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Cellular Respiration Part 2: The Transition Reaction Part 3: Krebs Cycle

Cellular Respiration Part 2: The Transition Reaction Part 3: Krebs Cycle. Part 2: Transition Reaction. Remember, glycolysis took a 6 carbon glucose molecule and produced two 3 carbon pyruvates , a net of 2 ATP molecules, H 2 O and NADH

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Cellular Respiration Part 2: The Transition Reaction Part 3: Krebs Cycle

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  1. Cellular RespirationPart 2: The Transition ReactionPart 3: Krebs Cycle

  2. Part 2: Transition Reaction • Remember, glycolysis took a 6 carbon glucose molecule and produced two 3 carbon pyruvates, a net of 2 ATP molecules, H2O and NADH • In this step the end products of glycolysis, the 2 pyruvate molecules, are moved from the cytoplasm into the mitochondria for further energy “harvesting”.

  3. TRANSITION REACTION • this occurs across both the outer and inner mitochondrial membranes • Decarboxylation • NAD+ reduced to energized NADH + H+ • coenzyme A added to pyruvate forming AcetylCoA

  4. Part 3: Krebs Cycle • This is also called the Citric Acid Cycle or the Tricarboxylic Acid Cycle (TCA) • The purpose is to slowly oxidize a pyruvate molecule and “harvest” the bond energy in small amounts • The energy released in the catabolism of the pyruvate is stored in NADH, FADH2 and ATP via GTP (guanine triphosphate)

  5. 1. KREBS CYCLE starts • acetyl CoA bonds to 4C oxaloacetate forming a 6C citrate • a water is required • the coenzyme A is released to be reused

  6. 2. Isomerization - This happens so the next reaction requires less energy

  7. 3. Harvest Energy • Decarboxylation • an NAD+ is reduced to an energized NADH + H+ • this is from the energy “harvested” during the decarboxylation and oxidation of isocitrate

  8. 4. More Energy is “Harvested” • Decarboxylation • another NAD+ is reduced to NADH + H+ • this is from the energy “harvested” during the decarboxylation and the oxidation of  ketoglutarate • note again the addition of a coenzyme A to the product

  9. 5. Harvest More Energy • The release of the coenzyme A and the isomerization provides energy to phosphorylate a GDP to a GTP • The GTP is used to phosphorylate an ADP to an ATP • these are both examples of substrate level phosphorylation, where the phosphorylation energy comes from breaking the bonds of another molecule

  10. 6. It’s all about the energy STOOPID!! • FAD is reduced to an energized FADH2 • the energy comes from oxidation of succinate • another coupled redox reaction!!

  11. 7. What Energy? - adding a water hydrolyses the double bond

  12. 8. Yeah – More Energy!! • again an NAD+ is reduced to energized NADH + H+ • the 4 carbon oxaloacetate molecule is regenerated • Note that of the 3 CO2 molecules generated only the first one actually removed a carbon from the original pyruvate • The 2nd and 3rd carbons removed were from previous pyruvate molecules

  13. Transition Reaction and Krebs Cycle - SUMMARY For each molecule of pyruvate the Krebs Cycle turned once and: • Required 2 H2O and CoA • Generated 1 ATP, 4 NADH, 1 FADH2, 4H+ and released 3 CO2 Double all these products for a glucose!

  14. Finally, For a test you will be given the Krebs Cycle with the main molecules and you will have to name reactions and complete all the molecules on the coupled reaction arrows. Next, how does the cell get ATP energy from the energized NADH and FADH2?

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