The overall chemical equation for cellular respiration can be summarized as follows:
C6H12O6 (glucose) + 6O2 (oxygen) -> 6CO2 (carbon dioxide) + 6H2O (water) + energy (as ATP)
In this equation, glucose, a six-carbon sugar molecule, is broken down in the presence of oxygen through a series of enzyme-catalyzed reactions. During this process, the bonds within glucose are rearranged, and the released energy is used to synthesize ATP molecules.
The cellular respiration process can be further divided into three main stages: glycolysis, the Krebs cycle (also known as the citric acid cycle), and oxidative phosphorylation.
1. Glycolysis:
- Occurs in the cytoplasm.
- Glucose is broken down into two molecules of pyruvate (a three-carbon molecule).
- 2 ATP molecules are used, and 4 ATP molecules are gained (net gain of 2 ATP).
- 2 NADH molecules are produced.
2. Krebs Cycle:
- Occurs in the mitochondria.
- Each pyruvate molecule from glycolysis is further broken down and combined with coenzyme A to form Acetyl CoA.
- Over multiple reactions, Acetyl CoA is oxidized to release CO2 and produce ATP, NADH, and FADH2 molecules.
3. Oxidative Phosphorylation:
- Also occurs in the mitochondria.
- NADH and FADH2 molecules produced in glycolysis and the Krebs cycle pass their electrons to the electron transport chain, creating an electrochemical gradient across the mitochondrial membrane.
- The flow of protons through ATP synthase enzyme uses this gradient to produce ATP molecules through a process called chemiosmosis.
Ultimately, cellular respiration converts the chemical energy stored in glucose into the usable energy currency of the cell, ATP. The ATP produced is then utilized by cells to perform various functions, including muscle contraction, nerve impulse transmission, chemical synthesis, and active transport of molecules across membranes.
