What molecule enters the Krebs cycle?

The Krebs cycle, also known as the citric acid cycle, begins when acetyl-CoA enters the cycle and combines with oxaloacetate to form citrate. Acetyl-CoA is produced from pyruvate, which is generated from glucose during glycolysis. It serves as a critical entry molecule that carries the two-carbon acetyl group necessary for the cycle to progress. Throughout the Krebs cycle, the acetyl group undergoes oxidation and contributes to the production of energy-rich molecules, including NADH and FADH2, which are essential for the electron transport chain and ATP synthesis.

Glucose, while the initial substrate for cellular respiration, is metabolized during glycolysis to produce pyruvate, but it does not directly enter the Krebs cycle. NADH is one of the products of the Krebs cycle, formed during various enzymatic reactions within the cycle, but it does not serve as an entry molecule.