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Chapter 9 – Cellular Respiration

Chapter 9 – Cellular Respiration. Overview: Life Is Work Living cells Require transfusions of energy from outside sources to perform their many tasks Assemble polymers Pump substances against the membrane Move Reproduce. Cellular Respiration. Basics of Respiration.

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Chapter 9 – Cellular Respiration

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  1. Chapter 9 – Cellular Respiration • Overview: Life Is Work • Living cells • Require transfusions of energy from outside sources to perform their many tasks • Assemble polymers • Pump substances against the membrane • Move • Reproduce

  2. Cellular Respiration

  3. Basics of Respiration Biologists define respiration as the aerobic harvesting of energy from food molecules by cells

  4. Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels • Cells break down complex organic molecules (rich in potential energy) to simpler waste products (low in potential energy) • To get energy to do work • Rest is given off as heat

  5. Cells do this in two ways: • Fermentation • Cellular respiration

  6. 1) One catabolic process, fermentation • Is a partial degradation of sugars that occurs without oxygen

  7. 2) Cellular respiration • Most prevalent and efficient catabolic pathway • Consumes oxygen and organic molecules such as glucose • Yields more ATP

  8. The equation for the reaction of cellular respiration: C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP & Heat)

  9. Catabolic Pathways and Production of ATP • The breakdown of organic molecules is exergonic • But catabolic pathways don’t do work directly • Just release energy so work can be done

  10. Redox Reactions: Oxidation and Reduction • Catabolic pathways yield energy • Due to the transfer of electrons • When 1 or more electrons transfers from one reactant to another the process is called oxidation reduction reaction or redox for short

  11. The Principle of Redox • Oxidation – loss of an electron • The substance that gives up its electron is the reducing agent • Reduction the gain of an electron • The substance that gains the electron is the oxidizing agent

  12. becomes oxidized(loses electron) Reducing agent Na + Cl Na+ + Cl– becomes reduced(gains electron) Oxidizing agent • Examples of redox reactions

  13. becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced • Specifically in cellular respiration: • Glucose is oxidized and oxygen is reduced • Electrons lose potential energy and energy is released

  14. To Sum Up • Remember an electron loses potential energy when it shifts from a less electronegative atom to a more electronegative atom (oxygen is very electronegative) • So by oxidizing glucose, respiration frees stored energy (in glucose) and makes it available for work (as ATP)

  15. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain • Cellular respiration • Oxidizes glucose in a series of steps • Because energy can’t be released all at once and still be useful

  16. Stepwise Energy Harvest • Glucose is broken down in a series of steps with the help of enzymes • First an electron is taken away from a glucose molecule. But a proton goes with the electron, so in effect a Hydrogen atom was removed • Second it is picked up by a coenzyme NAD+ which will act as an oxidizing agent • NAD+ is reduced to NADH

  17. Stepwise Energy Harvest • Second it is picked up by a coenzyme NAD+ which will act as an oxidizing agent • NAD+ is reduced to NADH • Electrons lose little potential energy going from food to NAD+ • NADH molecule now represents stored energy

  18. Stepwise Energy Harvest • Third NADH will release their electrons down a series of reactions with oxygen being the final electron acceptor (or receptor) • This is known as the Electron Transport Chain and uses the energy from the electron transfer to form ATP

  19. To Sum Up: • The electrons removed from food by NAD+ fall down an energy gradient in the ETC to a far more stable location in the electronegative oxygen atom

  20. The Stages of Cellular Respiration: A Preview • Glycolysis • The citric acid cycle • Oxidative phosphorylation

  21. The first two stages are catabolic pathways that decompose glucose 1) Glycolysis • Occurs in the cytosol • Breaks down glucose into two molecules of pyruvate 2) The citric acid cycle • Occurs in the mitochondrial matrix • Completes the breakdown of glucose

  22. Remember, why do we do this? • Goal of cellular respiration is ATP production • Oxidative phosphorylation - redox rxns of the ETC • Substrate level phosphorylation

  23. Substrate level phosphorylation • ATP is formed directly • Enzymes transfer a phosphate group from a substrate molecule to an ADP (adenosine diphosphate) • Generates ATP directly

