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2.2 Cellular Respiration: The Details

2.2 Cellular Respiration: The Details. Energy Carriers. NAD + and FAD + are low energy, oxidized coenzymes that act as electron acceptors. When an electron(s) are added to these molecules, they become reduced to NADH and FADH 2 . In this case, reducing a molecule gives it more energy.

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2.2 Cellular Respiration: The Details

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  1. 2.2 Cellular Respiration: The Details

  2. Energy Carriers • NAD+ and FAD+ are low energy, oxidized coenzymes that act as electron acceptors. • When an electron(s) are added to these molecules, they become reduced to NADH and FADH2. • In this case, reducing a molecule gives it more energy.

  3. Aerobic Respiration: Overview Occurs in Four Distinct Stages: • Glycolysis: 10-step process in the cytoplasm. • Pyruvate Oxidation: 1-step process in the mitochondrial matrix. • Krebs Cycle: 8-step cyclical process in the mitochondrial matrix. • Electron Transport Chain & Chemiosmosis: Multi-step process in the inner mitochondrial membrane.

  4. Energy Transfer Terminology Substrate-level Phosphorylation: • ATP forms directly in an enzyme-catalyzed reaction. Oxidative Phosphorylation: • ATP forms indirectly through a series of enzyme-catalyzed redox reactions involving oxygen as the final electron acceptor.

  5. Glycolysis • 2 ATPs are used in steps 1 & 3 to prepare glucose for splitting. • F 1,6-BP splits into DHAP and G3P. • DHAP converts to G3P. • 2 NADH are formed in step 6. • 2 ATP are formed by substrate-level phosphorylation in both steps 7 and 10. • 2 pyruvates are produced in step 10.

  6. Glycolysis Energy Yield & Products: 4 ATP produced – 2 ATP used = 2 net ATP 2 NADH 2 pyruvates Further processing in aerobic cellular respiration (if oxygen is available)

  7. Highly folded Smooth Fluid-filled intermembrane space Folds of the inner membrane Protein-rich liquid Mitochondria

  8. Pyruvate Oxidation(if oxygen is present…) The following occurs for each pyruvate: • CO2 removed. • NAD+ reduced to NADH and the 2-carbon compound becomes acetic acid. • Coenzyme A (CoA) attaches to acetic acid to form acetyl-CoA.

  9. Pyruvate Oxidation

  10. Pyruvate Oxidation Energy Yield & Products: 2 NADH 2 acetyl-CoA 2 CO2 (released as waste)

  11. The Krebs Cycle Occurs twice for each molecule of glucose, 1 for each acetyl-CoA.

  12. The Krebs Cycle • In step 1, acetyl-CoA combines with oxaloacetate to form citrate. • In step 2, citrate is rearranged to isocitrate. • NAD+ is reduced to NADH in steps 3, 4 and 8. • FAD is reduced to FADH2 in step 6. • ATP if formed in step 5 by substrate-level phosphorylation. The phosphate group from succinyl-CoA is transferred to GDP, forming GTP, which then forms ATP. • In step 8, oxaloacetate is formed from malate, which is used as a reactant in step 1. • CO2 is released in steps 3 and 4.

  13. The Krebs Cycle Energy Yield & Products: 2 ATP 6 NADH 2 FADH2 4 CO2 (released as waste) NADH and FADH2 carry electrons to the electron transport chain for further production of ATP by oxidative phosphorylation.

  14. Electron Transport Chain (ETC) • A series of electron acceptors (proteins) are embedded in the cristae. • These proteins are arranged in order of increasing electronegativity. • The weakest attractor of electrons (NADH dehydrogenase) is at the start of the chain and the strongest (cytochrome oxidase) is at the end.

  15. Electron Transport Chain (ETC) • These proteins pass electrons from NADH and FADH2 to one another through a series of redox reactions. • ETC protein complexes are alternately reduced and oxidized as they accept and donate electrons.

  16. Electron Transport Chain (ETC) • As the electrons pass from one molecule to the next, it occupies a more stable position. • The free energy released is used to pump protons (H+) to the intermembrane space. • 3 for every NADH and 2 for every FADH2. • This creates an electrochemical gradient, creating potential difference (voltage) similar to a battery.

  17. Electron Transport Chain (ETC) • Protons are forced to pass back into the matrix through special proton channels associated with ATP synthase (ATPase). • For every H+ that passes through, enough free energy is released to create 1 ATP from the phosphorylation of ADP. • Conditions must be aerobic because oxygen acts as the final electron and H+ acceptor (water is formed as a byproduct).

  18. Electron Transport Chain (ETC) NADH dehydrogenase Cytochrome b-c1 complex FADH2 FAD+

  19. ATP Yield from Aerobic Respiration

  20. Controlling Aerobic Respiration • Regulated by feedback inhibition and product activation loops. • Phosphofructokinase is an allosteric enzyme that catalyzes the third reaction in glycolysis and is inhibited by ATP and stimulated by ADP. • If citrate (first product of Krebs cycle) accumulates, some will pass into the cytoplasm and inhibit phosphofructokinase and slow down glycolysis. • As citrate is used up, its concentration will decrease and the rate of glycolysis will increase.

  21. Controlling Aerobic Respiration • A high concentration of NADH indicates that the ETCs are full of electrons and ATP production is high. • NADH allosterically inhibits an enzyme that reduces the amount of acetyl-CoA that is shuttled to the Krebs cycle, reducing the amount of NADH produced.

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