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Pyruvate Oxidation or Oxidative Decarboxylation (if oxygen is present…) The following occurs for each pyruvate: 1. CO2 removed. 2. NAD+ reduced to NADH and the 2-carbon compound becomes acetic acid. 3. Coenzyme A (CoA) attaches to acetic acid to form acetyl-CoA. Pyruvate Oxidation or Oxidative Decarboxylation Pyruvate Oxidation or Oxidative Decarboxylation Energy Yield & Products: 2 NADH 2 acetyl-CoA 2 CO2 (released as waste) Acetyl-CoA CoA comes from vitamin B5 Proteins, lipids, and carbohydrates are catabolized to ‘acetyl-CoA’ It can be used to make fat or ATP [ATP] determines what pathway this molecule takes If O2 is present, ‘acetyl CoA’ moves to the Kreb’s Cycle (aerobic respiration) If O2 is NOT present, ‘acetyl CoA’ becomes ‘lactate’ (anaerobic respiration / fermentation) Krebs cycle - overview 8 step process, with each step catalyzed by a specific enzyme It is a ‘cycle’ because oxaloacetate is the product of step 8, and the reactant in step 1 REMEMBER: Two acetyl-CoA molecules enter, so the Krebs Cycle must happen TWICE for every one molecule of glucose that begins glycolysis The Krebs Cycle Occurs twice for each molecule of glucose, 1 for each acetyl-CoA. The Krebs Cycle – Key Features 1. 2. 3. 4. 5. 6. In step 1, acetyl-CoA combines with oxaloacetate to form citrate. NAD+ is reduced to NADH in steps 3, 4 and 8. FAD is reduced to FADH2 in step 6. ATP if formed in step 5 by substrate-level phosphorylation. The phosphate group from succinylCoA is transferred to GDP, forming GTP, which then forms ATP. In step 8, oxaloacetate is formed from malate, which is used as a reactant in step 1. CO2 is released in steps 3 and 4. The Krebs Cycle Energy Yield & Products: 2 ATP 6 NADH 2 FADH2 4 CO2 (released as waste) NADH and FADH2 carry electrons to the electron transport chain for further production of ATP by oxidative phosphorylation. Cellular Respiration so far has produced… Glycolysis 2 ATP (net) 2 NADH, converted to 2 FADH2 Pyruvate Oxidation 2 NADH Krebs Cycle 2 ATP 6 NADH 2 FADH2 E.T.C. - Structure A series of electron acceptors (proteins) are embedded in the inner mitochondrial membrane. These proteins are arranged in order of increasing electronegativity. The weakest attractor of electrons (NADH dehydrogenase) is at the start of the chain and the strongest (cytochrome oxidase) is at the end. Since the mitochondrial membrane is highly folded, there are multiple copies of the ETC across the membrane Electron Transport Chain - Overview NADH and FADH2 transfer electrons to proteins in the inner mitochondrial membrane The weakest electron attractors are at the start, and the strongest are at the end Each component is REDUCED, and then subsequently OXIDIZED Oxygen (highly electronegative) oxidizes the last ETC component The energy released, moves H+ atoms (i.e. protons) across mitochondrial membrane Electrochemical gradient is created, with a lot of H+ outside Sets the rate of this process… The energy stored in the [] gradient will be used in the second part of the ETC to power ATP synthesis