  24. Enzyme Enzyme ADP P Substrate + ATP Product Figure 9.7 • Both glycolysis and the citric acid cycle • Can generate ATP by substrate-level phosphorylation

  25. Electrons carried via NADH and FADH2 Electrons carried via NADH Oxidativephosphorylation:electron transport andchemiosmosis Citric acid cycle Glycolsis Pyruvate Glucose Cytosol Mitochondrion ATP ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Substrate-level phosphorylation Figure 9.6 • An overview of cellular respiration

  26. Glycolysis • Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate • Glycolysis • Breaks down 1 glucose into 2 pyruvate • Occurs in the cytoplasm of the cell

  27. Glycolysis Oxidativephosphorylation Citricacidcycle ATP ATP ATP Energy investment phase Glucose P 2 ATP + 2 used 2 ATP Energy payoff phase formed P 4 ATP 4 ADP + 4 2 NAD+ + 4 e- + 4 H + + 2 H+ 2 NADH 2 Pyruvate + 2 H2O Glucose 2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used 2 ATP + 2 H+ 2 NADH 2 NAD+ + 4 e– + 4 H + Figure 9.8 • Glycolysis consists of two major phases • Energy investment phase • Energy payoff phase

  28. A closer look at the energy investment phase • Be thinking: • What do I start with? • What do I add in to this? • What do I get out of this? • Where does this occur?

  29. A closer look at the energy payoff phase • Be thinking: • What do I start with? • What do I add in to this? • What do I get out of this? • Where does this occur?

  30. Citric Acid Cycle • Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules • The citric acid cycle • Takes place in the matrix of the mitochondrion

  31. CYTOSOL MITOCHONDRION + H+ NAD+ NADH O– CoA S 2 C O C O C O CH3 1 3 CH3 Acetyle CoA Pyruvate CO2 Coenzyme A Transport protein Figure 9.10 • Before the citric acid cycle can begin: • Pyruvate must first be converted to acetyl CoA, which links glycolysis to the citric acid cycle This only happens if oxygen is present!

  32. CYTOSOL MITOCHONDRION + H+ NAD+ NADH O– CoA S 2 C O C O C O CH3 1 3 CH3 Acetyle CoA Pyruvate CO2 Coenzyme A Transport protein Figure 9.10 • The carboxyl group is removed (it is fully oxidized so it has little chemical energy left) • First step where CO2 is released

  33. CYTOSOL MITOCHONDRION + H+ NAD+ NADH O– CoA S 2 C O C O C O CH3 1 3 CH3 Acetyle CoA Pyruvate CO2 Coenzyme A Transport protein Figure 9.10 2) Electrons are removed and transferred to NAD+ which stores them as NADH

  34. CYTOSOL MITOCHONDRION + H+ NAD+ NADH O– CoA S 2 C O C O C O CH3 1 3 CH3 Acetyle CoA Pyruvate CO2 Coenzyme A Transport protein Figure 9.10 3) Coenzyme A attaches via an unstable bond, so compound is now highly reactive

  35. Pyruvate(from glycolysis,2 molecules per glucose) Oxidativephosphorylation Glycolysis Citricacidcycle ATP ATP ATP CO2 CoA NADH + 3 H+ Acetyle CoA CoA CoA Citricacidcycle 2 CO2 3 NAD+ FADH2 FAD 3 NADH + 3 H+ ADP + Pi ATP Figure 9.11 • An overview of the citric acid cycle

  36. A closer look at the citric acid cycle • Be thinking: • What do I start with? • What do I add in to this? • What do I get out of this? • Where does this occur?

  37. Citric acid cycle Oxidative phosphorylation Glycolysis S CoA C O CH3 Acetyl CoA CoA SH H2O O C COO– NADH 1 COO– CH2 + H+ COO– CH2 COO– NAD+ Oxaloacetate 8 C COO– HO CH2 2 CH2 HC COO– COO– COO– HO CH HO CH Malate Citrate COO– CH2 Isocitrate COO– CO2 Citric acid cycle 3 H2O 7 NAD+ COO– NADH COO– CH + H+ Fumarate CH2 CoA SH HC a-Ketoglutarate CH2 COO– C O 4 6 SH CoA COO– COO– COO– CH2 5 CH2 FADH2 CO2 CH2 CH2 NAD+ FAD C O COO– Succinate NADH CoA S P i + H+ Succinyl CoA GDP GTP ADP ATP Figure 9.12 Figure 9.12

