Pyruvate Oxidation and Krebs Cycle PART 1: ANAEROBIC RESPIRATION

1. Pyruvate Oxidation and Krebs CyclePART 1: ANAEROBIC RESPIRATION

2. PYRUVATE OXIDATION Homework: Read p.126, 127 and make notes on pyruvate oxidation and Kreb’s

3. 3 Pathways for Pyruvate • In the absence of oxygen (anerobic respiration): 1) Lactic acid (lactate) fermentation 2) Alcoholic fermentation • In the presence of oxygen (aerobic respiration): 3) Entrance into the Krebs Cycle

4. Anaerobic Pathways When oxygen is not available Eukaryotes still carry out glycolysis by transferring the H atoms in NADH to pyruvate The NAD+ molecules formed allow glycolysis to continue Turn to P. 135

5. Ethanol (Alcohol) Fermentation Occurs in yeast cells and is used in wine, beer, and bread making

7. 1) Ethanol (Alcohol) Fermentation CO2 is removed from pyruvate, and beocmes acetaldehyde The acetaldehyde is reduced to ethanol by attaching H from NADH (oxidized) FINAL PRODUCTS: ATP, CO2, ethanol Enables more NAD+ is available for glycolysis Generally not reversible

9. A particular organism releases carbon dioxide and alcohol as its end products. The organism is most likely which of the following? a. an animal b. an alga c. a green plant d. a yeast e. a virus d. a yeast

10. Anaerobic and aerobic respiration are similar in all but one of the following ways. Which one is the exception? A) NAD+ is reduced B) carbon dioxide is a product C) ADP is combined with inorganic phosphate to form ATP D) acetaldehyde is converted into ethanol E) both can release energy from glucose D) acetaldehyde is converted into ethanol

11. 2) Lactate (lactic acid) fermentation Occurs in animal muscle cells during strenuous exercise Reversible Involves the oxidation of NADH and the reduction of pyruvate FINAL PRODUCTS: ATP, lactate

14. What happens to lactic acid after it is formed in a muscle cell? Lactic acid travels in the bloodstream to the liver, where it is oxidized back to pyruvate, which then goes through the Krebs cycle and oxidative phosphorylation. The presence of lactic acid in the muscle tissues leads to stiffness, soreness, and fatigue.

15. Oxygen debt Oxygen debt refers to the extra oxygen required by the liver to oxidize lactic acid to CO2 and water (through the aerobic pathway) Panting “pays” for the oxygen debt

16. During active exercise, the supply of oxygen becomes inadequate for the level of activity you are attempting to maintain. How do the catabolic reactions of the cell continue? Glycolysis continues to supply small amount of ATP, and the pyruvate that normally would continue on the Krebs cycle as acetyl-CoA is instead converted to lactate to regenerate NAD+ to allow glycolysis to continue.

17. VO2 max and the Lactate Threshold The maximum oxygen uptake (VO2 max) is the maximum volume of oxygen that the cells of the body can remove from the bloodstream in one minute per kg of body mass while the body experiences max. exertion. The lactate threshold (LT) is the value of exercise intensity at which blood lactate concentration begins to increase sharply.

18. Stage 2:Pyruvate Oxidation If oxygen is present, the pyruvate will undergo further breakdown and release more energy. The 3-C pyruvate enters the mitochondrion. Pyruvate oxidation occurs in the inner membrane of the mitochondrion.

19. PYRUVATE OXIDATION

20. Pyruvate Oxidation has three parts: 1)decarboxylation reaction-- CO2 is released 2)Redox reaction--NAD+ is reduced to NADH + H+ 3) 2-carbon acetyl group combines with coenzyme A to form acetyl-CoA. This acetyl-CoA entersthe Kreb's cycle. Pyruvate + NAD+ + CoA==> Acetyl-CoA + NADH + CO2

21. Krebs CycleSir Hans Krebs, who won a Nobel Prize for its discovery, preferred the term “Tricarboxylic Acid Cycle” (TCA cycle) Homework: Answer p.147 #4-9; 28, 40, 41, 50

23. ANIMATION! http://www.science.smith.edu/departments/Biology/Bio231/krebs.html

24. STAGE 1 OF AEROBIC RESPIRATION: THE KREBS CYCLE

27. Stage 3: The Krebs Cycle In this process, each of the two-carbon acetyl-CoA molecules is combined with a 4-C compound called oxaloacetate to produce a 6-C citrate molecule. These citrate molecules are then oxidized to a 5-C compound plus carbon dioxide. They are then further oxidized to a 4-C compound plus carbon dioxide. The 4-C compound is then transformed back to oxaloacetate so that the cycle can begin again.

28. Note: each of the 3 carbon atoms present in the pyruvate that entered the mitochondrion leaves as a molecule of carbon dioxide (CO2) at 3 steps in the cycle, a pair of electrons (2e-) is removed and transferred to NAD+ reducing it to NADH + H+ At one step, a pair of electrons is removed from succinic acid and reduces FAD to FADH2

29. Summary of Kreb's cycle: 2 carbon dioxide molecules are released, 3 pairs of H atoms are picked up by NAD+, 1 pair of H atoms are picked up by FAD 2 molecules of water are used, 1 molecule of ATP is formed and a molecule of oxaloacetate is left to start the cycle all over again.

30. Remember, there are 2 molecules of pyruvate formed from each molecule of glucose, therefore the cycle runs twice for each glucose molecule. Almost all the chemical energy extracted from the pyruvate is carried by the hydrogen and temporarily transferred to the reduced coenzymes.

31. #10. Describe the function of NAD+ and FAD in cellular respiration. They act as coenzymes that harvest energy from the reactions of glycolysis, pyruvate oxidation, and the Krebs cycle and carry it to power ATP synthesis by oxidative phosphorylation.

32. NAD+ is used to shuttle electrons to the first component of the ETC. During oxidative phosphorylation, NAD+ removes 2 hydrogen atoms from a part of the original glucose molecule. Two electrons and one proton attach to NAD+, reducing it to NADH (NAD+ is the oxidized form of NADH). This reduction occurs during glycolysis, pyruvate oxidation, and the Krebs cycle.

33. FAD functions in a similar manner to NAD+. FAD is reduced by two hydrogen atoms from the original glucose molecule to FADH2. This is done during the Krebs cycle. These reductions are energy harvesting and will transfer their free energy to ATP molecules. Reduced NAD+ and FAD move free energy from one place to another and from one molecule to another.

34. #13. As a result of glycolysis, pyruvate oxidation, and the Krebs cycle, only a small portion of the energy of glucose has been converted to ATP. In what form is the rest of the usable energy found at this stage of the process? The rest of the usable energy is stored as FADH2, and NADH. 2 FADH2 are produced during the Krebs cycle. The free energy stored in these molecules is released during chemiosmosis and ETC.