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Mechanism Of Respiration
Respiration suggests that respiration is multi-step process in which glucose is oxidized during a series of reactions. These reactions can be subdivided into three stages:
Glycolysis
It is carried out by a group of soluble enzymes located in the cytosol (liquid part of cytoplasm). Chemically, the glucose undergoes a limited amount of oxidation to produce two molecules of pyruvate (a 3C compound), ATP and reduced nucleotide NADH.
The Tricarboxylic Cycle (TCA) or Krebs Cycle
The cycle brings about complete oxidation of pyruvate to CO2 and water. During the cycle about 10 reduced nucleotides (NADH) are generated. The TCA cycle operates in matrix of mitochondria when soluble enzymes for the cycle are present. This phase is also called oxidative decarboxylation since carbon atoms are oxidized to carbon dioxide during the phase.
The Electron Transport Chain (ETN)
It consists of a collection of electron carriers bound to the proteins of mitochondrial membranes. The system transfers electrons from NADH produced during glycolysis and TCA cycle, to oxygen. The electron transfers release a large amount of energy, much of which is stored in ATP produced from ADP and Pi.
Significance of Respiration
The process of respiration is significant in the following ways:
- It is essentially an energy providing mechanism. The stored energy of chemical compounds is converted into usable energy of ATP.
- Although most important aspect of respiratory pathway is to provide energy, but many important metabolic intermediates produced during glycolytic pathway and TCA cycle, are converted into important metabolites of cell. The metabolites derived from respiratory pathway include amino acids, pentose sugars used in cell wall and nucleotide synthesis. Precursors of porphyrins and acetyl CoA (coenzyme A) used in fatty acids, carbohydrates, gibberellins and abscisic acid synthesis.