Which metabolic pathway is initiated from acetyl coenzyme (Acetyl CoA)?

The metabolic pathway that is initiated from acetyl coenzyme A (Acetyl CoA) is the citric acid cycle. Acetyl CoA plays a crucial role in cellular metabolism, acting as a key substrate that enters the citric acid cycle, which is also known as the Krebs cycle or TCA (tricarboxylic acid) cycle.

Once Acetyl CoA enters this cycle, it combines with oxaloacetate to form citrate, which undergoes a series of reactions that produce energy in the form of ATP, as well as reducing equivalents in the form of NADH and FADH2. These products are essential for the production of energy via the electron transport chain, highlighting the importance of the citric acid cycle in aerobic metabolism.

The other metabolic pathways listed have distinct roles: glycolysis primarily involves the breakdown of glucose into pyruvate, while fatty acid synthesis focuses on the generation of fatty acids from acetyl CoA and other substrates. Protein metabolism involves the breakdown of amino acids, which does not directly initiate from acetyl CoA. Therefore, while these processes are interconnected, the specific initiation of the citric acid cycle from Acetyl CoA is what makes it the correct option.