- 1.Chapter 9 Cellular Respiration: Harvesting Chemical Energy
2. Overview: Life Is Work
- Living cells require energy from outside sources
- Some animals, such as the giant panda, obtain energy by eating plants; others feed on organisms that eat plants
- Energy flows into an ecosystem as sunlight and leaves as heat
- Photosynthesis generates oxygen and organic molecules, which are used in cellular respiration
- Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work
4. LE 9-2 ECOSYSTEM Light energy Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O 2 CO 2+ H 2 O ATP powers most cellular work Heat energy 5. Catabolic pathways yield energy by oxidizing organic fuels
- Several processes are central to cellular respiration and related pathways
6. Catabolic Pathways and Production of ATP
- The breakdown of organic molecules is exergonic
- Fermentation is a partial degradation of sugars that occurs without oxygen
- Cellular respiration consumes oxygen and organic molecules and yields ATP
- Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:
- C 6 H 12 O 6+ 6O 2 6CO 2+ 6H 2 O + Energy (ATP + heat)
7. Redox Reactions: Oxidation and Reduction
- The transfer of electrons during chemical reactions releases energy stored in organic molecules
- This released energy is ultimately used to synthesize ATP
8. The Principle of Redox
- Chemical reactions that transfer electrons between reactants are calledoxidation-reductionreactions, orredox reactions
- In oxidation, a substance loses electrons, or is oxidized
- In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
- Oxidation is loss (of electrons)
- Reduction is gain (of electrons)
X e - +YX+Y e - becomes oxidized (loses electron) becomes reduced (gains electron) 9.
- The electrondonoris called thereducing agent
- The electronreceptoris called theoxidizing agent
- Some redox reactions do not transfer electronsbut changethe electron sharing in covalent bonds
- An example is the reaction between methane and oxygen
11. LE 9-3 Reactants becomes oxidized becomes reduced Products H Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water H C H H O O O O C O H H CH 4 2 O 2 + + + CO 2 Energy 2 H 2 O 12. Oxidation of Organic Fuel Molecules During Cellular Respiration
- During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced:
C 6 H 12 O 6+ 6O 2 6CO 2+ 6H 2 O + Energy becomes oxidized becomes reduced 13. Stepwise Energy Harvest via NAD +and the Electron Transport Chain
- In cellular respiration, glucose and other organic molecules are broken down in a series of steps
- Electrons from organic compounds are usually first transferred to NAD + , a coenzyme
- As an electron acceptor, NAD +functions as an oxidizing agent during cellular respiration
- Each NADH (the reduced form of NAD + ) represents stored energy that is tapped to synthesize ATP
14. LE 9-4 NAD + Nicotinamide (oxidized form) Dehydrogenase 2 e + 2 H + 2 e +H + NADH H + H + Nicotinamide (reduced form) +2[ H ] (from food) + 15.
- NADH passes the electrons to the electron transport chain
- Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction
- Oxygen pulls electrons down the chain in an energy-yielding tumble
- The energy yielded is used to regenerate ATP
16. LE 9-5 2 H ++ 2e 2 H (from food via NADH) Controlled release of energy for synthesis of ATP ATP ATP ATP 2 H + 2e H 2 O + 1 / 2O 2 1 / 2O 2 H 2 + 1 / 2O 2 H 2 O Explosive release of heat and light energy Cellular respiration Uncontrolled reaction Free energy,G Free energy,G Electron transport chain 17. The Stages of Cellular Respiration:A Preview
- Cellular respiration has three stages:
- Glycolysis (breaks down glucose into two molecules of pyruvate)
- The citric acid cycle (completes the breakdown of glucose)
- Oxidative phosphorylation (accounts for most of the ATP synthesis)
- The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
18. LE 9-6_1 Mitochondrion Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation 19. LE 9-6_2 Mitochondrion Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation ATP Substrate-level phosphorylation Citric acid cycle 20. LE 9-6_3 Mitochondrion Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation ATP Substrate-level phosphorylation Citric acid cycle ATP Oxidative phosphorylation Oxidative phosphorylation: electron transport and chemiosmosis Electrons carried via NADH Electrons carried via NADH and FADH 2 21.
- Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
- A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation
22. LE 9-7 Enzyme ADP P Substrate Product Enzyme ATP + 23. Glycolysis harvests energy byoxidizingglucose topyruvate
- Glycolysis(splitting of sugar) breaks down glucose into two molecules of pyruvate
- Glycolysis occurs in the cytoplasm and has two major phases:
24. LE 9-8 Energy investment phase Glucose 2 ATP used 2 ADP + 2 P 4 ADP + 4 P 4 ATP formed 2 NAD ++ 4e + 4 H + Energy payoff phase + 2 H + 2 NADH 2 Pyruvate + 2 H 2 O 2 Pyruvate + 2 H 2 O 2 ATP 2 NADH + 2 H + Glucose 4 ATP formed 2 ATP used 2 NAD+ + 4e + 4 H + Net Glycolysis Citric acid cycle Oxidative phosphorylation ATP ATP ATP 25. LE 9-9a_1 Glucose ATP ADP Hexokinase ATP ATP ATP Glycolysis Oxidation phosphorylation Citric acid cycle Glucose-6-phosphate 26. LE 9-9a_2 Glucose ATP ADP Hexokinase ATP ATP ATP Glycolysis Oxidation phosphorylation Citric acid cycle Glucose-6-phosphate Phosphoglucoisomerase Phosphofructokinase Fructose-6-phosphate ATP ADP Fructose- 1, 6-bisphosphate Aldolase Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate 27. LE 9-9b_1 2 NAD + Triose phosphate dehydrogenase + 2 H + NADH 2 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase Phosphoglyceromutase 2-Phosphoglycerate 3-Phosphoglycerate 28. LE 9-9b_2 2 NAD + Triose phosphate dehydrogenase + 2 H + NADH 2 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase Phosphoglyceromutase 2-Phosphoglycerate 3-Phosphoglycerate 2 ADP 2 ATP Pyruvate kinase 2 H 2 O Enolase Phosphoenolpyruvate Pyruvate The thing to remember about all of these reactions is that in a series of well-controlled chemical reactionsGlucoseis converted toPyruvate 29. 30. 31.
- Glycolysis uses glucose (6C) to produce two molecules of pyruvate (3C)
- The first step of glycolysis involves phosphorylation
- ATP is used to add a phosphate group to glucose.
- This is followed by a second phosphorylation reaction (ATP) to produce hexose biphosphate
- The hexose biphosphate is still contains 6 carbons. It is now split to to form two triose phosphate molecules (3C) each (glyceraldehyde)
- The next step is a combined oxidation-phosphorylation reaction. The enzyme first oxidizes the triose phosphate (glyceraldehyde ) into a differentcompound- glycerate
- After the oxidation reaction, the enzyme will attach an inorganic phosphate from the cytoplasm to the triose phosphate to form a triose biphosphate. This reaction does not involve ATP.
- Finally, each triose biphosphate gives up one of its phosphate groups.
- This phosphate group is taken up by ADP to form ATP. This occurs once more in the last step of glycolysis, again forming one ATP but also producing pyruvate.
- This process is summarizedby the following equation:
33. 34. The citric acid cycle completes the energy-yielding oxidation of organic molecules
- Before the citric acid cycle can begin,pyruvatemust be converted toacetyl CoA , which links the cycle toglycolysis
35. LE 9-10 CYTOSOL Pyruvate NAD + MITOCHONDRION Transport protein NADH + H + Coenzyme A CO 2 Acetyl Co A 36.
- The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix
- The cycle oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH 2per turn
37. LE 9-11 Pyruvate (from glycolysis, 2 molecules per glucose) ATP ATP ATP Glycolysis Oxidation phosphorylation Citric acid cycle NAD + NADH + H + CO 2 CoA Acetyl CoA CoA CoA Citric acid cycle CO 2 2 3 NAD + + 3 H + NADH 3 ATP ADP + P i FADH 2 FAD 38.
- The citric acid cycle has eight steps, each catalyzed by a specific enzyme
- The acetyl group of acetyl CoA joins the cycle by combining with