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Chapter 9

Chapter 9. Cellular Respiration: Harvesting Chemical Energy. Respiration Facts:. All the energy in all the food you eat can be traced back to sunlight If you exercise too hard, your muscles shut down from a lack of oxygen. FEELING THE “ BURN ”. When you exercise:

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Chapter 9

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  1. Chapter 9 Cellular Respiration: Harvesting Chemical Energy

  2. Respiration Facts: • All the energy in all the food you eat can be traced back to sunlight • If you exercise too hard, your muscles shut down from a lack of oxygen

  3. FEELING THE “BURN” When you exercise: • Muscles need energy in order to perform work • Your cells use oxygen to release energy from the sugar glucose • Both aerobic and anaerobic burning of glucose can take place in your cells

  4. Aerobic & Anaerobic Metabolism • Aerobic metabolism - When enough oxygen reaches cells to support energy needs - Maximum energy production • Anaerobic metabolism • When the demand for oxygen outstrips the body’s ability to deliver it • Low energy production

  5. Anaerobic Metabolism • Without enough oxygen, muscle cells break down glucose to produce lactic acid • Lactic acid is associated with the “burn” associated with heavy exercise • If too much lactic acid builds up, your muscles give out

  6. Physical Conditioning • Allows your body to adapt to increased activity • The body can increase its ability to deliver oxygen to muscles • Long-distance runners wait until the final sprint to exceed their aerobic capacity

  7. Why Photosynthesis? • Only producersare capable of Photosynthesis • Light energy from the sun powers this chemical process that makes organic molecules (sugars) • This process occurs in the mesophyll cells of leaves of producers (plants & algae)

  8. ENERGY FLOW IN THE BIOSPHERE Energy stored in food can be traced back to the sun Fuel molecules in food store solar energy in chemical bonds Animals depend on plants to convert solar energy to chemical energy This chemical energy is in the form of sugars and other organic molecules

  9. Autotrophs & Heterotrophs • Autotrophs - Plants and other organisms that make all their own organic matter from inorganic nutrients • Heterotrophs - Humans and other animals that cannot make organic molecules from inorganic ones

  10. The Cycle of Energy • Producers - Biologists refer to plants and other autotrophs as the producers in an ecosystem • Consumers - Heterotrophs are consumers, because they eat plants or other animals

  11. Chemical Cycling • The ingredients for photosynthesis are carbon dioxide and water • CO2 is obtained from the air by a plant’s leaves • H2O is obtained from the damp soil by a plant’s roots • Chloroplasts rearrange the atoms of these ingredients to produce sugars (glucose) and other organic molecules • Oxygen gas is a by-product of photosynthesis

  12. Chemical Cycling • Both plants and animals perform cellular respiration • Cellular respiration is a chemical process that harvests energy from organic molecules and occurs in the mitochondria • The waste products of cellular respiration, CO2 and H2O, are used in photosynthesis

  13. Sunlight supplies the energy! Sunlight energy Bonds of Glucose, made in chloroplasts, contain the stored energy Ecosystem Photosynthesis (in chloroplasts) Raw materials for cellular respiration Carbon dioxide Raw materials for photosynthesis Glucose Oxygen Water Glucose broken down to release energy for cellular work Cellular respiration (in mitochondria) Cellular energy Heat energy

  14. AEROBIC HARVEST OF FOOD ENERGY • Cellular respiration is the main way that chemical energy is harvested from food and converted to ATP for cellular work • Cellular respiration is an aerobic process requiring oxygen

  15. The Versatility of Cellular Respiration Cellular respiration can “burn” other kinds of molecules besides glucose: Diverse types of carbohydrates Fats Proteins 15

  16. The Overall Equation for Cellular Respiration • A common fuel molecule for cellular respiration is glucose • This is the overall equation for what happens to glucose during cellular respiration Glucose Oxygen Carbon dioxide Water Energy

  17. But Remember … • Cellular Respiration is a metabolic pathway, not a single reaction • Many chemical reactions, both aerobic and anaerobic, are involved in the process of cellular respiration • Lots of enzymes are required for the process to occur

  18. The Relationship Between Cellular Respiration and Breathing • Cellular respiration and breathing are closely related • Cellular respiration requires a cell to exchange gases with its surroundings • Breathing exchanges these gases between the blood and outside air

  19. Breathing Lungs Muscle cells Cellular Respiration

  20. The Role of Oxygen in Cellular Respiration • During cellular respiration, hydrogen and its bonding electrons change partners • Hydrogen and its electrons go from sugar to oxygen, forming water

  21. Redox Reactions • Chemical reactions that transfer electrons from one substance to another are called oxidation-reduction reactions • REDOX short for oxidation-reduction reactions

  22. Redox Reactions • The loss of electrons during a redox reaction is called oxidation • The acceptance of electrons during a redox reaction is called reduction • Reducing agent: e- donor • Oxidizing agent: e- acceptor

