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Cellular Respiration: Harvesting Chemical Energy

Cellular Respiration: Harvesting Chemical Energy. Principles of energy conservation The process of cellular respiration Related metabolic processes 6O 2 +C 6 H 12 O 6  6H 2 O + 6CO 2 + energy. Concept 9.1. Metabolic pathways that release energy are called catabolic pathways

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Cellular Respiration: Harvesting Chemical Energy

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  1. Cellular Respiration:Harvesting Chemical Energy Principles of energy conservation The process of cellular respiration Related metabolic processes 6O2 +C6H 12O 6  6H2O + 6CO 2 + energy

  2. Concept 9.1 Metabolic pathways that release energy are called catabolic pathways - fermentation and cellular respiration Fermentation: partial degradation of sugars that occurs w/out the help of O2 Cellular respiration: O2 is consumed as a reactant along w/ the sugar - more efficient

  3. Redox Reactions • Reduction: gain of electrons • Oxidation: loss of electrons • Cellular respiration is a redox process

  4. Redox Reactions Redox reactions release energy when electrons move closer to electronegative atoms - the relocation of electrons releases the energy stored in food molecules, and this energy is used to synthesize ATP

  5. Concept 9.1 There is a transfer of one or more e- from one reactant to another; the electron transfers are called oxidation-reduction reactions or redox rxns. - the loss of e- from one substance is called oxidation - the addition of e- to another substance is called reduction

  6. Concept 9.1

  7. Concept 9.1 Electrons “fall” from organic molecules to oxygen during cellular respiration C6H12O6 + 6O2  6CO2 + 6H2O + Energy - by oxidizing glucose, cellular respiration takes energy out of storage and makes it available for ATP synthesis - carbohydrates and fats are reservoirs of electrons associated w/ hydrogen

  8. Concept 9.1 The “fall” of electrons during respiration is stepwise, via NAD+ and an electron transport chain Glucose is broken down over a series of steps that are each catalyzed by a specific enzyme Hydrogen atoms are stripped from the glucose and usually passed to NAD+. - NAD+ is reduced in the rxn.

  9. Concept 9.1 NAD+ is transformed to NADH - NADH will later be tapped to make ATP as the electrons continue their fall from NADH to oxygen Respiration uses an electron transport chain to break the fall of electrons to oxygen into several energy-releasing steps instead of one explosive rxn.

  10. Concept 9.1

  11. Concept 9.1 Electrons removed from food are shuttled by NADH to the “top” end of the chain. At the “bottom”, oxygen captures the electrons along with H+ ions to form water Food NADH  ETC  oxygen

  12. Concept 9.1 Respiration consists of three stages: - glycolysis, the Krebs cycle, electron transport chain (ETC) Glycolysis breaks down 1 glucose into 2 molecules of pyruvate - occurs in the cytosol Krebs cycle breaks down pyruvate into CO2 - occurs in the mitochondrial matrix

  13. Concept 9.1 ETC accepts electrons from the breakdown products of the first 2 stages - the energy released at each step of the chain is used to make ATP (oxidative phosphorylation); through redox rxns. oxidative phosphorylation accounts for 90% of generated ATP

  14. Concept 9.1

  15. Concept 9.1

  16. Concept 9.1

  17. Concept 9.1 Substrate-level phosphorylation: direct transfer of a phosphate to ADP by an enzyme Each molecule of glucose is degraded into carbon dioxide, water and 38 molecules of ATP

  18. Coenzymes are intermediate energy carriers • Found in all cells • Assist enzymes in energy transfer • NAD and FAD • Join with H+ and e- • Many coenzymes are vitamins

  19. Concept 9.1 Substrate-level phosphorylation: direct transfer of a phosphate to ADP by an enzyme Each molecule of glucose is degraded into carbon dioxide, water and 38 molecules of ATP

