Krebs cycle location?

• A. Cytosol
• B. Nucleus
• C. Mitochondrial matrix
• D. Endoplasmic reticulum

Answer: (D)

Krebs cycle happens in the mitochondrial matrix. The enzymes that drive the cycle—such as citrate synthase, aconitase, isocitrate dehydrogenase, and others—are located in this fluid-filled compartment inside the mitochondrion. Acetyl-CoA enters the cycle by combining with oxaloacetate to form citrate right there in the matrix, and the cycle produces NADH and FADH2 that feed electrons into the electron transport chain on the inner mitochondrial membrane. The cytosol is where glycolysis occurs, the nucleus houses genetic material, and the endoplasmic reticulum handles protein and lipid synthesis, so they’re not the sites of the TCA cycle.