  23. REDOX in Cellular Respiration Glucose loses electrons (and hydrogens) Oxidation Oxygen Glucose Carbon dioxide Water Reduction Oxygen gains electrons (and hydrogens)]

  24. Comparison

  25. The Metabolic Pathway of Cellular Respiration • Cellular respiration is an example of a metabolic pathway • A series of chemical reactions in cells either building or breaking down molecules

  26. The Metabolic Pathway of Cellular Respiration All of the reactions involved in cellular respiration can be grouped into three main stages • Glycolysis – occurs in cytoplasm • The Krebs cycle – occurs in matrix of mitochondria • Electron transport – occurs across the mitochondrial membrane

  27. A Road Map for Cellular Respiration Mitochondrion Cytosol High-energy electrons carried mainly by NADH High-energy electrons carried by NADH Glycolysis Krebs Cycle 2 Pyruvic acid Electron Transport Glucose

  28. Glycolysis Stage One

  29. Stage 1: Glycolysis • Glycolysis takes place in the cytoplasm • Oxygen NOT required • Process breaks a six-carbon glucose into two, three-carbon molecules • A molecule of glucose is split into two molecules of pyruvic acid • These molecules then donate high energy electrons to NAD+, forming NADH

  30. Glycolysis METABOLIC PATHWAY 2 Pyruvic acid Glucose

  31. Glycolysis CoA Acetic acid Pyruvic acid Acetyl-CoA (acetyl-coenzyme A) CO2 Coenzyme A 31

  32. The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2 The cycle uses some of this energy to make ATP The cycle also forms NADH and FADH2( 2 energy carrier molecules) Glycolysis Summary 32

  33. Krebs Cycle Stage Two

  34. Stage 2: The Krebs Cycle • The Krebs cycle completes the breakdown of sugar • It occurs inside the mitochondria • In the Krebs cycle, pyruvic acid from glycolysis is first “prepped” into a usable form by combining it with enzyme Co-A to make Acetyl-CoA

  35. ACETYL Co-A Input Output 2 Acetic acid 1 2 CO2 3 ADP Krebs Cycle 3 NAD 4 FAD 5 6

  36. Electron Transport Stage 3

  37. Stage 3: Electron Transport • Electron transport releases the energy your cells need to make the most of their ATP • The molecules of electron transport chains are built into the inner membranes of mitochondria

  38. Stage 3: Electron Transport The chain functions as a chemical machine that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane These ions store potential energy

  39. Electron transport chain • Cytochromes carry electron carrier molecules (NADH & FADH2) down to oxygen • Chemiosmosis: energy coupling mechanism • ATP synthase: produces ATP by using the H+ gradient (proton-motive force) pumped into the inner membrane space from the electron transport chain; this enzyme harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation)

  40. Protein complex Electron carrier Inner mitochondrial membrane Electron flow ATP synthase Electron transport chain

  41. Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Acetyl- CoA Krebs Cycle Glycolysis Electron Transport

  42. Adding Up the ATP Cytosol Mitochondrion Glycolysis 2 Acetyl- CoA Krebs Cycle 2 Pyruvic acid Electron Transport Glucose Maximum per glucose: by ATP synthase by direct synthesis by direct synthesis Figure 6.14

  43. FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY Some of your cells can actually work for short periods without oxygen (anaerobic respiration) For example, muscle cells can produce ATP under anaerobic conditions Called Fermentation Involves The anaerobic harvest of food energy

  44. Fermentation in Human Muscle Cells • Human muscle cells can make ATP with and without oxygen • They have enough ATP to support activities such as quick sprinting for about 5 seconds • A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds • To keep running, your muscles must generate ATP by the anaerobic process of fermentation

  45. Glycolysis is the metabolic pathway that provides ATP during fermentation • Pyruvic acid is reduced by NADH, producing NAD+, which keeps glycolysis going • In human muscle cells, lactic acid is a by-product

  46. 2 ADP+ 2 Glycolysis 2 NAD 2 NAD Glucose 2 Pyruvic acid + 2 H 2 Lactic acid Lactic acid fermentation

  47. Fermentation in Microorganisms • Various types of microorganisms perform fermentation • Yeast cells carry out a slightly different type of fermentation pathway • This pathway produces CO2 and ethyl alcohol

  48. 2 ADP+ 2 2 CO2 released 2 ATP Glycolysis 2 NAD 2 NAD 2 Ethyl alcohol Glucose 2 Pyruvic acid + 2 H Alcoholic fermentation

  49. The food industry uses yeast to produce various food products

  50. Related metabolic processes • Fermentation: alcohol~ pyruvate to ethanol lactic acid~ pyruvate to lactate • Facultative anaerobes (yeast/bacteria) • Beta-oxidation lipid catabolism

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