Cellular respiration is necessary to transform glucose into energy. The ATP created via chemical processes then powers cellular reactions. Aerobic respiration only occurs when glucose burns to release energy in the presence of oxygen (Russell et al., 2016). Three essential stages ensure proper aerobic respiration: glycolysis, Krebs’ cycle, and electron transport system.
During glycolysis, energy is released into glucose, and sugar is split into two molecules of pyruvate. There are ten stages in glycolysis:
- phosphorylation of glucose,
- isomerization of glucose-6-phosphate,
- phosphorylation of fructose-6-phosphate,
- cleavage of fructose,
- isomerization of dihydroxyacetone phosphate,
- oxidative phosphorylation of glyceraldehyde 3-phosphate,
- transfer of phosphate from 3-diphosphoglycerate to ADP,
- isomerization of 3-phosphoglycerate,
- dehydration 2-phosphoglycerate,
- transfer of phosphate from phosphoenolpyruvate (Russell et al., 2016).
Glycolysis is the first phase that establishes the foundation for Krebs’ cycle and electron transport system.
Krebs’ cycle occurs in living cells when a series of enzyme-catalyzed reactions contribute to the production of carbon dioxide, the formation of ATP, and the reduction of oxygen. This is the final stage of the aerobic metabolism of fatty acids, proteins, and carbohydrates. According to Russell et al. (2016), there are eight essential stages in the Krebs’ cycle:
- citrate synthase,
- aconitase,
- isocitrate dehydrogenase,
- α-Ketoglutarate dehydrogenase,
- succinyl-CoA synthetase,
- succinate dehydrogenase,
- fumarase,
- malate dehydrogenase.
The electron transport chain is the most important stage because it produces the largest amount of energy and takes place in the mitochondria. Ultimately, via the electron transport chain, NADH turns into ATP. It turns the electron transport chain into a proton pump that accepts electrons at the end of the chain. In Russel et al.’s (2016) book, there are discussed three stages that establish the electron transport chain:
- all electrons are transported from NADH to coenzyme Q,
- from coenzyme Q, electrons are transferred to cytochrome c,
- cytochrome c sends all electrons to oxygen. At the end of the chain, ATP is generated after protons have been pumped through the mitochondrial membrane.
Microbial growth depends on glycolysis, Krebs’ cycle, and electron transport chain because these three processes establish the basis for catabolic glucose attacks and support fermentative metabolism.
Reference
Russell, P. J., Hertz, P. E., & McMillan, B. (2016). Biology: The dynamic science. Nelson Education.