CHAPTER 6 How Cells Harvest Chemical Energy

1. CHAPTER 6How Cells Harvest Chemical Energy Modules 6.1 – 6.7

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

6. 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

7. 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 Review: 2nd law of thermodynamics, wasted energy is lost to each system as random KE (heat).

8. 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

9. 6.3 Connection: The human body uses energy from ATP for all its activities • ATP powers almost all cell and body activities • Body maintenance • Breathing, digesting food, temperature and blood circulation • Voluntary activities require additional energy input and utilize calories at a faster rate then simple body maintenance • Total expenditure = 2200 kcal a day Table 6.3

10. 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

11. 1 glucose molecule contains more energy than a cell needs to use for a single job ** Look at equation at the bonds of reactants and products in cellular respiration • Movement of H represents electron transfer • Don’t see e-’s • CR is a series of steps, coupling exergonic with an endergonic reaction • ** Review coupling: Glucose breakdown (exergonic – energy released) -> ATP synthesis (endergonic – energy stored)

12. Some of the energy that is released is stored in the phosphate bonds of ATP • Coupling of the release of energy of ATP, an exergonic reaction, to provide energy to drive endergonic reactions • At each step, electrons move from chemical bond in a molecule where they have more energy to a bond where they have less energy. • Oxygen atoms are the ultimate (final) electron acceptors. When these oxygen atoms bind with the hydrogen atoms carrying the electrons, they form water molecules with relatively low-energy covalent bonds.

13. 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

14. Oxidation reactions involve electron loss and are exergonic half • Reduction reactions involve electron gain and are the endergonic half • LEO-GER “Loss of Electrons, Oxidation; Gain of electrons, reduction • Each step in glucose breakdown includes small redox reaction • Enzyme = dehydrogenase and coenzyme = NAD+ • Glucose oxidized, NAD+ reduced forming NADH

15. Dehydronase removes H+’s from given molecule (glucose) • NAD+ picks up a H+ to become NADH • Electron carrier • Got reduced (gained electrons) Some H+ goes into solution

16. 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 • NADH with less potential energy then glucose • Gets oxidized and NADH  back to NAD+ w/ H+’s passed down chain • ETC song • 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

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

18. Ultimate electron acceptor is oxygen • Small amounts of energy released that can build ATP • ETC • In eukaryotic cells found in mitochondrial membrane • In prokaryotic cells found in plasma membrane

19. 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 • The electron transport temporarily produces PE in the form of an increase of H+. ATP synthases use the PE to generate ATP by H+ flow through them • http://www.youtube.com/watch?v=QHmdJtiaNYg&feature=player_embedded Membrane Electron transport chain ATPsynthase Energy from Low H+concentration Figure 6.7A

20. 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 • NO membranes or ETC involved Adenosine New organic molecule(product) Figure 6.7B

21. Chemiosmosis – requires membranes (ETC) • Substrate- level – requires no membranes (Glycolysis or Krebs) • Not as efficient = less ATP made

22. Black-Eyed Peas – Cellular Respiration Song

23. STAGES OF CELLULAR RESPIRATION AND FERMENTATION 6.8 Overview: Respiration occurs in four main stages • Cellular respiration oxidizes sugar and produces ATP in three main stages • Glycolysis occurs in the cytoplasm • The Krebs cycle (matrix) and the electron transport chain (cristae) occur in the mitochondria • Chemiosmosis occurs following ETC

24. High-energy electrons carried by NADH • An overview of cellular respiration • All interconnected, all with some ATP synthesis GLYCOLYSIS ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS KREBSCYCLE Glucose Pyruvicacid Cytoplasmicfluid Mitochondrion Figure 6.8

25. 6.9 Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid Occurs in all cells, under all conditions (aerobic and anaerobic); animals, plants, fungi Glucose Pyruvicacid Figure 6.9A

26. 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 • Net result is 1 6C molecule split into 2 3C molecules • Each of 9 steps different enzme • Reactants include glucose, ADP, phosphate and NAD+ • ATP to get things started • Look at overall reactants and products 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)

27. 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 • Pyruvic acid is an intermediate or a bridge oxidized Pyruvicacid Acetyl CoA(acetyl coenzyme A) waste High-energy for Krebs CO2 Figure 6.10

28. Compare the amount of chemical energy in glucose versus the two pyruvic acid molecules • Glucose with more energy than pyruvate. Why? • Look at the number of bonds

