What is the citric acid cycle and its significance?

The citric acid cycle (Krebs cycle, TCA cycle) is a central hub of aerobic metabolism occurring in the mitochondrial matrix. Acetyl-CoA (from carbohydrate, fat, or protein metabolism) combines with oxaloacetate to form citrate, which undergoes a series of reactions regenerating oxaloacetate. Per acetyl-CoA, the cycle produces 3 NADH, 1 FADH2, 1 GTP, and 2 CO2. The high-energy electron carriers (NADH, FADH2) feed into the electron transport chain for ATP generation. Beyond energy production, the cycle provides precursors for amino acid, nucleotide, and porphyrin biosynthesis, making it a metabolic hub.