CHAPTER 6 How Cells Harvest Chemical Energy

1. CHAPTER 6How Cells Harvest Chemical Energy

2. How is a Marathoner Different from a Sprinter? • Long-distance runners have many slow fibers in their muscles • Slow fibers break down glucose for ATP production aerobically (using oxygen) • These muscle cells can sustain repeated, long contractions

3. Fast fibers make ATP without oxygen—anaerobically • They can contract quickly and supply energy for short bursts of intense activity • Sprinters have more fast muscle fibers

4. Leg muscles support sustained activity • The white meat consists of fast fibers • Wing muscles allow for quick bursts of flight • The dark meat of a cooked turkey is an example of slow fiber muscle

5. Without Oxygen (Anaerobic) Fermentation occurs when cells do not have oxygen. The electron transport chain is stopped. Glycolysis is the only ATP producing mechanism. Lactic Acid and Alcoholic fermentation.

6. INTRODUCTION TO CELLULAR RESPIRATION • Nearly all the cells in our body break down sugars for ATP production • Most cells of most organisms harvest energy aerobically, like slow muscle fibers • The aerobic harvesting of energy from sugar is called cellular respiration • Cellular respiration yields CO2, H2O, and a large amount of ATP

7. 6.1 Breathing supplies oxygen to our cells and removes carbon dioxide • Breathing and cellular respiration are closely related BREATHING O2 CO2 Lungs CO2 Bloodstream O2 Muscle cells carrying out CELLULAR RESPIRATION Sugar + O2 ATP + CO2 + H2O Figure 6.1

8. 6.2 Cellular respiration banks energy in ATP molecules • Cellular respiration breaks down glucose molecules and banks their energy in ATP • The process uses O2 and releases CO2 and H2O Glucose Oxygen gas Carbon dioxide Water Energy Figure 6.2A

9. The efficiency of cellular respiration (and comparison with an auto engine) Energy released from glucose banked in ATP Energy released from glucose (as heat and light) Gasoline energy converted to movement 100% About 40% 25% Burning gasolinein an auto engine Burning glucose in an experiment “Burning” glucosein cellular respiration Figure 6.2B

10. 6.3 Connection: The human body uses energy from ATP for all its activities • ATP powers almost all cell and body activities Table 6.3

11. BASIC MECHANISMS OF ENERGY RELEASE AND STORAGE 6.4 Cells tap energy from electrons transferred from organic fuels to oxygen • Glucose gives up energy as it is oxidized Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Figure 6.4

12. 6.5 Hydrogen carriers such as NAD+ shuttle electrons in redox reactions • Enzymes remove electrons from glucose molecules and transfer them to a coenzyme OXIDATION Dehydrogenaseand NAD+ REDUCTION Figure 6.5

13. 6.6 Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen • NADH delivers electrons to a series of electron carriers in an electron transport chain • As electrons move from carrier to carrier, their energy is released in small quantities Energy released and nowavailable for making ATP ELECTRON CARRIERSof the electron transport chain Electron flow Figure 6.6

14. Energy released as heat and light • In an explosion, 02 is reduced in one step Figure 6.6B

15. 6.7 Two mechanisms generate ATP High H+concentration ATP synthase uses gradient energy to make ATP • Cells use the energy released by “falling” electrons to pump H+ ions across a membrane • The energy of the gradient is harnessed to make ATP by the process of chemiosmosis Membrane Electron transport chain ATPsynthase Energy from Low H+concentration Figure 6.7A

16. Chemiosmosis NAD+ H+ : NADH

17. Chemiosmosis : H+

18. Chemiosmosis H+ NAD+ H+ : NADH

19. H+ H+ H+ H+ Chemiosmosis H+ H+ H+ H+ : H+

20. H+ H+ H+ H+ Chemiosmosis H+ H+ H+ H+ : ATP ADP P

21. H+ H+ H+ Chemiosmosis H+ H+ H+ : O ATP H+ H+

22. H+ H+ H+ Chemiosmosis H+ H+ H+ H2O ATP

23. Enzyme • ATP can also be made by transferring phosphate groups from organic molecules to ADP Adenosine Organic molecule(substrate) • This process is called substrate-level phosphorylation Adenosine New organic molecule(product) Figure 6.7B

24. STAGES OF CELLULAR RESPIRATION AND FERMENTATION 6.8 Overview: Respiration occurs in three main stages • Cellular respiration oxidizes sugar and produces ATP in three main stages • Glycolysis occurs in the cytoplasm • The Krebs cycle and the electron transport chain occur in the mitochondria

