oxidative phosphorylation

• The proton gradient generated by the electron transport chain drives the rotation of ATP synthase, allowing it to catalyze the synthesis of ATP.
• Mitochondria have an outer membrane that is permeable to most metabolites, an inner membrane that is selectively permeable, and a matrix.
• Most mitochondrial proteins are encoded in the nucleus, made in the cytosol and imported into the mitochondria.
• Mitchell’s chemiosmotic theory postulates that the energy from oxidation of components in the respiratory chain is coupled to the translocation of hydrogen ions (protons, H+) from the inside to the outside of the inner mitochondrial membrane.
• The electrochemical potential difference resulting from the asymmetric distribution of the hydrogen ions is used to drive the mechanism responsible for the formation of ATP.
• Electron transport chain ATP synthase uses gradient energy to make ATP.
• NAD+ is a coenzyme that reversibly binds to enzymes.
• FAD is a prosthetic group that remains tightly bound at the active site of an enzyme.
• The inner mitochondrial membrane lacks an NADH transporter, and NADH produced in the cytosol cannot directly enter the mitochondrial matrix.
• Two electrons of NADH are transported from the cytosol into the matrix using substrate shuttles.
• Carbon monoxide and cyanide are the classic poisons that inhibit cytochrome oxidase and can totally arrest respiration.
• The antibiotic oligomycin completely blocks oxidation and phosphorylation by acting on a step in phosphorylation.
• Dinitrophenol is a hydrophobic molecule that remains in the mitochondrial membrane as a chemical uncoupler for a long time, a very dangerous way to burn fat.
• Atractyloside inhibits oxidative phosphorylation by inhibiting the transporter of ADP into and ATP out of the mitochondrion.
• Barbiturates, Antimycin A, Dimercaprol, Carbon monoxide, and Cyanide can totally arrest respiration.
• Barbiturates, Antimycin A, Dimercaprol, Carbon monoxide, and Cyanide are inhibitors of the respiratory chain.
• These compounds are toxic in vivo, causing respiration to become uncontrolled, since the rate is no longer limited by the concentration of ADP or Pi.
• Uncouplers of oxidative phosphorylation dissociate oxidation in the respiratory chain from phosphorylation.
• In the glycerol 3-phosphate shuttle, two electrons are transferred from NADH to dihydroxyacetone phosphate by cytosolic glycerol phosphate dehydrogenase.
• Hemes in the 3 classes of cytochrome (a, b, c) differ slightly in substituents on the porphyrin ring system.
• The structure of Co Q is very similar to that of vitamin K and vitamin E and of plastoquinone, found in chloroplasts.
• Hemes a and a3 are often referred to as cytochromes aa3.
• 24Malate - aspartate shuttle, produces NADH (rather than FADH2) in the mitochondrial matrix.
• Co Q acts as a mobile component of the respiratory chain that collects reducing equivalents from the more fixed flavoprotein complexes and passes them on to the cytochromes.
• Cytochrome c is a small, water-soluble protein with a single heme group.
• Complexes I to IV each contain part of the electron transport chain, whereas complex V catalyzes ATP synthesis.
• The electron transport chain (ETC) can be organized into five separate enzyme complexes: I, II, III, IV, and V.
• Cytochromes (Cyt) are proteins with heme prosthetic groups that absorb light at characteristic wavelengths.
• Coenzyme Q functions as a mobile e-carrier within the mitochondrial inner membrane.
• A transport protein carries malate into the matrix.
• Coenzyme Q (CoQ, ubiquinone) is very hydrophobic and dissolves in the membrane.
• The glycerol 3-phosphate produced is oxidized by the mitochondrial isozyme as FAD is reduced to FADH2.
• These mitochondria have a unique protein in their inner membrane called thermogenin or uncoupling protein that provides a path for protons to return to the mitochondrial matrix without going through the ATP synthase complex.
• The inner mitochondrial membrane is freely permeable to uncharged small molecules, such as oxygen, water, CO2, and NH3, and monocarboxylic acids, such as 3-hydroxybutyric, acetoacetic, and acetic acid.
• Oxidation and phosphorylation are tightly coupled; oxidation cannot proceed via the respiratory chain without concomitant phosphorylation of ADP.
• Many poisons inhibit the respiratory chain.
• In newborns and hibernating animals, there is a type of adipose tissue known as brown fat which serves to generate heat to keep the newborn warm.
• These compounds may be classified as inhibitors of the respiratory chain, inhibitors of oxidative phosphorylation, and uncouplers of oxidative phosphorylation.
• The tissue is brown due to the large numbers of mitochondria which have large amounts of cytochromes whose heme groups strongly absorb light.
• Scattered over the surface of the inner membrane are the phosphorylating complexes, ATP synthase, responsible for the production of ATP.