Which of the following statements about β-oxidation of fatty acids is incorrect?

INI-CET EXAM -2025

Biochemistry & Nutrition

Medium

Appeared in: INI-CET EXAM -2025

Explanation

The statement is incorrect because ATP is not directly consumed during the transport of the fatty acyl group across the mitochondrial membrane via the carnitine shuttle.
ATP is required for the initial activation of the fatty acid into fatty acyl-CoA in the cytosol, a step that must occur before transport can begin.
The energy for the transport itself is not derived from ATP hydrolysis but from the concentration gradients and exchange mechanism of the carnitine-acylcarnitine translocase.
The thiokinase reaction that activates the fatty acid is the only step in this overall process that requires ATP.

Option A: This statement is correct. CAT I (on the outer membrane) and CAT II (on the inner membrane) are both essential enzymes in the carnitine shuttle system that facilitates the transport of fatty acids across both mitochondrial membranes into the matrix.
Option C: This statement is correct. The enzyme CAT I, located on the outer mitochondrial membrane, catalyzes the reaction: Fatty Acyl-CoA + Carnitine → Acyl-carnitine + CoA. This reaction occurs on the cytosolic side, releasing CoA into the cytosol.
Option D: This statement is correct. The enzyme CAT II, located on the inner mitochondrial membrane, catalyzes the reaction inside the matrix: Acyl-carnitine + CoA → Fatty Acyl-CoA + Carnitine. This releases free carnitine into the mitochondrial matrix, which is then shuttled back to the cytosol.

Visual 1: Diagram: The Carnitine Shuttle. A visual showing the outer and inner mitochondrial membranes, with enzymes CAT I and CAT II, the translocase, and the movement of fatty acyl-CoA, carnitine, and acyl-carnitine between the cytosol and the mitochondrial matrix. This would clearly illustrate where each reaction occurs and which molecules are involved.
Visual 2: Flowchart: Steps of Fatty Acid Transport and Activation. A flowchart starting with a fatty acid in the cytosol, showing the ATP-dependent activation step, followed by the sequential steps of the carnitine shuttle, and ending with fatty acyl-CoA inside the matrix, ready for β-oxidation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The question tests the understanding of the biochemical pathway for transporting fatty acids into the mitochondria for β-oxidation, specifically the roles of ATP, carnitine, and associated enzymes as background academic context rather than a clinical decision trigger.
Carnitine deficiency, either genetic (e.g., CPT-I or CPT-II deficiency) or acquired (e.g., in preterm infants, liver disease), impairs the ability to use long-chain fatty acids for energy.
This leads to hypoglycemia (as the body becomes overly reliant on glucose), muscle weakness, and accumulation of lipids in tissues.
What if? If a patient has a CPT-II deficiency, they would be able to activate fatty acids and transport them to the intermembrane space, but not into the matrix. This would lead to an accumulation of acyl-carnitines and muscle weakness, especially during fasting or exercise when fatty acid oxidation is crucial.

How to Approach the Question

First, identify the core concept: the question asks for an incorrect statement about the transport of fatty acids for β-oxidation.
Break down the process mentally into key stages: 1. Activation in the cytosol, 2. Transport across the mitochondrial membranes (the carnitine shuttle).
Evaluate each option against the known steps of this pathway.
Option A: Recall the roles of CAT I and CAT II. Both are part of the transport system. This seems correct.
Option B: Consider the energy requirements. Remember that ATP is used for activation (fatty acid → fatty acyl-CoA), which happens before the transport shuttle. The shuttle itself is an exchange, not an ATP-driven pump. This makes the statement that ATP is required for transport questionable.
Option C: Trace the path of CoA. It's used for activation, then released by CAT I in the cytosol. This seems correct.

Concept Tested & Keywords

Concept Tested: The question tests the understanding of the biochemical pathway for transporting fatty acids into the mitochondria for β-oxidation, specifically the roles of ATP, carnitine, and associated enzymes.
Stem keywords: β-oxidation, fatty acids, incorrect statement
Lead-in keywords: Which of the following statements, is incorrect
Negative lead-in flag: is incorrect

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