Cellular Respiration

Cellular Respiration

Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into ATP, and then release waste products. The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy in the process.

Overview

Cellular respiration is a crucial process for the survival of most organisms, as it provides the energy required for various cellular activities. It can be divided into three main stages: glycolysis, the citric acid cycle (also known as the Krebs cycle), and the electron transport chain.

Glycolysis

Main article: Glycolysis

Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. It occurs in the cytoplasm of the cell and does not require oxygen, making it an anaerobic process. During glycolysis, one molecule of glucose is converted into two molecules of pyruvate, with a net gain of two molecules of ATP and two molecules of NADH.

Citric Acid Cycle

Main article: Citric acid cycle

The citric acid cycle, also known as the Krebs cycle, takes place in the mitochondria of eukaryotic cells. It is an aerobic process, meaning it requires oxygen. The pyruvate produced in glycolysis is transported into the mitochondria, where it is converted into acetyl-CoA. This acetyl-CoA enters the citric acid cycle, where it undergoes a series of enzymatic reactions that produce ATP, NADH, and FADH2.

Electron Transport Chain

Main article: Electron transport chain

The electron transport chain is the final stage of cellular respiration and occurs in the inner mitochondrial membrane. It involves a series of protein complexes that transfer electrons from NADH and FADH2 to oxygen, the final electron acceptor. This process creates a proton gradient across the membrane, which drives the synthesis of ATP through oxidative phosphorylation.

Anaerobic Respiration

In the absence of oxygen, cells can undergo anaerobic respiration or fermentation. This process allows for the regeneration of NAD+ from NADH, enabling glycolysis to continue producing ATP. Common types of fermentation include lactic acid fermentation and alcoholic fermentation.

Importance

Cellular respiration is essential for the production of ATP, which is the primary energy currency of the cell. It powers various cellular processes, including muscle contraction, nerve impulse propagation, and biosynthesis.

See Also

• Photosynthesis
• Metabolism
• ATP synthase

References

• Berg, J. M., Tymoczko, J. L., & Stryer, L. (2002). Biochemistry. W.H. Freeman.
• Nelson, D. L., & Cox, M. M. (2008). Lehninger Principles of Biochemistry. W.H. Freeman.