Aerobic Respiration

1. Aerobic Respiration with K-Mart, S-Fin, P.G. Love, Shaq, Killa-K, and Joe Barbado occasionally gracing us with his presence

2. Aerobic Respiration Info Occurs after Glycolysis Occurs in the presence of oxygen Oxygen is excellent election acceptor Produces significant amounts of ATP Net Gain:36 ATP

3. Statges Aerobic Respiration occurs in 3 basic stages: The Oxidation of Pyruvate The Kreb's Cycle The Electron Transport Chain

4. The Oxidation of Pyruvate into Acetyl-Coa

5. Basic Information Reaction has 3 intermediate stages Occurs in mitochondria Catalyzed by multienzyme complex Pyruvate dehydrogenase Called the “link” reaction because it is the step between glycolysis and the Kreb's cycle

6. Step 1 Pyruvate is oxidized in a decarboxylation reaction This removes one of the three carbon atoms The carbon atom is removed as CO2

7. Step 2 The remaining two carbon group is called an acetyl group It is attached to coenzyme A This creates Acetyl-CoA

8. Step 3 A pair of electrons and one proton are added NAD+ is reduced to NADH

9. Reaction Summary Pyruvate + NAD+ + CoA ? acetyl-CoA + NADH + CO2 + H+

10. The Krebs Cycle

11. KREBS CYCLE The pyruvate molecules produced during glycolsis contain a lot of energy, in the bonds between their molecules. In order to use that energy, the cell must convert it into the form of ATP To do so, pyruvate molecules are processed through the Krebs cycle, also known as the CITRIC CYCLE.

12. KREBS CYCLE CONT. Krebs Cycle is the 2nd stage of anaerobic respiration In this cycle, the 2- carbon acetyl group of acetyl CoA combines with a four – carbon molecule called oxloacetate. The resulting six carbon molecule, citrate, then goes through a several step sequence of electron yielding oxidation reactions, during which two CO2 molecules split off, restoring oxloacetate.

13. SEGMENTS The 9 reactions of the Krebs cycle can be grouped into three overall segmemts

14. Segment A:Acetyl- CoA plus Oxaloacetate Produces 6 Carbon citrate molecules Pyruvate from glycolysis is oxidized into an acetyl group that feeds into the citric acid cycle. 2-C acetyl group combines with 4-C oxaloacetate to produce 6-C compound citric acid.

15. Segment B:Citrate Rearrangement and Decarboxylation Reduces citrate to a 5 carbon intermediate then to a 4 carbon succinate During reaction 2 NADH are produce, oxidation reduction produces the NADH The loss of two co2’s leaves a new 4-C compound 1 ATP is directly generated for each acetyl group fed in

16. Segment C: Regeneration of Oxaloacetate Succinate undergoes 3 additional reactions to become oxaloacetate. During theses reactions 1 NADH is produced and 1 molecule of FAD is also produced FAD- FLAVIN ADENINE DINUCLEOTIDE Another cofactor becomes reduced to FADH2

17. KREB CYCLE REATIONS The Krebs cycle is broken down into 9 individual reaction groups. In the reactions A 2- carbon group from acetyl-CoA enters the cycle at the beginning, and two Co2 molecules, on ATP, and four pairs of electrons are produced.

18. Reaction 1: Condensation Citrate is formed from acetyl- CoA The condensation reaction is irreversible This reaction occurs when the cell’s ATP concentration is high and stimulated when it is low Results: when there is enough ATP the Krebs Cycle shuts down and acetyl- CoA is channeled into Fat synthesis Citric acid synthetaste Acetyl Co-A + OAA Citric Acid

19. Reaction 2: Isomerization The Hydroxyl group of citrate must be repositioned before oxidation can start. A water molecule is then removed from carbon.

20. Reaction 3: Isomerization Water is then added to a different carbon Resulting with an –H group and, an –OH group repositioning. The final product is an isomer of citrate called Isocitrate.

21. Reaction 4: The First Oxidation This is the first energy yielding step of the cycle. Isocitrate undergoes and oxidative decarboxylation reaction. Isocitrate is oxidized producing a pair of electrons that reduce a molecule of NAD to NADH The oxidized intermediate is decarboxylated; the central carboxyl group split off to form Co2, yielding a 5-carbon molecule called a ketoglutarate.