25. High-energy electrons carried by NADH • An overview of cellular respiration GLYCOLYSIS ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS KREBSCYCLE Glucose Pyruvicacid Cytoplasmicfluid Mitochondrion 2 2 32 Figure 6.8

26. 6.9 Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid Glucose Pyruvicacid Figure 6.9A

27. PREPARATORYPHASE(energy investment) Steps – A fuelmolecule is energized,using ATP. Glucose 1 3 Step 1 Glucose-6-phosphate 2 Fructose-6-phosphate 3 Fructose-1,6-diphosphate • Details of glycolysis Step A six-carbonintermediate splits into two three-carbon intermediates. 4 4 Glyceraldehyde-3-phosphate (G3P) ENERGY PAYOFF PHASE 5 Step A redoxreaction generatesNADH. 5 1,3-Diphosphoglyceric acid(2 molecules) 6 Steps – ATPand pyruvic acidare produced. 3-Phosphoglyceric acid(2 molecules) 6 9 7 2-Phosphoglyceric acid(2 molecules) 8 2-Phosphoglyceric acid(2 molecules) 9 Pyruvic acid (2 moleculesper glucose molecule) Figure 6.9B

28. 6.10 Pyruvic acid is chemically groomed for the Krebs cycle • Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle Pyruvicacid Acetyl CoA(acetyl coenzyme A) CO2 Figure 6.10

29. 6.11 The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules Acetyl CoA • The Krebs cycle is a series of reactions in which enzymes strip away electrons and H+ from each acetyl group 2 KREBSCYCLE CO2 Figure 6.11A

30. 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 generatedduring redox reactions. Steps and Redox reactions generate FADH2and NADH. 1 2 3 4 5 Figure 6.11B

31. 6.12 Chemiosmosis powers most ATP production • The electrons from NADH and FADH2 travel down the electron transport chain to oxygen • Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes • In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP

32. Proteincomplex • Chemiosmosis in the mitochondrion Intermembranespace Electroncarrier Innermitochondrialmembrane Electronflow Mitochondrialmatrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.12

33. 6.13 Connection: Certain poisons interrupt critical events in cellular respiration Rotenone Oligomycin Cyanide,carbon monoxide ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.13

34. 6.14 Review: Each molecule of glucose yields many molecules of ATP • For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules Cytoplasmic fluid Mitochondrion Electron shuttleacrossmembranes KREBSCYCLE GLYCOLYSIS 2AcetylCoA KREBSCYCLE ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS 2Pyruvicacid Glucose 32 ATP by substrate-levelphosphorylation used for shuttling electronsfrom NADH made in glycolysis by substrate-levelphosphorylation by chemiosmoticphosphorylation Maximum per glucose: 36 ATP Figure 6.14

35. 6.15 Fermentation is an anaerobic alternative to aerobic respiration • Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP • But a cell must have a way of replenishing NAD+

36. This recycles NAD+ to keep glycolysis working • In alcoholic fermentation, pyruvic acid is converted to CO2 and ethanol released GLYCOLYSIS 2 Pyruvicacid 2 Ethanol Glucose Figure 6.15A Figure 6.15C

37. As in alcoholic fermentation, NAD+ is recycled • Lactic acid fermentation is used to make cheese and yogurt • In lactic acid fermentation, pyruvic acid is converted to lactic acid GLYCOLYSIS 2 Pyruvicacid 2 Lactic acid Glucose Figure 6.15B

38. Cellular Respiration • Cellular Respiration – releases energy from the bonds of organic molecules • C6H12O6 + O2 H2O + CO2 + Energy 3 Stages Glycolysis Kreb’s (Citric Acid Cycle) Electron Transport Chain

39. Glycolysis • Glycolysis – sugar breakdown • Glucose is split into 2 pyruvate molecules • 2 net ATP are produced (-2 +4 = 2) • 2 NADH are also produced

40. Kreb’s Cycle • Oxidation of Acetyl CoA • Each glucose (2 pyruvates) yields 2 ATP 6 NADH 2 FADH2

41. Electron Transport Chain and Chemiosmosis • The electron transport chain is the part of respiration that produces the most ATP and requires oxygen. • The electrons that are carried in NADH and FADH2 molecules are used to produce ATP through Chemiosmosis.

42. Net Yield of Cellular Respiration Glycolysis – 2 ATP Krebs Cycle – 2 ATP Electron Transport – 32 ATP Each glucose yields 36 ATP

43. Glycolysis (fermentation); ETC • Watch utube video #34(ATP& respiration cc), **see iPad: photo**