oxidative phosphorylation

Examples of oxidative phosphorylation in the following topics:

• Chemiosmosis and Oxidative Phosphorylation

  • The production of ATP using the process of chemiosmosis in mitochondria is called oxidative phosphorylation.
  • In oxidative phosphorylation, the hydrogen ion gradient formed by the electron transport chain is used by ATP synthase to form ATP.

• 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.

• Electron Transport Chain

  • The electron transport chain uses the electrons from electron carriers to create a chemical gradient that can be used to power oxidative phosphorylation.
  • Oxidative phosphorylation is a highly efficient method of producing large amounts of ATP, the basic unit of energy for metabolic processes.
  • As a result, the iron ion at its core is reduced and oxidized as it passes the electrons, fluctuating between different oxidation states: Fe2+ (reduced) and Fe3+ (oxidized).

• 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.

• Importance of Glycolysis

  • Glycolysis is the first pathway of cellular respiration that oxidizes glucose molecules.
  • It is followed by the Krebs cycle and oxidative phosphorylation to produce ATP.

• 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.

• The Energy-Releasing Steps of Glycolysis

  • The sugar is then phosphorylated by the addition of a second phosphate group, producing 1,3-bisphosphoglycerate.
  • The continuation of the reaction depends upon the availability of the oxidized form of the electron carrier NAD+.
  • Thus, NADH must be continuously oxidized back into NAD+ in order to keep this step going.
  • (This is an example of substrate-level phosphorylation. ) A carbonyl group on the 1,3-bisphosphoglycerate is oxidized to a carboxyl group, and 3-phosphoglycerate is formed.
  • The second half of glycolysis involves phosphorylation without ATP investment (step 6) and produces two NADH and four ATP molecules per glucose.

• Connecting Lipids to Glucose Metabolism

  • Glycerol can be phosphorylated to glycerol-3-phosphate, which continues through glycolysis.
  • Fatty acids are catabolized in a process called beta-oxidation that takes place in the matrix of the mitochondria and converts their fatty acid chains into two carbon units of acetyl groups, while producing NADH and FADH2.

• Biosynthetic Mechanisms

  • Subsequent reactions effect an oxidative cleavage of glucose to pyruvic acid (CH3COCO2H), and this in turn is transformed to the two-carbon building block, acetate.
  • Consequently, the condensation, alkylation, oxidation and reduction reactions that accomplish the biosynthesis of lipids will not make use of the very strong bases, alkyl halides, chromate oxidants or metal hydride reducing agents that are employed in laboratory work.
  • The reduction steps (designated by [H] in the equations) and the intervening dehydrations needed for fatty acid synthesis require unique coenzymes and phosphorylating reagents.
  • The chief biological phosphorylation reagents are phosphate derivatives of adenosine (a ribose compound).
  • Phosphorylation and elimination of mevalonic acid then generate isopentenyl pyrophosphate, which is in equilibrium with its double bond isomer, dimethylallyl pyrophosphate.