Lecture 9 Cellular Respiration NSCC BIOL211

Transcription

1 Lecture 9 Cellular Respiration NSCC BIOL211 1

2 First watch this video. Seriously. NSCC BIOL211 2

3 Cellular respiration Redox reactions Glycolysis Pyruvate oxidation In this lecture Krebs Cycle Electron Transport Chain NSCC BIOL211 3

4 Why do we do respiration? Cellular respiration provides most of our ATP The components of our diet provides the reactants for cellular respiration Glucose is what we ll study today Lipids and protein breakdown will be briefly covered, and studied more in depth in another course NSCC BIOL211 4

5 Biochemical pathways are: Exergonic and endergonic reactions Oxidation and reduction reactions Enzymatic reactions NSCC BIOL211 5

6 The Big Picture NSCC BIOL211 6

7 From food to ATP Amylase in saliva starts to break down starches to disaccharides Stomach acid breaks apart large structures such as cells and intercellular structures Amylase in the small intestine completes the breakdown of all carbohydrates to disaccharides Maltases, lactases, and sucrases break down disaccharides into monosaccharides Glucose is brought to all the cells in the body through the circulatory system NSCC BIOL211 7

8 Energy production sites in the cell Glucose is brought inside the cell by cotransport with sodium The mitochondria are where ATP is produced NSCC BIOL211 8

9 Electron energy levels An electron loses potential energy when it shifts to a more electronegative atom C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy Here, electrons are transferred from carbon and hydrogen to oxygen The electrons in this reaction lose a LOT of potential energy Carbohydrates and fats are high-energy foods because they have a lot of electrons associated with hydrogen NSCC BIOL211 9

10 Free energy, G Figure 9.5 Free energy, G H 2 1 / 2 O 2 2 H (from food via NADH) Controlled release of 2 H + 2 e energy for synthesis of ATP ATP 1 / 2 O 2 Explosive release of heat and light energy ATP ATP 2 e 2 H + 1 / 2 O 2 H 2 O H 2 O (a) Uncontrolled reaction (b) Cellular respiration NSCC BIOL211 10

11 The chemical reactions in respiration The chemistry definition: Oxidation and reduction OIL RIG Oxidation is losing Reduction is gaining Oxygen is highly electronegative What is being lost and gained? Electrons! Electrons are usually lost to oxygen Oxidation and reduction reactions often occur in a pair, and together are called redox reactions NSCC BIOL211 11

12 The chemical reactions in respiration The biology definition: Oxidation and reduction Losing a hydrogen atom Gaining a hydrogen atom In biochemical reactions, hydrogen is what usually gets swapped around Hydrogen almost always bonds to an atom that is more electronegative (C, O, N, P), and so loses its electron NSCC BIOL211 12

13 Redox Reactions NSCC BIOL211 13

14 The chemical reactions in respiration Redox reactions Phosphorylation/dephosphorylation Carried out by kinases and phosphatases Phosphorylation increases chemical potential energy and primes the molecule for work NSCC BIOL211 14

15 New players in the enzyme game NAD + and NADH FAD and FADH 2 NAD + is derived from niacin NAD + is a coenzyme FAD is derived from riboflavin NAD+ shuttles electrons through the various stages of cellular respiration NSCC BIOL211 15

16 NAD + and FAD NAD + reduction NADH Reduced form Oxidized form oxidation NAD+ accepts electrons and becomes NADH NAD+ is reduced into NADH NADH is a reducing agent, and is recycled back to NAD + through oxidation Each NADH (the reduced form of NAD + ) represents stored energy that is tapped to synthesize ATP. Each NADH produces 3 ATPs in the e- transport chain NSCC BIOL211 16

17 What is cellular respiration? Glucose Energy - 686kcal/mol C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy Cellular respiration 1 molecule of glucose produces 28 ATPs 38 ATP Heat Cellular respiration is the step-by-step release and harness of the chemical potential energy in glucose NSCC BIOL211 17

18 Redox Reactions in Cellular Respiration During cellular respiration, the fuel (such as glucose) is oxidized, and O 2 is reduced becomes oxidized becomes reduced NSCC BIOL211 18

19 Two types of cellular respiration: The breakdown of organic molecules is always exergonic Aerobic respiration takes place in the presence of oxygen Anaerobic respiration takes place in the absence of oxygen Fermentation is a type of anaerobic respiration where sugars are partially degraded Consumes compounds other than oxygen Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration NSCC BIOL211 19

20 NSCC BIOL211 20

21 The stages of aerobic respiration Breaks glucose in half Glycolysis Consumes two ATP Generates 4 ATP Net 2 ATP Rearranges the halfglucose molecule Citric Acid Cycle* Generates 2 ATP Electrons from glucose are passed around Electron Transport Chain Generates 34 ATP *AKA the Krebs cycle and the TCA cycle NSCC BIOL211 21

22 The Big Picture NSCC BIOL211 22

23 Figure Glycolysis Electrons carried via NADH Glycolysis Glucose Pyruvate CYTOSOL MITOCHONDRION ATP Substrate-level phosphorylation NSCC BIOL211 23