  38. Oxidative Phosphorylation . . . ETC • Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis • So far, only 4 ATP have been made

  39. The Pathway of Electron Transport • Electron Transport Chain – is a collection of molecules embedded in the inner membrane of the mitochondria • Most components are proteins

  40. NADH 50 FADH2 Multiproteincomplexes I 40 FAD FMN II Fe•S Fe•S O III Cyt b 30 Fe•S Cyt c1 IV Free energy (G) relative to O2 (kcl/mol) Cyt c Cyt a Cyt a3 20 10 0 O2 2 H + + 12 Figure 9.13 H2O • An NADH molecule begins the process by “dropping off” its electron at the first electron carrier molecule

  41. NADH 50 FADH2 Multiproteincomplexes I 40 FAD FMN II Fe•S Fe•S O III Cyt b Fe•S 30 Cyt c1 IV Free energy (G) relative to O2 (kcl/mol) Cyt c Cyt a Cyt a3 20 10 0 O2 2 H + + 12 Figure 9.13 H2O • Remember: each component will be reduced when it accepts the electron and oxidized when it passes the electron down to the more electronegative carrier molecule in the chain

  42. NADH 50 FADH2 Multiproteincomplexes I 40 FAD FMN II Fe•S Fe•S O III Cyt b 30 Fe•S Cyt c1 IV Free energy (G) relative to O2 (kcl/mol) Cyt c Cyt a Cyt a3 20 10 0 O2 2 H + + 12 Figure 9.13 H2O • Finally the electron is passed to oxygen, which is very electronegative. The oxygen also picks up 2 H+ ions from the aqueous solution and forms water

  43. NADH 50 FADH2 Multiproteincomplexes I 40 FAD FMN II Fe•S Fe•S O III Cyt b 30 Fe•S Cyt c1 IV Free energy (G) relative to O2 (kcl/mol) Cyt c Cyt a Cyt a3 20 10 0 O2 2 H + + 12 Figure 9.13 H2O • FADH goes through mostly the same processes, except it drops off its electron at a lower point on the ETC

  44. WARNING: The ETC makes no ATP directly! The ETC releases energy in a step-wise series of reactions. It powers ATP synthesis via oxidative phosphorylation. But it needs to be coupled with chemiosmosis to actually make ATP.

  45. Chemiosmosis: The Energy-Coupling Mechanism • Inner membrane of mitochondria has many protein complexes called ATP synthase • ATP synthase – enzyme that makes ATP from ADP and inorganic phosphate • It uses the energy of an existing gradient to do this.

  46. Inner Mitochondrial membrane Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP H+ H+ H+ H+ Cyt c Protein complex of electron carners Intermembrane space Q IV I III ATP synthase Inner mitochondrial membrane II H2O FADH2 2 H+ + 1/2 O2 FAD+ NADH+ NAD+ ATP ADP + P i (Carrying electrons from, food) H+ Mitochondrial matrix Chemiosmosis ATP synthesis powered by the flow Of H+ back across the membrane Electron transport chain Electron transport and pumping of protons (H+), which create an H+ gradient across the membrane Figure 9.15 Oxidative phosphorylation • The existing gradient is the difference in H+ ion concentration on opposite sides of the inner membrane of the mitochondria

  47. So what is this process called? • Chemiosmosis – the process in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work (like the synthesis of ATP)

  48. Inner Mitochondrial membrane Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP H+ H+ H+ H+ Cyt c Protein complex of electron carners Intermembrane space Q IV I III ATP synthase Inner mitochondrial membrane II H2O FADH2 2 H+ + 1/2 O2 FAD+ NADH+ NAD+ ATP ADP + P i (Carrying electrons from, food) H+ Mitochondrial matrix Chemiosmosis ATP synthesis powered by the flow Of H+ back across the membrane Electron transport chain Electron transport and pumping of protons (H+), which create an H+ gradient across the membrane Figure 9.15 Oxidative phosphorylation • It is the job of the ETC to create this H+ ion gradient

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