This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of lipid, Subject name: Biochemistry
In synthesis of fatty acid, energy is supplied by 
Select and explain. 
A. NAD, B. FAD, C. GTP, D. NADPH
D: NADPH
Answer: D: NADPH 
Explanation: An impoant point to remember is that the co-enzyme utilised for de novo synthesis is NADPH. The sources of NADPH for fatty acid synthesis are 1. Pentose Phosphate Pathway This is the main source. Tissues having active lipogenesis (liver, adipose tissue, lactating mammary gland) have an active HMP shunt pathway also. 2. Malic Enzyme Malate + NADP+ - Pyruvate + CO2 + NADPH + H+ The reaction also helps to transfer cytoplasmic oxaloacetate to the mitochondria. For every molecule of acetyl CoA delivered to the cytoplasm, one molecule of NADPH is formed and reducing equivalents are generated in cytoplasRef: DM Vasudevan - Textbook of Biochemistry, 6th edition, page no: 139