24 Glycolysis The players: Glucose Pyruvate ADP/ATP Enzymes The processes: Substrate-level phosphorylation The locations Cytoplasm The production of ATP from ADP by direct transfer of a phosphate group from a phosphorylated protein NSCC BIOL211 24

25 Glycolysis Beginning structure: End structures: - Breaking down of glucose - Can be done with or without oxygen glyco = glucose lysis = breaking Broken down into two stages: The investment phase (uses 2 ATP) The payoff phase (produces 2 ATP) apart You have to spend money to make money NSCC BIOL211 25

26 Glycolysis NSCC BIOL211 26

27 Glycolysis NSCC BIOL211 27

28 Glycolysis NSCC BIOL211 28

29 Glycolysis NSCC BIOL211 29

30 Glycolysis NSCC BIOL211 30

31 Glycolysis NSCC BIOL211 31

32 Glycolysis NSCC BIOL211 32

33 Glycolysis NSCC BIOL211 33

34 Glycolysis NSCC BIOL211 34

35 Glycolysis NSCC BIOL211 35

36 Glycolysis Begin: Glucose NAD + ADP End: 2 pyruvate 2 NADH 2 ATP Most of glycose s original energy is still present in pyruvate! NSCC BIOL211 36

37 Glycolysis In the presence of O 2, pyruvate enters the mitochondrion where the oxidation of glucose is completed during TCA cycle Without O 2, pyruvate undergoes fermentation into either ethanol or lactic acid NSCC BIOL211 37

38 Glycolysis NSCC BIOL211 38

39 Pyruvate Oxidation Glycolysis feeds into TCA cycle ONLY when oxygen is present!! NSCC BIOL211 39

40 Pyruvate Oxidation Before pyruvate can be fed into TCA cycle, it must become acetyl-coa (acetyl-coenzyme A) It does this through pyruvate oxidation Produces one NADH from NAD+ Three-carbon pyruvate is converted into twocarbons + acetyl-coa Think of acetyl- CoA as a transporter for the carbon atoms from pyruvate NSCC BIOL211 40

41 Pyruvate Oxidation NSCC BIOL211 41

42 Pyruvate Oxidation Acetyl-CoA couples with oxaloacetate, the first molecule in TCA cycle Acetyl-CoA + oxaloacetate = citrate NSCC BIOL211 42

43 The Citric Acid Cycle The players: Acetyl-CoA Oxaloacetate Plus many more carbon skeleton intermediates Enzymes The processes: Hydrolysis Redox reactions The locations: Mitochondrial matrix NSCC BIOL211 43

44 The Citric Acid Cycle Begin: Oxaloacetate 1 ADP 3 NAD+ 1 FAD End: Oxaloacetate 1 ATP 3 NADH 1 FADH 2 The citric acid cycle, also called the Krebs cycle, completes the break down of pyruvate to CO 2 The citric acid cycle has eight steps, each catalyzed by a specific enzyme NSCC BIOL211 44

45 The Citric Acid Cycle NSCC BIOL211 45

46 The Citric Acid Cycle Step 1 and 2: Overview NSCC BIOL211 46

47 The Citric Acid Cycle Step 1 and 2: In detail CoA is recycled here to go back to pyruvate oxidation NSCC BIOL211 47

48 The Citric Acid Cycle Step 3 and 4: In detail and overview NSCC BIOL211 48

49 The Citric Acid Cycle Step 5 and 6: Overview NSCC BIOL211 49

50 The Citric Acid Cycle Step 5 and 6: In detail NSCC BIOL211 50

51 The Citric Acid Cycle Step 7 and 8: Overview NSCC BIOL211 51

52 The Citric Acid Cycle Step 7 and 8: In detail NSCC BIOL211 52

53 The Citric Acid Cycle The citric acid cycle is the entry point for other catabolic pathways Acetyl-CoA can be derived from carbohydrates, proteins, and fats NSCC BIOL211 53

54 The Citric Acid Cycle This is for one pyruvate. Remember, one glucose molecule produces two pyruvates! Begin: Acetyl-CoA Oxaloacetate 3NAD+ 2 FAD 1ADP The whole point of TCA cycle is to produce NADH and FADH 2 End: 3 CO 2 s Oxaloacetate 3 NADH 2 FADH 2 1 ATP NSCC BIOL211 54

55 The Citric Acid Cycle NSCC BIOL211 55

56 The electron transport chain The whole cellular process is about producing ATP. Why do we care about NADH and FADH 2? These molecules then get oxidized in the electron transport chain Every NADH will produce 3 ATP Every FADH 2 will produce 2 ATP NSCC BIOL211 56

57 The electron transport chain Begin: ADP 10 NADH 2 FADH 2 End: ATP 10 NAD+ 2 FAD Electrons are passed along at lower and lower energy levels to release their energy The electron transport chain breaks the large free-energy drop from food to O 2 into smaller steps that release energy in manageable amounts NSCC BIOL211 57

