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Cellular Respiration

This text explains the process of cellular respiration, where glucose is broken down to produce ATP through a series of redox reactions. It covers the phases of glycolysis, preparatory reaction, citric acid cycle, and electron transport chain.

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Cellular Respiration

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  1. Cellular Respiration Breakdown of glucose to carbon dioxide and water

  2. Redox reaction • Hydrogen atoms consist of a hydrogen ion and an electron (H+ and e-) • Glucose is oxidized when the hydrogen is removed • Oxygen is reduced when it gains hydrogen and becomes water • Exergonic reaction – glucose is a high energy molecule  water and carbon dioxide are low energy molecules

  3. ATP • Build up of ATP = endergonic • Glucose is broken down slowly, ATP produced gradually • Maximum production of ATP = 36 – 38 • 39% efficiency from glucose to ATP

  4. Coenzymes • NAD+ (nicotinamide adenine dinucleotide) • Accepts 2 electrons and 1 hydrogen = NADH • FAD (flavin adenine dinucleotide) • Accepts 2 electrons and 2 hydrogens = FADH2

  5. Making of ATP • Oxidative phosphorylation – ATP made by the redox reactions of the Electron Transport Chain (ETC and Chemiosmosis) • Accounts for 90% of the ATP generated in respiration • Substrate Level Phosphorylation – enzyme transfer a P group from a substrate molecule to ATP

  6. Phases of cellular respiration • Glycolysis – outside mitochondria, anaerobic, splitting of glucose – 2 pyruvate, yield 2 ATP • Preparatory reaction – in mitochondria, pyruvate oxidized to 2 – C acetyl group, preps for citric acid cycle • Citric acid cycle – (Krebs) in matrix of mitochondria, yield 2 ATP • Electron transport chain – cristae, oxygen is final electron acceptor and forms water, result in 32 – 34 ATP

  7. Glycolysis – see handout/text • Outside of mitochondria in cytoplasm • Glucose  2 pyruvate • Does not require oxygen, anaerobic

  8. Energy investment • 2 ATP are used to activate glucose and break down into 2 C3 molecules of G3P.

  9. Energy harvesting • Electrons removed (oxidation) with hydrogen ions. • NAD picks up Hydrogen and electrons = NADH • Substrate level phosphorylation – production of ATP via an enzyme passing a high energy phosphate to ADP = 4 ATP • Investment of 2 ATP minus 4 ATP = 2 net ATP

  10. Prep Reaction • Pyruvate (2 C3 molecules) is converted to an acetyl group (C2) that is attached to coenzyme A (CoA) • CO2 is a product • Oxidation occurs, electrons from pyruvate are removed, NAD  NADH • Reaction occurs twice since there are 2 pyruvate per glucose molecule

  11. Prep Reaction

  12. Prep reaction • Inputs: 2 pyruvate, 2 NAD+, 2 CoA • Outputs: 2 CO2 (Product), 2 NADH, 2 acetyl CoA

  13. Citric Acid Cycle • Matrix of mitochondria • C2 (acetyl CoA) joins with C4 molecule = C6 citrate molecule. • Each acetyl group is oxidized to 2 CO2 molecules = 4 CO2 total released • Cycle goes around 2 times

  14. Citric Acid Cycle • Substrate Level phosphorylation - An enzyme passes a high energy phosphate to ADP = ATP • Inputs: 2 acetyl CoA, 6 NAD, 2 ADP/P, 2 FAD • Outputs: 4 CO2 (product), 6 NADH, 2 FADH2, 2 ATP

  15. Prep reaction  Citric acid cycle • Cycle goes around 2 times

  16. Electron Transport Chain • Electrons are carried by NADH and FADH2 • Oxidation-reduction reaction starts the ETC. High energy electrons enter the chain, low energy electrons leave. • There is a series of carriers that transport the electrons, first reduced when it accepts the electrons, then oxidized when it releases them.

  17. Carriers • 3 protein complexes (NADH-Q reductase, cytochrome reductase and cytochrome oxidase) • 2 carriers that transport electrons on ETC– coenzyme Q and cytochrome c • Cytochrome – protein that has a tightly bound heme group with a central atom of iron.

  18. Oxidative phosphorylation • Hydrogen ions are pumped out of the matrix into the intermembrane space, H+ flow back through membrane due to H+ gradient = chemiosmosis • Production of ATP as a result of energy released by the ETC = 32 – 34 ATP • Production of ATP via substrate phosphorylation is 4 ATP • Total ATP = 36 – 38 ATP 39% efficiency of cellular resp.

  19. ETC • For each NADH that is oxidized, 3 ATP molecules are produced • For each FADH2 that is oxidized, 2 ATP are produced, (due to the fact that they follow NADH and electrons are at a lower energy level).

  20. Electron transport chain • Oxygen is the final electron acceptor in the ETC • Receives last electrons and combines with the hydrogen ions to form water (product)

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