Cellular Respiration: Harvesting Energy from Glucose

1. Cellular Respiration:Harvesting Energy from Glucose

2. Cellular respiration: Purpose

3. Exergonic and endergonic reactions of metabolism… Exergonic: C6H12O6 + 6O2 6CO2 + 6H2O DG = -686 kcal/mole Cellular respiration! Provides the energy to run cell processes Endergonic: 6CO2+ 6H2O  C6H12O6 + 6O2DG = +686 kcal/mole Photosynthesis! Allows plants to make energy rich sugars from energy poor molecules

4. Summary of Cellular Respiration The 3 stages of cellular respiration… 1. Glycolysis: • occurs in the cytoplasm of the cell • results in the partial breakdown of glucose • anaerobic – no oxygen is used during glycolysis

5. Summary of Cellular Respiration 2. Krebs Cycle • occurs in the mitochondrial matrix • aerobic – although O2 is not used directly in this pathway, it will not occur unless enough is present in the cell. • main catabolic pathway of C.R.

6. Summary of Cellular Respiration 3. Electron Transport Chain • occurs along the inner mitochondrial membrane (IMM) • aerobic – O2is used during this pathway. • the main ATP producing pathway!

7. What happens during cellular respiration? The Big Picture! 1.The oxidation of food molecules (i.e. glucose) • food is broken down via oxidation-reduction reactions (Redox reactions). Reduction: Oxidation: Whenever a molecule is oxidized, another molecule picks up the electrons and becomes reduced. Stripping of high energy electrons (and H+ ions) from food molecules.

8. Just remember… LEO says GER!!!! lose electrons oxidation gain electrons reduction

9. The Big Picture (cont.) 2. Electrons stripped from food molecules are accepted by electroncarrier molecules (called NADH and FADH2). • Food molecules are being oxidized, and the electron carriers are being reduced. • Electrons stripped from food molecules have high potential energy. They are in a high energy shell!

10. Electron Carriers (The Big Picture cont.) 2 H+ + 2 high energy electrons

11. Electron carriers (The Big Picture cont.)

12. The Big Picture (cont.) 3. Electron carriers take these high energy electrons to the Electron Transport Chain. Electrons are run down an “electron slide”… The energy released from this “slide” is used to make ATP… At the end of the slide, the electrons and H+ are accepted by oxygen… …and become WATER!

13. C6H12O6 + 6O2 6CO2 + 6H2O Reduced! e- and H+ Oxidized!

15. Glycolysis ATP/NADH Ledger - 2 ATP The energy investment phase carbons Energy coupling ATP  ADP + P: exergonic Glu  Glu-6-P :endergonic

16. Glycolysis ATP/NADH Ledger -2ATP +2 NADH +2ATP The energy payoff phase Redox reactions Energy coupling

17. ATP/NADH Ledger Glycolysis -2ATP +2 NADH +2ATP +2ATP More energy coupling End-products of glycolysis are 2 pyruvate molecules

18. Summary of Glycolysis Glucose activation: Energy Input = 2 ATP Energy Harvest = 4 ATP + 2NADH

19. Final ledger for glycolysis Starting materials – one 6 carbon glucose molecule End products – two 3 carbon pyruvate molecules Don’t worry about all the intermediate molecules they are just there to illustrate what’s going on. What you need to know Final Ledger -2ATP +2ATP +2ATP +2ATP +2 NADH

20. Pyruvic acid must be chemically groomed to enter the Krebs cycle • Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetate molecule that binds to coenzyme A. This forms acetyl CoA, which enters the Krebs cycle. 1 NADH is produced here. Acetyl CoA(acetate and coenzyme A) Pyruvicacid CO2 Figure 6.10

21. The Krebs cycle completes the oxidation of glucose, creating many NADH and FADH2molecules • The Krebs cycle is a series of reactions in which enzymes strip away electrons and H+ from each acetyl CoA molecule Acetyl CoA 2 KREBSCYCLE CO2 Figure 6.11A

22. 2 carbons enter cycle Oxaloaceticacid 1 Citric acid CO2 leaves cycle 5 KREBSCYCLE 2 Malicacid 4 Alpha-ketoglutaric acid 3 CO2 leaves cycle Succinicacid Step Acetyl CoA stokesthe furnace Steps and NADH, ATP, , and CO2 are generated during redox reactions. Steps and Redox reactions generate FADH2and NADH. 1 2 3 4 5 Figure 6.11B

23. What you must know about the Krebs Cycle • Each turn requires one molecule of acetyl CoA. • Don’t forget there are 2 turns per glucose molecule • Each turn generates: • 3 NADH molecules • 1 ATP • 1 FADH2 molecule • Almost all of the energy removed frompyruvate molecules are carried by electron carrier molecules NADH and FADH2 • Reaction intermediates (citric acid, oxaloacetate, etc.) are required to keep the cycle going.

24. Electron Transport Chain Electron carriers (NADH and FADH2) take these high energy electrons to the Electron Transport Chain. Electrons are run down an “electron slide”… The energy released from this “slide” is used to make ATP… At the end of the slide, the electrons and H+ are accepted by oxygen… …and become WATER!

25. Proton (H+) gradient is built up as a result of NADH (produced by Krebs cycle reactions) feeding electrons into electron transport system. Electron Transport results in H+ ions being concentrated in the intermembrane space

26. ATP Synthase enzymes use a proton (H+) gradient to put ADP and P together forming 32 ATP

27. Energy yield from Aerobic Cellular Respiration