Question

Which of the following metabolites is not an intermediate in the triglyceride biosynthesis by Kennedy pathway?

• A. Lysophosphatidic acid
• B. Phosphatidic acid
• C. Diacylglycerol
• D. Glyceraldehyde-3-Phosphate

Hint:

The intermediates of the Kennedy pathway systematically build up to a triglyceride:
Glycerol-3-P $\rightarrow$ Lysophosphatidic acid $\rightarrow$ Phosphatidic acid $\rightarrow$ Diacylglycerol $\rightarrow$ Triacylglycerol.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The Kennedy pathway (glycerol-3-phosphate pathway) is the primary metabolic route responsible for the biosynthesis of triacylglycerols (triglycerides) and structural glycerophospholipids in cells.

Step 2: Detailed Explanation:
Let us trace the intermediates of the Kennedy pathway:
1. The pathway begins with the acylation of Glycerol-3-phosphate at the sn-1 position to yield Lysophosphatidic acid (1-acyl-glycerol-3-phosphate).
2. Lysophosphatidic acid is subsequently acylated at the sn-2 position to form Phosphatidic acid (1,2-diacylglycerol-3-phosphate).
3. Phosphatidic acid is dephosphorylated by the enzyme phosphatidic acid phosphatase to yield Diacylglycerol (DAG).
4. Finally, diacylglycerol is acylated at the C-3 position to produce Triacylglycerol (triglyceride).
Let us analyze Glyceraldehyde-3-phosphate:
Glyceraldehyde-3-phosphate is a three-carbon phosphorylated sugar that serves as an intermediate in glycolysis and the Calvin cycle.
Although it can be converted into dihydroxyacetone phosphate (DHAP) and then reduced to glycerol-3-phosphate, it is not a direct metabolic intermediate within the sequential steps of the Kennedy pathway itself.
Therefore, Glyceraldehyde-3-Phosphate is the correct answer.

Step 3: Final Answer:
Glyceraldehyde-3-Phosphate is not an intermediate in the Kennedy pathway.