Cellular Respiration Explained

Cellular Respiration

Cellular respiration is a process that is undergone in cells to break down molecules and produce ATP. The energy released from the broken down molecules are a result of spontaneous catabolic reactions. The most basic 3 metabolic stages within an animal cell are separated as followed: glycolysis, the Krebs Cycle, and the Electron Transport chain. Glycolysis and Krebs Cycle both synthesize ATP through substrate level phosphorylation which is ineffective through net ATP yield while the Electron Transport chain uses oxidative phosphorylation which has a highly effective ATP net yield.

The first step of cellular respiration in animal cells is anarobic, meaning it does not require oxygen.  This step of cellular respiration is glycolysis and in the end yields only a net gain of 2 ATP molecules.  Glycolysis occurs in the cytosol of the cell and is divided into two phases. The first phase is the investment phase in which 2 ATP is utilized though as series of catalyzed reactions to break down glucose into two glyceraldehydes phosphates. The two glyceraldehydes are then used in turn in the next phase of glycolysis: the pay-off phase. In the pay-off phase, another series of catalyzed reactions take place to produce 4 ATP and two pyruvate. In the end, the positive net gain of glycolysis is a mere 2 ATP. The pyruvate product of glycolysis is then sent to the Krebs Cycle if oxygen is present. If oxygen is not present, fermentation occurs.

Before the pyruvate can be used in the Krebs Cycle, the next step of cellular respiration (also anareobic), they need to be converted into Acetyl CoA. This process begins as the pyruvate leave the cytosol and enter the mitochondrial matrix through a transport protein. Soon after the pyruvate undergoes several oxidation reduction reactions they result in Acetyl CoA.