Summary
Highlights
Glycolysis splits a 6-carbon glucose molecule into two 3-carbon pyruvic acid (pyruvate) molecules. This process doesn't require oxygen and yields a net gain of two ATPs and two NADHs. Glycolysis occurs in the cytoplasm of the cell.
The mitochondria, often called the power centers of the cell, are central to the next stages. Before entering the Krebs cycle, pyruvate undergoes oxidation. One carbon is cleaved off pyruvate, forming a 2-carbon acetyl-CoA molecule and reducing NAD+ to NADH. This happens twice for every glucose molecule.
The Krebs cycle begins when acetyl-CoA (a 2-carbon compound) merges with oxaloacetic acid (a 4-carbon molecule) to form citrate or citric acid (a 6-carbon molecule). This entire process is catalyzed by enzymes.
Citric acid is then oxidized through a series of steps. Carbons are cleaved off, forming CO2 (six CO2 molecules are produced for every glucose molecule). The cycle also generates NADHs, FADH2s, and ATP. These molecules are crucial as they are inputs for the electron transport chain, where the majority of ATP is produced.
From one glucose molecule: Glycolysis yields 2 net ATPs and 2 NADHs. Pyruvate oxidation (twice) yields 2 NADHs. The Krebs cycle (twice) yields 6 NADHs, 2 ATPs, and 2 FADH2s. In total, 4 direct ATPs, 10 NADHs, and 2 FADH2s are produced. These NADHs and FADH2s will generate an additional 34 ATPs in the electron transport chain, leading to a theoretical maximum of 38 ATPs per glucose molecule.
While glucose is the primary focus, the Krebs cycle is also the entry point for metabolizing proteins and fats. Proteins can be broken down into amino acids, and fats can be converted to glucose or directly into acetyl-CoA, allowing them to enter the Krebs cycle to generate ATP.
The video concludes by showing a more detailed diagram of the Krebs cycle, highlighting the pyruvic acid to acetyl-CoA conversion, the formation of citric acid, and the subsequent release of CO2, NADH, and FADH2 at various stages, confirming the overall summary of outputs.