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 (acetoacetate, β-hydroxybutyrate, and acetone) are synthesized in the liver mitochondria.
The direct precursor and building block for this process, known as ketogenesis, is Acetyl CoA.
This pathway becomes active when fatty acid oxidation is high, leading to an abundance of Acetyl CoA that exceeds the capacity of the citric acid cycle.
The first step of ketogenesis involves the condensation of two molecules of Acetyl CoA to form acetoacetyl CoA.

Option B: Cholesterol is a steroid, not a precursor for ketone bodies. Although its synthesis also starts with Acetyl CoA, it follows a completely different and complex metabolic pathway.
Option C: Phospholipids are major structural components of cell membranes and are involved in cell signaling. They are not used as a primary substrate for ketone body synthesis.
Option D: Triglycerides are an indirect source. They are first broken down (lipolysis) into fatty acids and glycerol. The fatty acids then undergo beta-oxidation to produce Acetyl CoA. The question asks for the direct molecule from which ketone bodies are synthesized.

Visual 1: Flowchart - A diagram illustrating the pathway of ketogenesis, starting from the breakdown of fatty acids to Acetyl CoA, followed by the condensation steps to form acetoacetate, β-hydroxybutyrate, and acetone. This visualizes the central role of Acetyl CoA.
Visual 2: Diagram - A metabolic map showing the divergence of Acetyl CoA into two pathways: the Citric Acid Cycle (for energy) and Ketogenesis (when glucose is low). This helps explain why ketogenesis occurs.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Biochemical pathway of ketone body synthesis (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.
Nurses monitor for ketonuria (ketones in urine) and a fruity breath odor (from acetone) as key signs of DKA or severe starvation.
The principle of ketogenesis is therapeutically utilized in ketogenic diets, which are high-fat, low-carbohydrate diets used to manage refractory epilepsy in children and for weight loss.

How to Approach the Question

First, identify the core concept of the question, which is the biochemical synthesis of a specific group of molecules (ketone bodies).
Recall the major metabolic pathways related to lipids and carbohydrates. The question links fat metabolism (ketone bodies) to a precursor molecule.
Consider each option as a potential starting material. Think about the sequence of metabolic events.
Differentiate between direct and indirect precursors. Triglycerides are broken down into fatty acids, which are then broken down into Acetyl CoA. Acetyl CoA is the direct starting block for building ketone bodies.
Eliminate options that belong to entirely different metabolic pathways, such as cholesterol (steroid synthesis) and phospholipids (membrane structure).
Select the option that serves as the immediate substrate for the synthesis pathway in question.

Concept Tested & Keywords

QI7cUtpzbLudllZXNi0CJF

E6 Biochemistry U Satyanarayana 7th Edition — Part 1 (pp 26-420 of 840) p. 420-820