Final answer:
Oxaloacetate is the compound central to the TCA cycle as it initiates and concludes the cycle by combining with acetyl-CoA to form citrate and being regenerated for the process to continue.
Step-by-step explanation:
The compound that plays a pivotal role in both the first and last steps of the tricarboxylic acid (TCA) cycle is oxaloacetate. This four-carbon molecule is crucial as it combines with acetyl-CoA in the first step to form citrate, and then it is regenerated in the last step to continue the cycle.
The continuous oxidation of acetyl-CoA to carbon dioxide and water, with the regeneration of oxaloacetate, underscores the central role oxaloacetate plays in the cycle, making it essential for the metabolism of carbohydrates, fats, and proteins. The TCA cycle, also known as the Krebs cycle or citric acid cycle, is a critical energy-harvesting pathway in cellular respiration where ATP, NADH, and FADH2 are produced.