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How Cells Release Chemical Energy

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Presentation on theme: "How Cells Release Chemical Energy"— Presentation transcript:

1 How Cells Release Chemical Energy
Chapter 7

2 Impacts, Issues When Mitochondria Spin Their Wheels
Mitochondria are the organelles responsible for releasing the energy stored in foods In Luft’s syndrome, the mitochondria are active in oxygen consumption, but with little ATP formation to show for it In Friedreich’s ataxia, too much iron in the mitochondria causes an accumulation of free radicals that attack valuable molecules of life

3 The Impact Proper, or improper, functioning of mitochondria is the difference between health and disease

4 Overview of Energy-Releasing Pathways
Section 7.1 Overview of Energy-Releasing Pathways

5 Producing the Universal Currency of Life
All energy-releasing pathways: require characteristic starting materials yield predictable products and by-products produce ATP

6 ATP Is Universal Energy Source
Photosynthesizers get energy from the sun Animals get energy second- or third-hand from plants or other organisms Regardless, the energy is converted to the chemical bond energy of ATP

7 Making ATP Plants make ATP during photosynthesis
Cells of all organisms make ATP by breaking down carbohydrates, fats, and protein

8 Main Types of Energy-Releasing Pathways
Anaerobic pathways Evolved first Don’t require oxygen Start with glycolysis in cytoplasm Completed in cytoplasm Aerobic pathways Evolved later Require oxygen Start with glycolysis in cytoplasm Completed in mitochondria

9 Energy-Releasing Pathways

10 Overview of Aerobic Respiration
C6H O CO2 + 6H20 glucose oxygen carbon dioxide water

11 Overview of Aerobic Respiration

12 Main Pathways Start with Glycolysis
Glycolysis occurs in cytoplasm Reactions are catalyzed by enzymes Glucose 2 Pyruvate (six carbons) (three carbons)

13 p.106a

14 Three Series of Reactions Are Required for Aerobic Respiration
Glycolysis is the breakdown of glucose to pyruvate Small amounts of ATP are generated

15 Three Series of Reactions Are Required for Aerobic Respiration
The Krebs cycle degrades pyruvate to CO2 and water; NAD and FAD accept H+ ions and electrons to be carried to the electron transfer chain Small amounts of ATP are generated

16 Three Series of Reactions Are Required for Aerobic Respiration
Electron transfer phosphorylation processes the H+ ions and electrons to generate lots of ATP Oxygen is the final electron acceptor

17 The Role of Coenzymes NAD+ and FAD accept electrons and hydrogen from intermediates during the first two stages When reduced, they are NADH and FADH2 In the third stage, these coenzymes deliver the electrons and hydrogen to the transfer chain

18 Overview of Aerobic Respiration

19 The First Stage: Glycolysis
Section 7.2 The First Stage: Glycolysis

20 Glucose A simple sugar (C6H12O6) Atoms held together by covalent bonds

21 Glycolysis Occurs in Two Stages
Energy-requiring steps ATP energy activates glucose and its six-carbon derivatives

22 Glycolysis Occurs in Two Stages
Energy-releasing steps The products of the first part are split into 3-carbon pyruvate molecules ATP and NADH form

23 Energy-Requiring Steps

24 Energy-Releasing Steps
ATP PGAL NADH 2 ATP produced ENERGY - RELEASING STEPS OF GLYCOLYSIS NAD + P i 3 phosphoglycerate 2 PEP ADP 1,3 bisphosphoglycerate pyruvate to second set of reactions substrate level phosphorylation H O

25 Glycolysis in a Nutshell
Glucose is first phosphorylated in energy-requiring steps, then split to form two molecules of PGAL Enzymes remove H+ and electrons from PGAL to change NAD+ to NADH (which is used later in electron transfer PGAL is converted eventually to pyruvate By substrate-level phosphorylation, four ATP are produced

26 Substrate-level What? Substrate-level phosphorylation means that there is a direct transfer of a phosphate group from the substrate of a reaction to some other molecule – in this case, ADP Substrate is a reactant in a reaction – the substance being acted upon, for example, by an enzyme

27 Net Energy Yield from Glycolysis
Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield is 2 ATP and 2 NADH

28 Second Stage of Aerobic Respiration
Section 7.3 Second Stage of Aerobic Respiration

29 Second-Stage Reactions
Occur in the mitochondria Pyruvate is broken down to carbon dioxide More ATP is formed More coenzymes are reduced

