Cellular respiration is the cell's way of using glucose from food to make energy in the form of ATP. There are many metabolic pathways that a cell can rely on for energy. Collectively, these metabolic pathways make up cellular respiration. Consisting of a series of chemical reactions that primarily operate under aerobic conditions (those requiring air or oxygen), cellular respiration includes glycolysis, the citric acid cycle, an electron transport chain, and chemiosmosis. When cells are deprived of oxygen, they can still get energy using a different process called fermentation.
At A Glance
- When oxidation and reduction reactions occur together, they drive many of the metabolic pathways in cellular respiration used to produce energy for the cell.
- In cellular respiration, glucose and oxygen react to form carbon dioxide, water, and energy.
- A small class of compounds binds and carries high-energy electrons between compounds during the different pathways involved in cellular respiration.
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Glycolysis is the first pathway used by the cell to break down glucose for energy.
- The first half of glycolysis is the energy-investing phase.
- The second half of glycolysis is the energy-harvesting phase.
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Pyruvate, produced during glycolysis, must be processed in order to drive other metabolic pathways.
- The citric acid cycle consists of a series of steps used to catalyze products following the oxidation of pyruvate.
- The citric acid cycle starts after the oxidation of pyruvate. It consists of eight sequential steps that use the products of one reaction as the reactants of the next. The end result is the production of NADH and the reformation of oxaloacetate, which is then recycled to start the cycle over again.
- The citric acid cycle uses multiple reactions for the release of energy.
- Occurring only in the presence of oxygen and with the help of a proton gradient, the cell uses oxidative phosphorylation to produce large amounts of energy in the form of ATP.
- In the electron transport chain, electrons are transferred between electron carriers through protein complexes and protons are pumped out of the mitochondria.
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Chemiosmosis uses the process of ion diffusion across a selectively permeable membrane.
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Fermentation produces two ATP molecules without oxygen.
