What is the chemical reaction for cellular respiration

Cellular respiration is the process by which organisms convert the biochemical energy of nutrients into ATP. This process breaks down glucose into six carbon dioxide molecules and twelve water molecules. The overall chemical equation for aerobic respiration is C6H12O6 + 6O2 + 6H2O  →  12H2O + 6CO2 + 36/38ATP
and the chemical equations for anaerobic respiration are  C6H12O6 →  2C2H5OH + 2CO2 + 2ATP (for ethanol fermentation) and C6H12O6  →  2C3H6O3 + 2ATP (for lactic acid fermentation).

The cellular respiration is a catabolic process which breaks down large molecules into small molecules. The energy released during cellular respiration is used in the synthesis of ATP. Various sugars, amino acids, and fatty acids can be used as the substrate for cellular respiration.

Key Areas Covered

1. What is Cellular Respiration
     – Definition, Facts, types
2. What is the Chemical Equation for Cellular Respiration
     – Aerobic Respiration, Anaerobic Respiration

Key Terms: Aerobic Respiration, Anaerobic Respiration, ATP, Cellular Respiration, Glucose

Cellular respiration is a set of chemical reactions involved in the breakdown of nutrients into carbon dioxide and water, producing ATP. ATP is the main energy currency of the cell. Cellular respiration occurs within almost all organisms on the earth. Nutrients such as carbohydrates, proteins, and fatty acids are converted into glucose and used in the cellular respiration. There are two types of cellular respiration as aerobic respiration and anaerobic respiration. Final electron acceptor of aerobic respiration is molecular oxygen which is an inorganic compound in anaerobic respiration. The overall process of cellular respiration is shown in figure 1.

Figure 1: Cellular Respiration

What is the Chemical Equation for Cellular Respiration

The chemical equations for all types of cellular respiration are described below.

Aerobic Respiration

Aerobic respiration is the most efficient type of cellular respiration, which occurs in the presence of oxygen. The three steps of aerobic respiration are glycolysis, Krebs cycle, and electron transport chain.

1. Glycolysis

Glycolysis is the first step of aerobic respiration, which occurs in the cytoplasm. Two pyruvate molecules are produced from one glucose molecule during glycolysis. The chemical equation for glycolysis is,

Glucose + 2NAD+ 2Pi + 2ADP  →   2Pyruvate + 2NADH + 2ATP + 2H+ + 2H2O + Heat

These pyruvic acid molecules react with coenzyme-A to form acetyl-CoA.

Pyruvate + 2NAD+ + CoA   →  Acetyl CoA + NADH + CO2 + H+

2. Krebs Cycle

Acetyl CoA is completely broken down into carbon dioxide during Krebs cycle.

Acetyl CoA + 3NAD+ Q + GDP + Pi + 2H2O    →  CoA-SH + 3NADH + 3H+ +QH2 + GTP + 2CO2

3. Electron Transport Chain

Coenzymes made by the above two processes are reduced back by oxidative phosphorylation. The released energy is stored in ATP.

The overall chemical equation for aerobic respiration is shown below.

C6H12O6 + 6O2 + 6H2O  →  12H2O + 6CO2 + 36/38ATP

Anaerobic Respiration

Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen. The main type of anaerobic respiration is fermentation. Two types of fermentation can be identified: ethanol fermentation and lactic acid fermentation. The first steps of both fermentation methods are the glycolysis. The balanced chemical equations for both ethanol fermentation and lactic acid fermentation are shown below.

Ethanol Fermentation

 C6H12O6 →  2C2H5OH + 2CO2 + 2ATP

Lactic Acid Fermentation

C6H12O6  →  2C3H6O3 + 2ATP

Conclusion

During cellular respiration, one glucose molecule is broken down into six carbon dioxide molecules and twelve water molecules. The released energy is used in the production of ATP.

Reference:

1. “Steps of Cellular Respiration.” Khan Academy, Available here.

Image Courtesy:

1. “CellRespiration” By RegisFrey – Own work (CC BY-SA 3.0) via Commons Wikimedia