Question

Which of the following are the principal precursors for milk fatty acid synthesis in the mammary gland?

• A. Acetate and beta-hydroxy butyrate
• B. Propionic acid and citric acid
• C. Cholesterol and Molonyl CoA
• D. Amino acids and citric acid

Hint:

In ruminants, rumen fermentation of fiber produces acetate and butyrate (which forms \(\beta\)-hydroxybutyrate).
These two molecules are the primary building blocks for milk fat synthesis in the mammary gland.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
In ruminants (like cows and buffaloes), milk fat consists primarily of triglycerides containing short-, medium-, and long-chain fatty acids.
Short- and medium-chain fatty acids (\( C_4 \) to \( C_{14} \)) are synthesized de novo within the mammary gland, while long-chain fatty acids are derived directly from dietary lipids or body fat reserves.

Step 2: Detailed Explanation:
Let us examine the biochemical precursors for de novo fatty acid synthesis in ruminant mammary glands:
In ruminants, carbohydrates are fermented in the rumen into volatile fatty acids (VFAs), primarily acetate, propionate, and butyrate.
- Acetate is absorbed into the bloodstream and acts as the major carbon source for de novo fatty acid synthesis in the mammary secretory cells.
- \(\beta\)-Hydroxybutyrate (derived from rumen butyrate) is also taken up by the mammary gland and serves as the primer molecule for initiating the fatty acid chain elongation process.
Together, acetate and \(\beta\)-hydroxybutyrate provide virtually all the carbon atoms needed for the synthesis of short- and medium-chain fatty acids in milk fat.
Propionate is primarily used by the liver for gluconeogenesis to make lactose, and does not serve as a direct precursor for fatty acids.
Therefore, acetate and \(\beta\)-hydroxybutyrate are the principal precursors.

Step 3: Final Answer:
The principal precursors for milk fatty acid synthesis in the mammary gland are Acetate and beta-hydroxy butyrate.