The Krebs cycle, also known as the citric acid cycle or TCA cycle, takes place in the mitochondria of cells. The main function of the Krebs cycle is to generate high-energy electron carriers in the form of NADH and FADH₂, and some ATP, which are then used in the electron transport chain to produce more ATP during cellular respiration. Here is a detailed step-by-step breakdown of the cycle's products after one glucose molecule goes through it:
1. Glycolysis: Before entering the Krebs cycle, one molecule of glucose (a 6-carbon molecule) is broken down into two molecules of pyruvate (each 3-carbon) via the process of glycolysis in the cytoplasm. Glycolysis produces a net gain of 2 ATP and 2 NADH.
2. Pyruvate Decarboxylation: Each pyruvate molecule is converted into acetyl-CoA (a 2-carbon molecule) by the pyruvate dehydrogenase complex in the mitochondrial matrix. This conversion produces 1 NADH and 1 CO₂ per pyruvate, totaling 2 NADH and 2 CO₂ per glucose molecule since each glucose splits into two pyruvates.
3. Krebs Cycle: Each acetyl-CoA then enters the Krebs cycle. Each turn of the cycle processes one acetyl-CoA and generates the following products:
- 3 NADH
- 1 FADH₂
- 1 ATP (or GTP)
- 2 CO₂
Since each glucose molecule produces two acetyl-CoA molecules, the Krebs cycle turns twice for each glucose molecule, resulting in doubled products:
- 6 NADH
- 2 FADH₂
- 2 ATP
- 4 CO₂
Therefore, after one glucose molecule has been completely processed through glycolysis, pyruvate decarboxylation, and the Krebs cycle, the products from just the Krebs cycle portion add up to:
- 6 NADH
- 2 ATP
- 4 CO₂
- 2 FADH₂
Thus, the correct option listing these products is:
6 NADH, 2 ATP, 4 CO₂, and 2 FADH₂
So, the correct choice is option 3.
