Final answer:
The B vitamin essential for the TCA cycle to replenish oxaloacetate is pantothenic acid (vitamin B5), which is critical for producing coenzyme A; a key player in energy metabolism and synthesis of fatty acids and cholesterol.
Step-by-step explanation:
The B vitamin that is needed in very small amounts in the diet but whose role as a coenzyme in the TCA cycle is critical in helping to replenish oxaloacetate is pantothenic acid (vitamin B5). Pantothenic acid is a precursor to coenzyme A (CoA), which picks up acetyl groups to form acetyl CoA. Acetyl CoA then enters the TCA cycle, where it combines with oxaloacetate to form citrate, initiating the cycle that ultimately regenerates oxaloacetate. This continuous regeneration is vital for the cycle to proceed smoothly and for the metabolism of carbohydrates, fats, and proteins.
Functions of pantothenic acid include its involvement in the growth of infants and children, and the requirement of Coenzyme-A for the activation of acetate to acetyl-CoA, as well as for the synthesis of fatty acids and cholesterol. This illustrates the significance of this vitamin in maintaining essential metabolic processes.