In which part of the mitochondrion does the Krebs cycle take place?

In which part of the mitochondrion does the Krebs cycle take place?

• A. In the cristae
• B. In the outer membrane
• C. In the matrix of the mitochondrion
• D. In the nucleus

Answer: (C)

The Krebs cycle occurs in the matrix of the mitochondrion. This semi-fluid space houses the enzymes that oxidize acetyl-CoA to CO2 and, in the process, generate NADH and FADH2 to carry electrons to the respiratory chain. After glycolysis, pyruvate enters the mitochondrion and is converted to acetyl-CoA in the matrix, which then combines with oxaloacetate to start the cycle. The electron carriers produced feed into the electron transport chain located on the inner membrane (the cristae), not in the matrix itself. The other locations aren’t correct for the cycle: the cristae are folds of the inner membrane where the electron transport chain sits, the outer membrane is simply a boundary, and the nucleus is a separate organelle containing DNA.

The Krebs cycle occurs in the matrix of the mitochondrion. This semi-fluid space houses the enzymes that oxidize acetyl-CoA to CO2 and, in the process, generate NADH and FADH2 to carry electrons to the respiratory chain. After glycolysis, pyruvate enters the mitochondrion and is converted to acetyl-CoA in the matrix, which then combines with oxaloacetate to start the cycle. The electron carriers produced feed into the electron transport chain located on the inner membrane (the cristae), not in the matrix itself. The other locations aren’t correct for the cycle: the cristae are folds of the inner membrane where the electron transport chain sits, the outer membrane is simply a boundary, and the nucleus is a separate organelle containing DNA.