22. Segment 5: The Second Oxidation Next a Ketoglutarate is decarboxylated by mulitienzyme complex similar to Pyruvate dehydrogenase. The succinyl group left after the removal of Co2 joins to coenzyme A, forming succinyl-CoA. In the process two electrons are extracted, and they reduce another molecule of NAD to NADH

23. Reaction 6: Substrate – Level Phoshorylation The linkage between the 4 Carbon succinyl group and CoA is a high energy bond. This bond is cleaved and the energy released drives the GDP (Phoshorylation of guanosine diphosphate) forming guanosine triphosphate GTP can transfer a phosphate to ADP converting it into ATP. The 4 Carbon molecule that remains is called succinate.

24. Reaction 7: The 3rd Oxidation Succinate is oxidized to fumarate by an enzyme located in the inner mitochondrial membrane. Free energy change is not large enough to reduce NAD, instead, FAD is the electron acceptor. Unlike NAD, FAD is not free to diffuse within the mitochondrion; it is tightly associated with its enzyme in the inner mitochondrial membrane. Its reduced form, FADH2 can only contribute electrons to the electron transport chain in the membrane.

25. Reaction 8 & 9: Regeneration of Oxaloacetate In the final two reactions, a water molecule is added to fumarate, forming malate. Malate an intermediate in the citric acid cycle Malate is then oxidized, yielding a 4 carbon molecule of oxaloacetate and 2 electrons that reduce a molecule of NAD to NADH. Oxaloacetate ( the molecule that began the cycle) is now free to combine with another 2 carbon acetyl group from acetyl CoA and reinitiate the cycle.

26. The Krebs Cycle completes the oxidation of glucose begun with glycolysis. Units of the 2 carbon molecule acetyl CoA are added to the 2 Carbon molecule oxloacetate to produce citric acid. The cycle then uses a series of oxidation, decarboxylation, and rearrangement reactions to return to oxloacetate. This process produces NADH and FADH2 which provides electrons and protons for the electron transport chain. Also produces one ATP per turn of the Cycle.

27. Electron Transport Chain

28. Electron Transport Chain The NADH and FADH2 molecules formed during the first two stages of aerobic respiration each contain a pair of electrons that were gained when NAD? and FAD were reduced. The NADH molecules carry their electrons to the inner mitochondrial membrane, where they transfer the electrons to a series of membrane-associated proteins collectively called the electron transport chain (ETC)

29. Moving Electrons Through the ETC The first of the proteins to receive the electrons is a complex, membrane-embedded enzyme called NADH dehydrogenase A carrier called ubiquinone then passes the electrons to a protein-cytochromes complex called the bc1 complex. This complex along with others in the chain operate as a protein pump by driving a protein out across the membrane. Cytochromes are respiratory proteins that contain heme groups, complex carbon rings with many alternating single and double bonds and an iron atom in the center.

30. Moving Electrons Through the ETC Con’t The electron is then carried by another carrier cytochrome c, to the cytochrome oxidase complex. This complex uses four such electrons to reduce a molecule of oxygen, each oxygen then combines with two hydrogen ions to form water O2+4H?+4e? 2H2O This series of membrane-associated carriers is collectively called the ETC

31. Moving Electrons Through the ETC Con’t NADH contributes it electrons to the first protein of the ETC, NADH dehydrogenase. FADH2 which is always attached to the inner mitochondrial membrane, feeds its electrons into the electron transport chain later to ubiquinone.

32. ETC cont. Mitochondrion contains the enzymes that carry out the reactions of the Krebs cycle. Energy that electrons release transport protons out of matrix into intermembrane space Electrons contributed by NADH activate all three of proton pumps, while those contributed by FADH2 activate only two.

33. Chemiosmosis Intermembrane space rises above that in the matrix, becomes slightly negatively charged. This attracts protons and induces them to reenter the matrix. The greater the outer concentration tends to drive protons back by diffusion; since membranes relatively impermeable to ions.

34. Chemiosmosis Cont. Protons pass through special channels in inner mitochondrial membrane. Protons pass through, then these channels synthesize ATP from ADP + Pi within the matrix. ATP transported by facilitate diffusion out of mitochondria into cytoplasm. ATP chemical formation is driven by diffusion force similar to osmosis, process called chemiosmosis.

35. Chemiosmosis Cont. Electrons harvested in aerobic respiration are used to pump a large number of protons across inner mitochondrial membrane. Their reentry into mitochondrial matrix drives synthesis of ATP by chemismosis.