Lipogenesis, or fatty acid synthesis, occurs in several cycles. A diagram of the

Question

Lipogenesis, or fatty acid synthesis, occurs in several cycles. A diagram of the reactions of the first cycle fatty acid synthesis is shown below. Which of the following statements are true? Select all the true statements. The reactions of lipogensis include, but are not limited to, two reductions are a dehydration. Each cycle lengthens the fatty acid chain by three carbon atoms. In lipognesis, acetyl molecules are activated by an acyl carrier protein (ACP) The first cycle of lipogensis yields CO_2, 1 NADP^+ and an acyl group attached to ACP. Malonyl-ACP adds a two-carbon group to the growing fatty acid chain with each cycled. Acetyl-SCoA provides the carbon used for fatty acid synthesis.

Explanation / Answer

1) The conversion of C=O to CHOH by NaDPH is a reduction. A second reduction occurs when the C=C bond is reduced to CH2 by NaDPH. The dehydration step is the loss of H2O from the alcohol to form C=C. Therefore, the 1st statement is correct.

2) A loss of CO2 occurs in the first step of the cycle. The final product contains 4 carbon atoms while the starting materials had 5 carbon atoms combined. The acetyl-ACP adds 2 carbon atoms from malonyl-ACP and hence there is a lengthening of chain by 2 carbon atoms. Therefore, the statement is false.

3) 2 moles of NaDP+ are released per first cycle as can be seen from the schematics. Therefore, the statement is false.

4) Malonyl-ACP provides 2 carbon atoms which adds to acetyl-ACP and hence the statement is true.

5) Acetyl-ACP is formed from acetyl-SCoA by transacylase enzyme and hence the statement is true.

Ans: Statements (1), (4) and (5) are true.

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