30 Fig. 7-5b, p.112

31 Second Stage of Aerobic Respiration

32 Two Parts of Second Stage
Preparatory reactions Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide NAD+ is reduced Krebs cycle The acetyl units are oxidized to carbon dioxide NAD+ and FAD are reduced

33 Preparatory Reactions
pyruvate + coenzyme A + NAD+ acetyl-CoA + NADH + CO2 One of the carbons from pyruvate is released in CO2 Two carbons are attached to coenzyme A and continue on to the Krebs cycle

34 What Is Acetyl-CoA? A two-carbon acetyl group linked to coenzyme A CH3

35 Second Stage of Aerobic Respiration

36 =CoA KREBS CYCLE acetyl-CoA CoA oxaloacetate citrate NAD+ NADH H2O H2O
malate isocitrate O NAD+ NADH FAD FADH2 fumarate a-ketoglutarate succinyl-CoA O CoA NAD+ NADH succinate ADP + phosphate group ATP Stepped Art Fig. 7-7a, p.113

37 The Krebs Cycle Overall Reactants Overall Products Acetyl-CoA 3 NAD+
FAD ADP and Pi Overall Products Coenzyme A 2 CO2 3 NADH FADH2 ATP

38 Results of the Second Stage
All of the carbon molecules in pyruvate end up in carbon dioxide Coenzymes are reduced (they pick up electrons and hydrogen) One molecule of ATP is formed Four-carbon oxaloacetate is regenerated

39 Two pyruvates cross the inner mitochondrial membrane.
outer mitochondrial compartment 2 NADH inner mitochondrial compartment 6 NADH Krebs Cycle Eight NADH, two FADH 2, and two ATP are the payoff from the complete break-down of two pyruvates in the second-stage reactions. 2 FADH2 ATP 2 The six carbon atoms from two pyruvates diffuse out of the mitochondrion, then out of the cell, in six CO 6 CO2 Fig. 7-6, p.112

40 Coenzyme Reductions during First Two Stages
Glycolysis 2 NADH Preparatory 2 NADH reactions Krebs cycle FADH NADH Total FADH NADH

41 Third Stage of Aerobic Respiration – The Big Energy Payoff
Section 7.4 Third Stage of Aerobic Respiration – The Big Energy Payoff

42 Electron Transfer Phosphorylation
Occurs in the mitochondria Coenzymes deliver electrons to electron transfer chains Electron transfer sets up H+ ion gradients Flow of H+ down gradients powers ATP formation

43 Electron Transfer Phosphorylation
Electron transfer chains are embedded in inner mitochondrial compartment NADH and FADH2 give up electrons that they picked up in earlier stages to electron transfer chain Electrons are transferred through the chain The final electron acceptor is oxygen

44 Creating an H+ Gradient
OUTER COMPARTMENT NADH INNER COMPARTMENT

45 ATP Formation ATP INNER COMPARTMENT ADP + Pi

46 Summary of Transfers glycolysis e electron transfer phosphorylation
glucose glycolysis e electron transfer phosphorylation 2 PGAL 2 pyruvate 2 NADH 2 CO ATP 2 FADH H + 6 NADH 2 acetyl - CoA Krebs Cycle 4 CO 36 ADP + P i

47 Importance of Oxygen Electron transfer phosphorylation requires the presence of oxygen Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water

48 Summary of Energy Harvest (per molecule of glucose)
Glycolysis 2 ATP formed by substrate-level phosphorylation Krebs cycle and preparatory reactions Electron transfer phosphorylation 32 ATP formed

49 Energy Harvest from Coenzyme Reductions
What are the sources of electrons used to generate the 32 ATP in the final stage? 4 ATP - generated using electrons released during glycolysis and carried by NADH 28 ATP - generated using electrons formed during second-stage reactions and carried by NADH and FADH2

50 Energy Harvest Varies NADH formed in cytoplasm cannot enter mitochondrion It delivers electrons to mitochondrial membrane Membrane proteins shuttle electrons to NAD+ or FAD inside mitochondrion Electrons given to FAD yield less ATP than those given to NAD+

51 Energy Harvest Varies Skeletal muscle and brain cells
Liver, kidney, heart cells Electrons from first-stage reactions are delivered to NAD+ in mitochondria Total energy harvest is 38 ATP Skeletal muscle and brain cells Electrons from first-stage reactions are delivered to FAD in mitochondria Total energy harvest is 36 ATP