58 The electron transport chain The players: FADH 2, NADH, ADP ATP Synthase Cytochromes and membrane proteins The processes: Chemiosmosis The location: Intermembrane space of the mitochondria NSCC BIOL211 58

59 The electron transport chain The electron transport chain is a series of proteins that pass along electrons Electrons come from NADH and FADH 2 Proteins are embedded in the matrix membrane Each time an electron is passed, it releases energy That energy is used to drive protons across the membrane into the intermembrane space This creates an electrochemical gradient NSCC BIOL211 59

60 Energy increases The electron transport chain NADH NAD + + H + + 2e - CoQ Release of energy CoQ, CytC, and CytB are all membrane proteins on the inner matrix membrane CytC Release of energy CytB Release of energy O 2 NSCC BIOL211 60

61 The electron transport chain FADH 2 s electrons are lower energy than NADH, and so enter the electron transport chain at a protein further along in the chain The transport proteins alternate reduced and oxidized states as they accept and donate electrons Oxygen accepts those now very-low energy electrons. Oxygen is the terminal electron acceptor NSCC BIOL211 61

62 The electron transport chain The release of energy is used to pump H+ across the matrix membrane into the intermembrane space NSCC BIOL211 62

63 The electron transport chain H+ are pumped against their gradient using the energy released from passing electrons to lower and lower energy states This creates an electrochemical gradient We can then couple the potential energy in the electrochemical gradient to another biochemical reaction NSCC BIOL211 63

64 The electron transport chain A bigger picture: NSCC BIOL211 64

65 The electron transport chain What is that electrochemical gradient used for? To create ATP! How is that done? Through a protein called ATP synthase ATP synthase translates the potential energy in the electrochemical gradient into the potential energy in the phosphate bonds of ATP The flow of H+ with its electrochemical gradient is an exergonic reaction ATP synthase couples an exergonic reaction with an endergonic reaction NSCC BIOL211 65

66 The electron transport chain ATP synthase is a turbine that connects the flow of protons to ADP ATP phosphorylation This is called chemiosmosis Electrochemical energy Kinetic energy Chemical energy NSCC BIOL211 66

67 The electron transport chain As the turbine turns with the current of protons flowing past, it phosphorylates ADP into ATP NSCC BIOL211 67

68 The electron transport chain ATP Synthase: another view NSCC BIOL211 68

69 The electron transport chain All together: NSCC BIOL211 69

70 The electron transport chain The energy stored in a H + gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis The H + gradient is referred to as a proton-motive force, emphasizing its capacity to do work NSCC BIOL211 70

71 Energy flows in this direction: glucose NADH electron transport chain proton-motive force ATP NSCC BIOL211 71

72 What happens without oxygen? NSCC BIOL211 72

73 Fermentation Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O 2, for example sulfate Produces much less energy than aerobic respiration Only source of ATP is substrate-level phosphorylation NSCC BIOL211 73

74 Fermentation Two common types of fermentation: Lactic acid fermentation Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O 2 is scarce Alcohol fermentation Alcohol fermentation by yeast is used in brewing, winemaking, and baking NSCC BIOL211 74

75 Alcohol Fermentation Pyruvate is converted to ethanol in two steps NADH produced in glycolysis is oxidized to NAD+ Glucose is not conpletely digested NSCC BIOL211 75

76 Lactic Acid Fermentation Pyruvate is converted to lactate in one step NADH produced during glycolysis is oxidized to NAD+ NSCC BIOL211 76

77 Comparing Aerobic and Anaerobic Respiration Aerobic Respiration Glycolysis Yes Yes Krebs Cycle Yes No Electron Transport Chain Yes Anaerobic Respiration ATP Production 32 per glucose 2 per glucose No NADH production Yes Yes FADH 2 production Yes No Terminal electron acceptor O 2 Pyruvate or acetaldehyde NSCC BIOL211 77

78 Who uses what pathway? Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O 2 Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration We require oxygen to live, and are obligate aerobes In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes NSCC BIOL211 78

79 Figure 9.18 Glucose CYTOSOL Glycolysis Pyruvate No O 2 present: Fermentation O 2 present: Aerobic cellular respiration Ethanol, lactate, or other products Acetyl CoA MITOCHONDRION Citric acid cycle

80 Catabolism of other biomolecules Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) Fatty acids are broken down by beta oxidation and yield acetyl CoA An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate NSCC BIOL211 80

81 Controlling Respiration ATP and citrate inhibit phosphofructokinase AMP is a positive allosteric regulator of phosphofructokinase If you have a lot of ATP or citrate (that means a lot of energy) glycolysis is shut down If you have a lot of AMP (very little energy is present) glycolysis is stimulated If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down NSCC BIOL211 81

82 The Evolutionary Significance of Glycolysis Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere Very little O 2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP Glycolysis is a very ancient process NSCC BIOL211 82

83 Vocabulary Glycolysis Krebs/TCA cycle Redox reactions Terminal electron acceptor Chemiosmosis Oxidative phosphorylation Proton-motive force Fermentation NSCC BIOL211 83