Final answer:
During fatty acid synthesis, acetoacetyl ACP is reduced, dehydrated, and further reduced to form a saturated acyl-S-ACP, extending the fatty acid chain, and this process repeats to eventually yield palmitoyl-ACP.
Step-by-step explanation:
In stage 3 of fatty acid synthesis, acetoacetyl ACP undergoes a series of reactions to be converted into a longer fatty acid chain. The process begins with the reduction of acetoacetyl-S-ACP to 3-hydroxyacyl-S-ACP by the enzyme 3-ketoacyl-ACP reductase, which uses NADPH as an electron donor
Then, 3-hydroxyacyl-S-ACP is dehydrated by 3-hydroxyacyl-ACP dehydratase to yield trans-∆²-enoyl-S-ACP. In the final reaction of this cycle, the enoyl-S-ACP is further reduced by enoyl-ACP reductase, again utilizing NADPH, to form a saturated acyl-S-ACP.
This process extends the fatty acid chain by two carbon atoms and is repeated until a 16-carbon palmitoyl-ACP is formed, at which point the fatty acid is released from ACP.
During stage 3 of fatty acid synthesis, acetoacetyl ACP is converted into acetoacetyl-S-ACP through condensation with malonyl-S-ACP. This condensation reaction is catalyzed by the enzyme 3-ketoacyl synthase.
The acetoacetyl-S-ACP is then further modified in subsequent reactions to form longer fatty acid chains