Biochemistry 4th Edition by Reginald Garrett, Charles Grisham

Exercise 15

Understanding how cells provide acetate units for fatty acid synthesis in the cytosol
In most cells, fatty acids are synthesized from acetate units in the cytosol. However, the primary source of acetate units is the TCA cycle in mitochondria, and acetate cannot be transported directly from the mitochondria to the cytosol. Cells solve this problem by exporting citrate from the mitochondria and then converting citrate to acetate and oxaloacetate. Then, because cells cannot transport oxaloacetate into mitochondria directly, they must convert it to malate or pyruvate, both of which can be taken up by mitochondria. Draw a complete pathway for citrate export, conversion of citrate to malate and pyruvate, and import of malate and pyruvate by mitochondria.
a. Which of the reactions in this cycle might require energy input
b. What would be the most likely source of this energy
c. Do you recognize any of the enzyme reactions in this cycle
d. What coenzymes might be required to run this cycle