CELLULAR RESPIRATION: Harvesting Chemical Energy

1. CELLULAR RESPIRATION:Harvesting Chemical Energy Chapter 9

4. CATABOLIC PATHWAYS • Complex molecules that are high in potential energy are broken down into smaller waste products that have less energy • Some of this released energy can later do work, but most is given off as heat • Two major catabolic pathways • Aerobic Respiration • Anaerobic respiration (fermentation)

5. AEROBIC RESPIRATION C6H1206 + 602 6CO2 + 6H20 + energy (ATP and heat) • Aerobic (uses oxygen) respiration • Exergonic • ΔG = -686 kcal/mole of glucose • Big picture – chop up glucose and make ATP • Transfer energy in glucose to ATP • Oxidation of glucose by oxygen

6. ATP (ADENOSINE TRIPHOSPHATE) • The last phosphate of ATP can be removed by enzymes and added to another molecule. • This turns ATP into ADP (adenosine diphosphate). • Molecules that receive a phosphate group have been phosphorylated. • This makes the molecule change shape, which allows the molecule to do work. • After the work is done, the phosphate group is released.

7. Figure 9.2 A review of how ATP drives cellular work

8. REDOX REACTIONS • Oxidation - loss of electrons • Reduction - gain of electrons • In respiration, transferring electrons releases energy to make ATP

10. An e- loses potential energy when it moves from a less electronegative atom toward a more electronegative atom. • In respiration, hydrogen’s electrons are transferred to oxygen (the fall of electrons), which liberates energy.

12. NAD+ • Hydrogen atoms are removed gradually from glucose. • They are transferred to oxygen by a coenzyme called NAD+(nicotinamideadenine dinucleotide). • Dehydrogenase enzymes remove a pair of hydrogen atoms (2 e- and 2 protons) from sugar. • Remember, protons (H+) are hydrogen cations or an H atom without its electron

13. The enzyme delivers 1 proton and 2 e- to its coenzyme NAD+ making NADH. • The remaining proton (H+)is released into surrounding solution. • The e- lose very little energy in this transfer.

14. Figure 9.4 NAD+ as an electron shuttle

15. The three metabolic stages of respiration: • Glycolysis • The Kreb’s cycle • The electron transport chain and oxidative phosphorylation

16. Figure 9.6 An overview of cellular respiration (Layer 3)

17. GLYCOLYSIS: “splitting of sugar” • Occurs in cytoplasm • Series of 10 steps, each with its own enzyme • No oxygen needed (anaerobic) • Needs 2 ATP to start process • Makes 4 ATP by substrate-level phopsphorylation (when an enzyme removes a phosphate from a substrate to make ATP) • Transfers electrons and H+ to NAD+ to make 2 NADH (to go to ETC)

18. Figure 9.7 Substrate-level phosphorylation

19. By the end, one glucose molecule will been broken in half to form two 3-carbon molecules of pyruvate. • Only if oxygen is present, puruvate moves into the Kreb’s cycle (Citric Acid Cycle) to continue aerobic respiration.

20. Figure 9.8 The energy input and output of glycolysis

21. Figure 9.9 A closer look at glycolysis: energy investment phase

22. Figure 9.9 A closer look at glycolysis: energy payoff phase

23. Pyruvate converts to acetyl CoA • Pyruvate enters mitochondria • Pyruvate loses CO2, and the resulting 2-carbon compound is oxidized making acetate. • The e- and H+ are transferred to NAD+ to make NADH (to go to ETC) • Coenzyme A (a vitamin B derivative) attaches to acetate making acetyl CoA

24. Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle

25. THE KREB’S CYCLE • Acetyl CoA combines with a 4-carbon molecule • This molecule is oxidized over a series of steps that are cyclic • e- and H+ are transferred to NAD+ and FAD+ to make 3 NADH and 1 FADH2(flavinadenine dinucleotide). • 2 molecules of CO2 are given off

26. 1 ATP is made by substrate-level phosphorylation • Only 2 carbons can go through the cycle at one time so the cycle must “turn” twice to oxidize both pyruvates. • CO2 diffuses out of cell, into blood, and is exhaled. • NADH and FADH2 take their electrons to the electron transport chain (ETC)

27. Figure 9.12 A summary of the Krebs cycle

28. Figure 9.11 A closer look at the Krebs cycle

29. ELECTRON TRANSPORT CHAIN • Made up of a chain of molecules embedded in the inner membrane of mitochondria • Mostly proteins with prosthetic groups that can easily donate and accept e- (redox) – many are cytochromes with heme groups (Fe) • NADH transfers e- to first molecule and FADH2 transfers e- to a lower molecule.

30. e- move down the chain via redox reactions • They move down the ETC because oxygen is electronegative and pulls the e- along • Oxygen captures the e- at bottom and along with 2 H+ (from solution) forming water • The energy released by falling e- causes H+ to be pumped out into intermembrane space.

31. H+ move back into mitochondria by diffusion (a proton-motive force) only through a protein called ATP synthase (oxidative phosphorylation) • These protons change ATP synthase’s shape so that it acts as an active site for Pi and ADP to make ATP. • Each NADH eventually yields ~3 ATP. • Each FADH2 eventually yields ~2 ATP.

32. Figure 9.13 Free-energy change during electron transport

33. Figure 9.14 ATP synthase, a molecular mill

34. Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis

35. SUMMARY OF AEROBIC RESPIRATION • Approximately 38 ATP’s made from one glucose • About 60% of energy from glucose is “lost” as heat • This heat helps to keep our warm body temperature

36. Figure 9.16 Review: how each molecule of glucose yields many ATP molecules during cellular respiration

37. ANAEROBIC RESPIRATION (FERMENTATION) • NO oxygen = anaerobic = no Kreb’s • Alcohol fermentation (yeast) • Pyruvate is converted to ethanol • Lactic acid fermentation (humans) • Pyruvate is converted to lactic acid • 2 ATP and 2 NAD+ are made • Makes NAD+ so glycolysis can continue – otherwise NADH has no where to go (without oxygen at bottom of ETC) and is not converted back to NAD+.

38. Figure 9.17a Fermentation

39. Figure 9.x2 Fermentation

40. Figure 9.17b Fermentation

41. Figure 9.18 Pyruvate as a key juncture in catabolism

42. Facultative anaerobes – organisms that make ATP through fermentation if no oxygen and through respiration if oxygen is present (ex. yeast and some bacteria)

43. Evolutionary Significance of Glycolysis • No oxygen required (early earth had no oxygen in atmosphere) • No mitochondria required (prokaryotes do not have) • Most common metabolic pathway

44. Versatility of Respiration • Proteins and lipids enter at different locations than glucose • Intermediates of respiration can be used to make other necessities (like amino acids) • Intermediates and products of respiration inhibit enzymes to slow respiration down.

45. Figure 9.19 The catabolism of various food molecules

46. Figure 9.20 The control of cellular respiration 

47. PHOTOSYNTHESIS Chapter 10

48. BASIC VOCABULARY • Autotrophs – producers; make their own “food” • Heterotrophs – consumers; cannot make own food

49. LEAF STRUCTURE • Stomata (stoma) – microscopic pores that allow water, carbon dioxide and oxygen to move into/out of leaf • Chloroplasts – organelle that performs photosynthesis • Found mainly in mesophyll– the tissue of the interior leaf • Contain chlorophyll (green pigment) • Stroma – dense fluid in chloroplast • Thylakoid membrane – inner membrane of chloroplast • Grana (granum) – stacks of thylakoid membrane

50. Figure 10.2 Focusing in on the location of photosynthesis in a plant