oxidative phosphorylation

Examples of oxidative phosphorylation in the following topics:

• Fermentation Without Substrate-Level Phosphorylation

  • Fermentation is the process of extracting energy from the oxidation of organic compounds such as carbohydrates.
  • Even in the presence of abundant oxygen, yeast cells greatly prefer fermentation to oxidative phosphorylation, as long as sugars are readily available for consumption (a phenomenon known as the Crabtree effect).
  • Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound.
  • Fermentation is important in anaerobic conditions when there is no oxidative phosphorylation to maintain the production of ATP (adenosine triphosphate) by glycolysis.
  • For example, even in the presence of abundant oxygen, yeast cells greatly prefer fermentation to oxidative phosphorylation, as long as sugars are readily available for consumption (a phenomenon known as the Crabtree effect).

• Acetyl CoA and the Citric Acid Cycle

  • The citric acid cycle, shown in —also known as the tricarboxylic acid cycle (TCA cycle) or the Krebs cycle—is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate—derived from carbohydrates, fats, and proteins—into carbon dioxide.
  • The NADH generated by the TCA cycle is fed into the oxidative phosphorylation pathway.
  • The net result of these two closely linked pathways is the oxidation of nutrients to produce usable energy in the form of ATP.
  • The NADH and QH2 that is generated by the citric acid cycle is used by the oxidative phosphorylation pathway to generate energy-rich adenosine triphosphate (ATP).
  • The citric acid cycle, or Krebs cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidization of acetate—derived from carbohydrates, fats, and proteins—into carbon dioxide.

• Respiration and Proton Motive Force

  • During aerobic conditions, the pyruvate enters the mitochondrion to be fully oxidized by the Krebs cycle.
  • Both types of metabolism share the initial pathway of glycolysis, but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation.
  • The initial phosphorylation of glucose is required to destabilize the molecule for cleavage into two pyruvate.
  • During the pay-off phase of glycolysis, four phosphate groups are transferred to ADP by substrate-level phosphorylation to make four ATP, and two NADH are produced when the pyruvate are oxidized.
  • The overall process of creating energy in this fashion is termed oxidative phosphorylation.

• Anoxygenic Photosynthesis

  • This restricts them to cyclic electron flow and are therefore unable to produce O2 from the oxidization of H2O.
  • In the process, it will generate a proton motor force (PMF) which can then be used to synthesize ATP by oxidative phosphorylation.
  • Therefore electrons are not left over to oxidize H2O into O2.

• Proton Reduction

  • Reduction occurs when an oxidant gains an electron.
  • This potential energy is used for the synthesis of ATP by phosphorylation.
  • The overall process of creating energy in this fashion is termed oxidative phosphorylation.
  • Instead, it only uses substrate-level phosphorylation to produce ATP.
  • The electron acceptor NAD+ is regenerated from NADH formed in oxidative steps of the fermentation pathway by the reduction of oxidized compounds.

• Anoxygenic Photosynthetic Bacteria

  • This restricts them to cyclic electron flow; they are therefore unable to produce O2 from the oxidization of H2O.
  • Instead, they use hydrogen sulfide, which is oxidized to produce granules of elemental sulfur.
  • This in turn may be oxidized to form sulfuric acid.The purple sulfur bacteria are divided into two families: the Chromatiaceae and Ectothiorhodospiraceae, which respectively produce internal and external sulfur granules, and show differences in the structure of their internal membranes.
  • In the process, it will generate a proton motor force (PMF) which can then be used to synthesize ATP by oxidative phosphorylation.

• Large-Scale Fermentations

  • Fermentation includes the processes by which energy is extracted from the oxidation of organic compounds.
  • The oxidation of organic compounds occurs by utilizing an endogenous electron acceptor to transfer electrons released from nutrients to molecules obtained from the breakdown of these same nutrients .
  • Fermentation can be carried out in aerobic conditions as well, as in the case of yeast cells which prefer fermentation to oxidative phosphorylation.

• Proteomics

  • Not only does the translation from mRNA cause differences, but many proteins are also subjected to a wide variety of chemical modifications after translation which are critical to the protein's function such as phosphorylation, ubiquitination, methylation, acetylation, glycosylation, oxidation, and nitrosylation.
  • For example, some proteins are not active until they become phosphorylated.
  • For example, there are antibodies that only recognize certain proteins when they are tyrosine-phosphorylated, known as phospho-specific antibodies.

• Syntrophy

  • This means that these organisms do not use an electron transport chain to oxidize NADH to NAD+ and therefore must have an alternative method of using this reducing power and maintaining a supply of NAD+ for the proper functioning of normal metabolic pathways (e.g. glycolysis).
  • Instead of using an ATP synthase as in respiration, ATP in fermentative organisms is produced by substrate-level phosphorylation where a phosphate group is transferred from a high-energy organic compound to ADP to form ATP.
  • The best studied example of syntrophy in microbial metabolism is the oxidation of fermentative end products (such as acetate, ethanol and butyrate) by organisms such as Syntrophomonas.
  • Alone, the oxidation of butyrate to acetate and hydrogen gas is energetically unfavorable.
  • However, when a hydrogenotrophic (hydrogen-using) methanogen is present the use of the hydrogen gas will significantly lower the concentration of hydrogen (down to 10−5 atm) and thereby shift the equilibrium of the butyrate oxidation reaction under standard conditions (ΔGº) to non-standard conditions (ΔG').

• Regulation of the Calvin Cycle

  • RuBisCO enzymatic activity is regulated by numerous factors including: ions, RuBisCO activase, ATP/ADP and reduction/oxidation states, phosphate and carbon dioxide.