads. Unlike cytosolic ADH (producing acetaldehyde and NADH), peroxisomal catalase directly yields H₂O₂, linking to reactive oxygen species (ROS) management—relevant in oxidative stress studies. In research contexts, defects in peroxisomal disorders (e.g., Zellweger syndrome) impair this, leading to alcohol sensitivity.
For deeper dives, refer to textbooks like Lehninger Principles of Biochemistry or PubMed reviews on peroxisomal alcohol oxidation.
