1. 1 Respiration Organisms can be classified based on how they obtain energy: Autotrophs –Able to produce their own organic molecules through photosynthesis Heterotrophs –Live on organic compounds produced by other organisms All organisms use cellular respiration to extract energy from organic molecules

2. 2 Cellular respiration Cellular respiration is a series of reactions Oxidized – loss of electrons Reduced – gain of electron Electron carriers are used in oxidation and reduction reactions Nicotinamide adenine dinucleotide (NAD) Flavin adenine dinucleotide (FAD)

3. 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Product Enzyme NAD + NAD 2e – H+H+ +H + Energy-rich molecule NAD + 1. Enzymes that use NAD + as a cofactor for oxidation reactions bind NAD + and the substrate. 2. In an oxidation–reduction reaction, 2 electrons and a proton are transferred to NAD +, forming NADH. A second proton is donated to the solution. 3. NADH diffuses away and can then donate electrons to other molecules. Reduction Oxidation H H H H H H H H

4. In overall cellular energy harvest –Dozens of redox reactions take place –Number of electron acceptors including NAD + In the end, high-energy electrons from initial chemical bonds have lost much of their energy Transferred to a final electron acceptor 4

5. 5 Aerobic respiration –Final electron receptor is oxygen (O 2 ) Anaerobic respiration –Final electron acceptor is an inorganic molecule (not O 2 ) Fermentation –Final electron acceptor is an organic molecule

6. 6 Aerobic respiration C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O GlucoseOxygen Carbon DioxideWater

7. 7 2e – Electrons from food High energy Low energy 2H + 1 / 2 O2O2 Energy released for ATP synthesis H2OH2O Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8. 8 ATP Cells use energy from ATP to drive endergonic reactions

9. 9 PEP – ADP Enzyme – ATP Adenosine Pyruvate P P P P P P P P P P Adenosine P P Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

10. 10 Oxidation of Glucose The complete oxidation of glucose proceeds in stages: 1. Glycolysis 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain & chemiosmosis

11. 11 Outer mitochondrial membrane Intermembrane space Mitochondrial matrix FAD O2O2 Inner mitochondrial membrane Electron Transport Chain Chemiosmosis ATP Synthase NAD + Glycolysis Pyruvate Glucose Pyruvate Oxidation Acetyl-CoA Krebs Cycle CO 2 ATP H2OH2O e–e– e–e– NADH CO 2 ATP NADH FADH 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+H+ e–e–

12. Respiration video

13. 13 Glycolysis Converts 1 glucose (6 carbons) to 2 pyruvate (3 carbons) 10-step biochemical pathway Occurs in the cytoplasm Net production of 2 ATP molecules 2 NADH produced by the reduction of NAD +

14. 14 NADH must be recycled For glycolysis to continue, NADH must be recycled to NAD + by either: 1. Aerobic respiration –Oxygen is available as the final electron acceptor –Produces significant amount of ATP 2. Fermentation –Occurs when oxygen is not available –Organic molecule is the final electron acceptor

15. 15 Fate of pyruvate Depends on oxygen availability. –When oxygen is present, pyruvate is oxidized to acetyl-CoA which enters the Krebs cycle Aerobic respiration –Without oxygen, pyruvate is reduced in order to oxidize NADH back to NAD + Fermentation

16. 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Without oxygen NAD + O2O2 NADH ETC in mitochondria Acetyl-CoA Ethanol NAD + CO 2 NAD + H2OH2O Lactate Pyruvate Acetaldehyde NADH With oxygen Krebs Cycle

17. 17 Pyruvate Oxidation In the presence of oxygen, pyruvate is oxidized –Occurs in the mitochondria in eukaryotes –Occurs at the plasma membrane in prokaryotes

18. 18 For each 3-carbon pyruvate molecule: –1 CO 2 –1 NADH –1 acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A Acetyl-CoA proceeds to the Krebs cycle Products of pyruvate oxidation

19. 19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Pyruvate Oxidation NADH Krebs Cycle Electron Transport Chain Chemiosmosis Pyruvate Oxidation: The Reaction NAD + CO 2 CoA Acetyl Coenzyme A Pyruvate Acetyl Coenzyme A O CH 3 C O–O– C  O     S CoA CH 3 OC   NADH

20. 20 Krebs Cycle Oxidizes the acetyl group from pyruvate Occurs in the matrix of the mitochondria

21. 21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CoA- (Acetyl-CoA) CoA 4-carbon molecule (oxaloacetate) 6-carbon molecule (citrate) NAD + NADH CO 2 5-carbon molecule NAD + NADH CO 2 4-carbon molecule ADP + P Krebs Cycle FAD FADH 2 4-carbon molecule NAD + NADH ATP Glycolysis Pyruvate Oxidation Electron Transport Chain Chemiosmosis ATP 4-carbon molecule Pyruvate from glycolysis is oxidized Krebs Cycle into an acetyl group that feeds into the Krebs cycle. The 2-C acetyl group combines with 4-C oxaloacetate to produce the 6-C compound citrate (thus this is also called the citric acid cycle). Oxidation reactions are combined with two decarboxylations to produce NADH, CO 2, and a new 4-carbon molecule. Two additional oxidations generate another NADH and an FADH 2 and regenerate the original 4-C oxaloacetate. NADH FADH 2 Krebs Cycle

22. 22 Krebs Cycle For each Acetyl-CoA entering: –Release 2 molecules of CO 2 –Reduce 3 NAD + to 3 NADH –Reduce 1 FAD (electron carrier) to FADH 2 –Produce 1 ATP –Regenerate oxaloacetate

23. 23 At this point Glucose has been oxidized to: –6 CO 2 –4 ATP –10 NADH –2 FADH 2 Released energy will be put to use to manufacture ATP These electron carriers proceed to the electron transport chain

24. 24 Electron Transport Chain (ETC) ETC is a series of membrane-bound electron carriers Embedded in the inner mitochondrial membrane

25. 25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mitochondrial matrix NADH + H + ADP + P i H2OH2O H+H+ H+H+ 2H + + 1 / 2 O2O2 Glycolysis Pyruvate Oxidation 2 Krebs Cycle ATP Electron Transport Chain Chemiosmosis NADH dehydrogenase bc 1 complex Cytochrome oxidase complex Inner mitochondrial membrane Intermembrane space a. The electron transport chain ATP synthase b. Chemiosmosis NAD + Q C e–e– FADH 2 H+H+ H+H+ H+H+ H+H+ e–e– 2 2 e–e– 2 2 ATP FAD

27. 27 Energy Yield of Respiration Theoretical energy yield –38 ATP per glucose for bacteria ~36 ATP per glucose for eukaryotes

28. 28 Chemiosmosis 2 5 2 3 615 2 2 2 5 NADH Total net ATP yield = 32 (30 in eukaryotes) ATP Krebs Cycle Pyruvate oxidation FADH 2 Glycolysis 2 Glucose Pyruvate ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29. 29 Oxidation Without O 2 1.Anaerobic respiration –Use of inorganic molecules (other than O 2 ) as final electron acceptor –Many prokaryotes use sulfur, nitrate, carbon dioxide or even inorganic metals 2.Fermentation –Use of organic molecules as final electron acceptor

30. 30 Fermentation Reduces organic molecules in order to regenerate NAD + 1. Ethanol fermentation occurs in yeast –CO 2, ethanol, and NAD + are produced 2. Lactic acid fermentation –Occurs in animal cells (especially muscles) –Electrons are transferred from NADH to pyruvate to produce lactic acid

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