29. How will the NADH be used to make ATP • Chemiosmosis, NADH will carry electrons to the ETC

30. 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 in the matrix strip away electrons and H+ from each acetyl group • Look at products and reactants and net energy production • What is usable now or later? Needed to restart cycle 2 KREBSCYCLE CO2 Not immediate Not immediate immediate

31. 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

32. Official first step of Krebs • Formation of citric acid • A molecule of 2-carbon CoA joined with 4-carbon oxaloacetic acid • Results in 6-carbon citric acid

33. 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

34. Proteincomplex • Chemiosmosis in the mitochondrion (inner membrane, cristae) • Net energy production = 32 ATP per glucose (only if O2 is available Intermembranespace Electroncarrier Innermitochondrialmembrane Electronflow Mitochondrialmatrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.12

35. Advantage of membranes in general as related to membrane in mitochondria • Increased surface area • Increases amount of ETC/ATP synthases

36. 6.13 Connection: Certain poisons interrupt critical events in cellular respiration Rotenone Oligomycin Cyanide,carbon monoxide ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.13

37. 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 • Review – second chance at Black-eyed Peas Cytoplasmic fluid Mitochondrion Electron shuttleacrossmembranes KREBSCYCLE GLYCOLYSIS 2AcetylCoA KREBSCYCLE ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS 2Pyruvicacid Glucose by substrate-levelphosphorylation used for shuttling electronsfrom NADH made in glycolysis by substrate-levelphosphorylation by chemiosmoticphosphorylation Maximum per glucose: Figure 6.14

38. Compare glycolysis vs. Krebs • Glycolysis • 2 ATP + 2 NADH • Krebs (based on 2 CoA molecules) • 2 ATP • 6 NADH • 2 FADH2

39. Overall review • 4 ATP from glycolysis and Krebs by substrate-level phosphorlyation • 40% glucose converted to ATP • Each NADH = 3 ATP (ETC/Chemiosmosis) • Each FADH2 = 2 ATP (ETC/Chemiosmosis) • Maximum yield per glucose is 38 ATP, but may be less due to energy used to shuttle NADH from glycolysis in cytoplasm to mitochondria

40. 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+

41. 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

42. As in alcoholic fermentation, NAD+ is recycled • Lactic acid fermentation is used to make cheese and yogurt • Responsible for muscle soreness after working out • In lactic acid fermentation, pyruvic acid is converted to lactic acid GLYCOLYSIS 2 Pyruvicacid 2 Lactic acid Glucose Figure 6.15B

43. Different types of bacteria • Strict anaerobes • Require anaerobic conditions and are poisoned by O2 • Facultative anaerobes • Can make ATP by fermentation or chemiosmosis depending on if O2 is available or not

44. INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS 6.16 Cells use many kinds of organic molecules as fuel for cellular respiration • Polysaccharides can be hydrolyzed to monosaccharides and then converted to glucose for glycolysis • Proteins can be digested to amino acids, which are chemically altered and then used in the Krebs cycle • Fats are broken up and fed into glycolysis and the Krebs cycle

45. Food, such as peanuts • Pathways of molecular breakdown Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Pyruvicacid ELECTRONTRANSPORT CHAINAND CHEMIOSMOSIS Glucose G3P AcetylCoA KREBSCYCLE GLYCOLYSIS Figure 6.16

46. Pathways (look at draw and follow arrows for each of the following) • Polysaccharides  convert to glucose, then 3 stages plus intermediate • Proteins  convert to Pyruvic acid, Acetyl CoA, or Kreb’s cycle and then continues depending on the point of entry • Fatty acids  acetyl CoA to Kreb’s • Glycerol  G3P (glycolysis intermediate)

47. Fat due to the large amount of (H+)’s result in the most ATP produced • More than starch/sugar

48. 6.17 Food molecules provide raw materials for biosynthesis • In addition to energy, cells need raw materials for growth and repair • Some are obtained directly from food • Others are made from intermediates in glycolysis and the Krebs cycle • Biosynthesis consumes ATP • Can produce molecules that are not actually present in the original food

49. ATP needed todrive biosynthesis • Biosynthesis of macromolecules from intermediates in cellular respiration GLUCOSE SYNTHESIS KREBSCYCLE AcetylCoA Pyruvicacid G3P Glucose Aminogroups Amino acids Fatty acids Glycerol Sugars Proteins Fats Polyscaccharides Cells, tissues, organisms Figure 6.17

50. 6.18 The fuel for respiration ultimately comes from photosynthesis • All organisms have the ability to harvest energy from organic molecules • Plants, but not animals, can also make these molecules from inorganic sources by the process of photosynthesis • Converts CO2 and H2O into organic compounds using light energy Figure 6.18