52 Fermentation Pathways
Section 7.5 Fermentation Pathways

53 Anaerobic Pathways Do not use oxygen
Produce less ATP than aerobic pathways Two types of fermentation pathways Alcoholic fermentation Lactate fermentation

54 Fermentation Pathways
Begin with glycolysis Do not break glucose down completely to carbon dioxide and water Yield only the 2 ATP from glycolysis Steps that follow glycolysis serve only to regenerate NAD+

55 Alcoholic Fermentation

56 Yeasts Single-celled fungi Carry out alcoholic fermentation
Saccharomyces cerevisiae Baker’s yeast Carbon dioxide makes bread dough rise Saccharomyces ellipsoideus Used to make beer and wine

57 Lactate Fermentation

58 Lactate Fermentation Carried out by certain bacteria
Electron transfer chain is in bacterial plasma membrane Final electron acceptor is compound from environment (such as nitrate), not oxygen ATP yield is low

59 Lactate Fermentation Lactobacillus and some other bacteria produce lactate This produces cheeses, yogurt, buttermilk and other dairy products Fermenters also are used to cure meats and in pickling Sauerkraut is an example Sour taste due to lactic acid (form of lactate)

60 Slow-twitch v. Fast-twitch muscles
Slow-twitch muscles make ATP only by aerobic respiration (no fermentation) Slow-twitch muscles are for light, steady, prolonged activity Slow-twitch muscles are red because they have lots of myoglobin, a pigment used to store oxygen They also have many mitochondria

61 Fast-twitch Muscles These pale (lighter colored) muscles have few mitochondria and no myoglobin Fast-twitch muscles, which are used for immediate and intense energy demands, use lactate fermentation to produce ATP It works quickly, but not for long Chickens have fast-twitch breast muscles used for quick flights (white meat) Ducks fly long distances – what color is their breast meat?

62 Alcoholic Fermentation

63 Lactate Fermentation

64 Alternative Energy Sources in the Body
Section 7.6 Alternative Energy Sources in the Body

65 The Fate of Glucose After eating, glucose is absorbed into the blood
Insulin levels rise, causing greater uptake of glucose by cells Glycolysis will follow Excess glucose is converted into glycogen Glycogen is known as “animal starch,” and is the main storage polysaccharide in animals Stored in the muscles and the liver

66 Between Meals When blood levels of glucose decline, pancreas releases glucagon, a hormone Glucagon stimulates liver cells to convert glycogen back to glucose and to release it to the blood Glycogen levels are adequate, but can be depleted in 12 hours (Muscle cells do not release their stored glycogen)

67 Energy Reserves Glycogen makes up only about 1 percent of the body’s energy reserves Proteins make up 21 percent of energy reserves Fat makes up the bulk of reserves (78 percent)

68 Energy from Fats Most stored fats are triglycerides in adipose tissue
Triglycerides are “three-tailed” fats Triglycerides are broken down to glycerol and fatty acids Glycerol is converted to PGAL, an intermediate of glycolysis Fatty acids are broken down and converted to acetyl-CoA, which enters Krebs cycle

69 glycolysis e electron transfer phosphorylation glucose 2 PGAL 2
electron transfer phosphorylation 2 PGAL 2 pyruvate 2 NADH 2 CO ATP 2 FADH H + 6 NADH 2 acetyl - CoA Krebs Cycle 4 CO 36 ADP + P i

70 Energy from Proteins Proteins are broken down to amino acids
Amino acids are broken apart Amino group is removed, ammonia forms, is converted to urea and excreted Carbon backbones can enter the Krebs cycle or its preparatory reactions

71 Reaction Sites

72 Section 7.7 Perspective on Life

73 Evolution of Metabolic Pathways
When life originated, atmosphere had little oxygen Earliest organisms used anaerobic pathways Later, cyclic pathway (simple form) of photosynthesis increased atmospheric oxygen Much more efficient cells arose that used oxygen as final acceptor in electron transfer

74 Processes Are Linked Aerobic Respiration Photosynthesis Reactants
Sugar Oxygen Products Carbon dioxide Water Photosynthesis Reactants Carbon dioxide Water Products Sugar Oxygen

75 Life Is System of Prolonging Order
Powered by energy inputs from sun, life continues onward through reproduction Following instructions in DNA, energy and materials can be organized, generation after generation With death, molecules are released and may be cycled as raw material for next generation


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