AIIMS Nagpur NO - 2018: Ketone bodies are synthesized from?

AIIMS Nagpur NO - 2018

Biochemistry & Nutrition

Easy

Appeared in: AIIMS Nagpur NO - 2018

Explanation

Ketone bodies are synthesized from acetyl-CoA in the liver mitochondria.
This process, called ketogenesis, is initiated when fatty acid oxidation produces an excess of acetyl-CoA.
Two acetyl-CoA molecules condense to form acetoacetyl-CoA, the first step in the pathway.
The primary ketone bodies are acetoacetate, 3-beta-hydroxybutyrate, and acetone.

Option B: Cholesterol is also synthesized from acetyl-CoA, but it is a separate metabolic pathway. It is a sterol used for cell membranes and hormone synthesis, not for ketogenesis.
Option C: Phospholipids are essential structural components of cell membranes and are not used as a primary fuel source for ketone body production.
Close distractor alert - Option D: Triglycerides are the storage form of fats. They are broken down into fatty acids, which are then oxidized to acetyl-CoA. Acetyl-CoA is the direct precursor, not triglycerides.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Biochemical pathway of ketogenesis as background academic context rather than a clinical decision trigger.
Understanding ketogenesis is crucial for managing diabetic ketoacidosis (DKA), a life-threatening complication of uncontrolled diabetes where excessive ketone body production leads to severe metabolic acidosis.
Ketogenic diets, which are high in fat and low in carbohydrates, intentionally induce a state of ketosis. These diets are used therapeutically for some forms of epilepsy, particularly in children, and are being investigated for other neurological conditions.
What if? If a patient has a carnitine deficiency, the transport of long-chain fatty acids into the mitochondria would be impaired. This would significantly reduce the rate of beta-oxidation and, consequently, decrease the production of both acetyl-CoA and ketone bodies, even during fasting.

How to Approach the Question

First, identify the core of the question: it asks for the direct building block or precursor for ketone bodies.
Recall the major metabolic pathways related to lipids and energy production.
Consider the context in which ketone bodies are made: fasting or low carbohydrate states. This triggers the breakdown of fats (triglycerides) into fatty acids.
Remember that fatty acids are broken down into two-carbon units of acetyl-CoA through beta-oxidation.
Recognize that this excess acetyl-CoA is the starting material for the synthesis (genesis) of ketone bodies.
Evaluate the options: Triglycerides are the source, but acetyl-CoA is the direct substrate. Cholesterol and phospholipids are involved in different lipid metabolic pathways.

Concept Tested & Keywords

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