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Chapter 9: Cellular Respiration
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  1. Chapter 9: Cellular Respiration Cellular Respiration

  2. Cellular Respiration • Living cells require energy from outside sources • Organisms use as their main energy source • Cellular respiration is the process of breaking down food molecules to • Energy is released in the process of respiration when the cells of plants and animals convert sugar and oxygen into carbon dioxide and water

  3. Respiration • The breakdown of organic molecules is • respiration consumes organic molecules and O2 and yields ATP (oxygen required) • respiration is similar to aerobic respiration but consumes compounds other than O2 (no oxygen required) • is a partial degradation of sugars that occurs without O2

  4. Cellular Respiration • Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration • Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:

  5. Redox Reactions • The transfer of electrons during chemical reactions releases energy stored in organic molecules • This released energy is used to make ATP • Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or • In oxidation, a substance , or is oxidized • In reduction, a substance , or is reduced (the amount of positive charge is reduced) • In cellular respiration, the glucose is and O2 is

  6. NAD+ • 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+ (nicotinamide adenine dinucleotide), a coenzyme • As an electron acceptor, NAD+functions as an • Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP • NADH passes the electrons to the

  7. Electron Transport Chain • Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction • pulls electrons down the chain in an energy-yielding tumble • The energy yielded is used to regenerate

  8. - Anaerobic (breaks down glucose into two molecules of pyruvate) - Aerobic (Kreb’s Cycle - completes the breakdown of glucose) - Aerobic (ETC - accounts for most of the ATP synthesis) Stages of Cellular Respiration

  9. Mitochondria 1) Glycolysis 2) Citric Acid Cycle 3) Oxidative Phosphorylation (ETC)

  10. Step 1: Glycolysis • Breaks down glucose (C6H12O6) into two molecules of pyruvic acid - AKA • Anaerobic • Occurs in the cytoplasm • NAD picks up H+ and electrons to form NADH2

  11. Reactants Products Glycolysis Summary Location: Simple Summary Summary total

  12. Bridge Reaction • In the presence of O2, pyruvate enters the mitochondrion • Before the citric acid cycle can begin, pyruvate must be converted to , which links the cycle to glycolysis • In the mitochondria matrix… 1) Pyruvic Acid loses a C to form acetic acid (2-C) 2) The lost carbon binds with O2 making CO2 3)Acetic acid binds with Coenzyme-A forming Acetyl Co-A

  13. Step 2: The Kreb’s Cycle(Citric Acid Cycle) • Takes place within the mitochondrial matrix • There are , each catalyzed by a specific enzyme • The acetyl group of acetyl CoA joins the cycle by combining with (4-C molecule), forming a 6-C molecule known as • The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle

  14. Step 2: The Kreb’s Cycle(Citric Acid Cycle) • 2 molecules of CO2 are released • (flavin adenine dinucleotide - another ion carrier) pick up electrons and H+ becoming NADH and FADH2 • The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain • The cycle generates 1 ATP, 3 NADH, and 1 FADH2 per turn • Recall that are formed during glycolysis resulting in of the Kreb’s cycle for each glucose molecule!

  15. Reactants Products Kreb’s Cycle Summary Location: Kreb’s Summary Kreb's Summary 2

  16. Step 3: Electron Transport Chain (ETC) • Aerobic process • Requires as the final electron acceptor • Takes place in the cristae of the mitochondria • A series of molecules that excited electrons pass along, to release energy as ATP • Most of the chain’s components are , which exist in multiprotein complexes

  17. Step 3: Electron Transport Chain (ETC) • Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food • These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via • The carriers alternate as they accept and donate electrons • Electrons drop in free energy as they go down the chain • They are finally passed to O2 forming

  18. NADH and FADH2 • Dump the electrons and protons they’ve gathered throughout glycolysis and the citric acid cycle • Again, • O2 + 2e- + 2H+  H2O • Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2 • The chain’s function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts • to generate large amounts of ATP

  19. Chemiosmosis • Electron transfer in the ETC causes proteins to pump from the mitochondrial matrix to the intermembrane space • H+ then moves back across the membrane, passing through channels in (enzyme that acts like an ion pump) • ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ADP • This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work • The H+ gradient is called the ETC Summary

  20. ETC

  21. Reactants Product ETC Summary Location: Simpler ETC Summary Best ETC Summary

  22. Whole Respiration Process

  23. Total Energy Total ATP from 1 molecule of glucose in Stage ATP + 4 Total Glycolysis (b/c 2 are used in the first step) CA Cycle ETC _________________ TOTAL   During cellular respiration, most energy flows in this sequence: Glucose -> NADH -> electron transport chain -> proton-motive force -> ATP

  24. Fermentation • Most cellular respiration requires O2 to produce ATP • Glycolysis can produce ATP (in aerobic or anaerobic conditions) • In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP • Fermentation uses instead of an electron transport chain to generate ATP • 2 Types: • Fermentation • Fermentation

  25. Lactic Acid Fermentation • In lactic acid fermentation, , forming lactate as an end product, with no release of CO2 • Lactic acid fermentation by some fungi and bacteria is used to make • Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

  26. Lactic Acid Fermentation • Example: Burning feeling in muscles during a workout • From oxygen debt • Lactate

  27. Alcohol Fermentation • In alcohol fermentation, pyruvate is converted to (type of alcohol) in two steps, with the first releasing CO2 • Bacteria and fungi (yeast) • Alcohol fermentation by yeast is used in

  28. Fermentation • Obligate anaerobes carry out fermentation or anaerobic respiration and • Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration Review

  29. Role of Macromolecules • Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration • Glycolysis accepts a wide range of • Proteins must be digested to amino acids • Amino groups can feed • Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) • Fatty acids are broken down by beta oxidationand yield • An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate

  30. Regulation of Cell Respiration • Feedback inhibition is the most common mechanism for control • If ATP concentration begins to drop, respiration • When there is plenty of ATP, respiration • Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway

  31. Review Questions Define cellular respiration and state its importance as a life process. Differentiate between aerobic respiration, anaerobic respiration, and fermentation. State and explain the chemical equation for cellular respiration. Define oxidation and reduction and explain the idea of redox reactions. Explain the use of NAD+ as a coenzyme. Explain the electron transport chain (ETC). Name the 3 major stages of cell respiration, along with their locations. Explain glycolysis, stating the reactants, products, and major activities. Explain the bridge reaction, stating the reactants, products, and major activities. Explain the Kreb’s cycle, stating the reactants, products, and major activities. Explain glycolysis, stating the reactants, products, and major activities. Explain the ETC, stating the reactants, products, and major activities. Explain the role of oxygen in the ETC. Define chemiosmosis and explain its role in cellular respiration. Differentiate between lactic acid fermentation and alcohol fermentation. Differentiate between oblicate anaerobes and facultative anaerobes. Explain the role of macromolecules in cellular respiration. Explain how cell respiration is regulated.