Electron Transport and Oxidative Phosphorylation PDF

# Electron Transport and Oxidative Phosphorylation ## Electron Transport The transport of electrons from enzymatic cofactors (NADH, FADH2) to oxygen. ## Oxidative Phosphorylation The use of energy from transporting electrons from (NADH,FADH2) to oxygen to produce ATP. ## Respiratory Chain * H...

# Electron Transport and Oxidative Phosphorylation ## Electron Transport The transport of electrons from enzymatic cofactors (NADH, FADH2) to oxygen. ## Oxidative Phosphorylation The use of energy from transporting electrons from (NADH,FADH2) to oxygen to produce ATP. ## Respiratory Chain * Hydrogen and electrons flow through the respiratory chain from NAD/NADH to O2/H2O. * The respiratory chain consists of a number of redox carries that produce from NAD linked dehydrogenises systems, through flavoproteins and cytochromes to molecular oxygen. ## Components of the Respiratory Chain The following components are involved: * Proline * 3-Hydroxyacyl-CoA * 3-Hydroxybutyrate * Glutamate * Malate * Isocitrate * Succinate * Choline * Pyruvate * Lipoate * α-Ketoglutarate * Fp (FAD) * FeS * NAD * Q * Cyt b * Cyt c1 * Cyt c * Cyt aa3O2 * Cu * ETF * Fp (FAD) * Fp (FMN) * Fp (FAD) * FeS: Iron-sulfur protein * ETF: Electron-transferring flavoprotein * Fp: Flavoprotein * Q: Ubiquinone * Glycerol 3-phosphate * Acyl-CoA * Sarcosine * Dimethylglycine * Cyt: Cytochrome ## Detail Steps ### A- Oxidation of NADH The oxidation of one molecule of NADH produces three molecules of ATP. The equation is: $NADH + H^+ + 3ADP + 3Pi + ½ O_2 → NAD + 3ATP + H_2O$ ### B- Oxidation of FADH2 The oxidation of one molecule of FADH2 produces two molecules of ATP. The equation is: $FADH_2 + 2ADP + 2Pi + ½ O_2 → FAD + 2ATP + H_2O$ ## The aim of the pathway * Production of energy as (ATP) by oxidation of NADH and FADH2. * Production of oxidize forces as NAD, FAD. ### 1. Electron Flow from NADH * Electrons of NADH start to enter the respiratory chain from the NAD-specific dehydrogenises through flavoproteins and cytochromes to molecular oxygen. ### 2. Electron Flow from FADH2 * Electrons of FADH2 start to enter the respiratory chain from coenzyme Q forming hydroquinone QH2, after that these electrons transfer to other respiratory chain parts. * (fumarate/succinate) are linked directly to flavoproteins dehydrogenises, because their rodex potentials are more positive than the NAD-specific dehydrogenises. ### 3. ATP Production * ATP molecules produce in three sites in NADH molecules and in two sites in FADH2 molecule, (as a result of phosphorylation of ADP molecules. * $ADP + Pi → ATP$ ## Sites of ATP Production * **The first site:** between NADH and CoQ. * **The second site:** between cytochrome b and c. * **The third site:** between cytochrome c and oxygen. ## The Hypothesis of Oxidative Phosphorylation ### 1. Chemical Coupling Hypothesis This hypothesis postulates that during electron transfer from redox forces to oxygen forms intermediate compound (a high-energy compound). This compound is used as a precursor to form a phosphatic bond with high energy (to form ATP from ADP and phosphate). ### 2. Chemiiosomotic Hypothesis This postulates that the mitochondria membrane is impermeable to protons, thus, electrons transporting from one carrier to another cause in transporting of protons to out, as a result, the respiratory chain serves as a (pump) to transport H+ ions from the mitochondria and drive the synthesis of ATP. ### 3. Conformational Change in Protein Boyer postulated that electron transport is conserved in the form of a conformational change in an electron carrier protein molecule, and this change will yield energy as ATP. ## Transporting of NADH in and out of mitochondria NADH cannot penetrate the mitochondria membrane, but it is produced in the cytosol by 3-phosphoglyceraldehyde dehydrogenase in glycolysis. ## The Mechanism of Transfer Using the Glycerophosphate Shuttle and the Malate Shuttle ### Malate Shuttle In this shuttle, the electrons transfer from NADH to oxaloacetate which is reduced to malate by malate dehydrogenase. Then, malate enters to mitochondria, after that, malate reduces NAD to NADH and converts to oxaloacetate by malate dehydrogenase. Oxaloacetate converts to aspartate which transports through the mitochondria membrane and converts to oxaloacetate in the cytosol. (oxaloacetate reacts with glutamate and produces aspartate and NADH by aminotransferase in the cytosol). NADH enters oxidation phosphorylation, and the oxidation of NADH in this shuffle produces three molecules of ATP. This shuttle takes place in the heart, kidneys and liver. * **Diagram:** * **Cytosol:** NAD+ is converted to NADH, then oxaloacetate is converted to malate by malate dehydrogenase. * **Inner Membrane:** Malate is transported into the mitochondria, where it is oxidized to oxaloacetate, reducing NAD+ to NADH. * **Mitochondrion:** Oxaloacetate is converted to aspartate which is transported back to the cytosol, where it is converted back to oxaloacetate.