  20. Concept 9.1

  21. Cellular Respiration • Glycolysis • Krebs cycle • Electron transport chain

  22. Concept 9.1 Cellular respiration occurs in the mitochondria Organic + O2 Carbon + H2O + Energy compounds dioxide C6H12O6 + 6O2  6CO2 + 6H2O + Energy 1 glucose = -686 kcals

  23. Concept 9.2 Glycolysis means “splitting of sugar” - the 10 steps of glycolysis are broken down into two phases: energy investment and energy payoff - glucose (6C) 2 pyruvate (3C) Energy investment phase: the cell spends 2 ATP to phosphorylate the fuel molecules

  24. Concept 9.2 Energy payoff phase: 4 ATP are produced by substrate-level phosphorylation; 2 NAD+ are reduced to 2 NADH by the oxidation of food Net energy yield: 2 ATP and 2 NADH

  25. Glycolysis • Catabolic pathway • “To split sugar” • Glucose + 2ATP2 pyruvates + 4ATP + 2NADH • Occurs in cytosol • Anaerobic process • 10 step pathway

  26. Concept 9.3 If O2 is present, energy stored in NADH can be converted to ATP Upon entering the mitochondrion, each pyruvate is first converted to a molecule of acetyl CoA (2C) - another NAD+ is reduced to NADH

  27. Concept 9.3

  28. Intermediate Reaction(Oxidative Decarboxylation) • Occurs if O2 is present • 2 Pyruvate2 CO2 + 2 NADH + 2 Acetate • Attaches acetate to CoA  Acetyl CoA

  29. Krebs Cycle • In mitochondrial matrix • Oxidation of acetyl CoA to CO2 • Products include: 2 ATP + 6 NADH + 2 FAD + 4 CO2 • 8 step pathway

  30. Concept 9.3 Acetyl CoA will enter the Krebs cycle for further oxidation Krebs cycle - 8 steps, each catalyzed by a specific enzyme - Acetyl CoA (2C) enters, 2 CO2 (1C) leave, 3 NAD+ 3 NADH, 1 FAD  1 FADH2, 1 ADP  1 ATP

  31. Concept 9.4 Cristae: inner membrane folding of the mitochondria - increases surface area for more ETC’s Electrons removed from food during gycolysis/Krebs are transferred by NADH to the first molecule of the ETC

  32. The Electron Transport Chain • Embedded in the inner mitochondrial membrane • Most ETC molecules are proteins • Primary ATP generating pathway • Produces ATP via Substrate Level Phosphorylation and Chemiosmosis

  33. Concept 9.4 Most of the electron carriers in the ETC are proteins called cytochromes (cyt). The process goes downhill with oxygen being the final e- acceptor - for every 2 NADH, 1 O2 molecule is reduced into 2 molecules of water

  34. Concept 9.4 FADH2 adds its e- at a lower energy level than NADH on the ETC. -NADH = 3 ATP - FADH2 = 2 ATP ETC makes no ATP directly. It moves e- from food to oxygen breaking the energy drop to manageable amounts.

  35. Concept 9.4 Inside the inner membrane are enzymes called ATP synthase. - makes ATP from ADP and a phosphate ATP synthase uses energy from the ion gradient to synthesize ATP. - proton gradient

  36. Concept 9.4 The ETC is an energy converter that uses the exergonic flow of e- to pump H+ ions across the membrane - from the matrix to the inner membrane space. ATP synthases are the only place that are freely permeable to H+

  37. Chemiosmosis: the energy coupling mechanism • Electron flow actively transports H+ from the matrix into the intermembrane space • Flow of H+ “down the gradient” thru the ATP synthase complex generates ATP

  38. Concept 9.4 H+ gradient across a membrane couples the redox rxns. of the ETC to ATP synthesis - chemiosmosis: connection between the chemical rxn. Makes ATP and transport across a membrane

  39. Concept 9.4 Chemiosmosis is also found in the chloroplasts - ATP is generated during photosynthesis - light drives both e- flow down the ETC and H+ gradient formation

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