Chapter 9

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• Chapter 9 Cellular Respiration Harvesting
  Chemical Energy

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Energy Flow

• Energy flow in an ecosystem
• Enters as sunlight, leaves as heat
• Produces ATP
• Involves photosynthesis and cellular respiration

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REDOX Reactions

• Transfer of 1 or more electrons
• Oxidation partial or complete loss of electrons
• Reduction partial or complete gain of electrons
• OIL RIG oxidation is losing, reduction is
  gaining
• Oxidizing agent is the electron acceptor
• Reducing agent is the electron donor
• Simple non-biological example
• Na Cl ? Na Cl-
• Na becomes oxidized (loses electron) while Cl
  becomes reduced (gains electron)
• Na is the reducing agent, Cl is the oxidizing
  agent

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REDOX cont.

• Cellular Respiration
• C6H12O6 6O2 ? 6CO2 6H2O energy (ATP)
• C6H12O6 becomes oxidized to CO2
• O2 becomes reduced to H2O
• Once activation energy barrier breeched, release
  686 kcal or 2870 kJ per mole of glucose
• Use this energy to make ATP (yields 7.3 kcal or
  30.5 kJ/mole)
• Enzymes help to breech the activation energy

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Electron Transfer

• If the energy from glucose is released all at
  once, it cannot be harnessed efficiently
• Use the coenzyme NAD (nicotinamide adenine
  dinucleotide)

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Electron Transport Chains

• How do electrons that are extracted from glucose
  and stored as NADH finally reach oxygen?
• Use electron transport chains to break the fall
  of electrons into several energy releasing steps

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Stages of Cellular Respiration

• 1. Glycolysis breaks glucose into 2 pyruvates
• 2. The Citric Acid Cycle completes the
  breakdown of glucose by oxidizing pyruvate into
  carbon dioxide
• 3. Oxidative phosphorylation electron transport
  and chemiosmosis produces ATP

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Stages of Cellular Respiration
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Glycolysis

• sugar splitting
• Energy investment phase 2 ATP, split glucose
  into 2, 3C intermediates
• Energy payoff phase form 4 ATP, 2 NADH, 2
  waters, and 2, 3C pyruvate molecules

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Glycolysis

• Animation
• ..\ppt lectures cd\animations\09_09Glycolysis_A.sw
  f
• The net gain of 2 ATP made by substrate
  phosphorylation

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Oxidation of Pyruvate (pre-TCA)

• Completes the oxidation of glucose, currently in
  the form of pyruvate
• Pyruvate from cytosol moves into the mitochondria
  via a transport protein
• The carboxyl group (already oxidized) is removed
  and given off as CO2
• Remaining 2 carbon molecule oxidized into acetate
  while the electrons are transferred to NAD
• Coenzyme A is attached to acetate to make acetyl
  CoA

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The Citric Acid Cycle

• Acetyl CoA enters the Citric Acid Cycle by
  combining with oxaloacetate to form citrate
• Exergonic cycle energy used to reduce NAD and
  FAD
• For every turn of the cycle
• 2 carbon atoms enter while 2 different carbons
  leave as CO2
• Coenzymes are reduced 3 NADH and 1FADH2
• 1 ATP produced through substrate-level
  phosphorylation
• Oxaloacetate is regenerated
• 2 turns of the cycle required to completely
  oxidize 1 glucose

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TCA Cycle

1. Acetyl CoA enters making citrate
2. Converted to isocitrate
3. Lose CO2, reduce NAD to NADH
4. Lose CO2, reduce NAD, attached to CoA
5. Add P, remove P, attach to GDP ? GTP ? ADP ? ATP
6. Remove 2 H, form FADH2
7. Add H2O, rearrange
8. Reduce NAD, reform oxaloacetate

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The Citric Acid Cycle

• Animation
• ..\ppt lectures cd\animations\09_12CitricAcidCycle
  _A.swf

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Electron Transport Chain

• Made of proteins embedded in the inner
  mitochodrial membrane, mostly cytochrome proteins
• The electrons fall from NADH to Oxygen yielding
  53 kcal/mol, but not all at one time
• Energy released is coupled to chemiosmosis
• Animation
• Animation2

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Electron Transport
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ATP Synthase

• Makes ATP from ADP and inorganic phosphate
• Works like a reverse ion pump
• H ions move through the protein causing the
  addition of phosphate to ADP
• Animation
• Experiment animation

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Chemiosmosis

• NADH and FADH2 shuttle high energy electrons to
  the electron transport chain
• Energy from these electrons shuttles H ions from
  matrix to intermembrane space
• Creates a concentration gradient, H ions move
  through ATP synthase via facilitated diffusion
  back to the matrix
• Creates ATP from ADP and inorganic phosphate

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ATP Production Overview
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ATP Totals

• Why 36 to 38 ATP? Why not an exact number?
• The phosphorylation and redox reactions are not
  directly coupled. 1 NADH results in 10 H, takes
  3 to 4 H to make ATP, so yield is between 2.5
  and 3.3 ATP. 1 FADH2 yields between 1.5 and 2
  ATP.
• Electrons in NADH outside of mitochondria must be
  passed into the mitochondria through an electron
  shuttle (NADH impermeable to membrane) and
  transferred to either NAD (liver, heart) or FAD
  (brain).
• Some of the proton motive force is used to pull
  in pyruvate from cytosol.
• Approximatelyl 40 of the energy in glucose is
  transferred to ATP, the rest is lost as heat.

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Fermentation

• In the absence of oxygen (anerobic)
• Alcohol Fermentation in many bacteria and yeast
• Lactic Acid Fermentation in human muscles
• Net yield 2 ATP, from glycolysis

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Question

• The oxidation of glucose to carbon dioxide
  releases 277.4 kcal/mole of energy. If all of
  this energy is released at one time, then most of
  it would be lost as heat. Burning the energy all
  at once would be akin to igniting your gas tank
  in order to run your car, rather than burning
  small amounts of gasoline slowly in the engine.
  If the energy of glucose is released slowly, in
  several small steps, then the potential energy
  available could be captured at each step rather
  than a single explosive release.
• In groups of 3 answer the following questions
• How are the steps in the cell respiration process
  consistent with the concepts of stepwise release
  of energy to capture the maximum amount of
  potential energy?
• Explain how it is better for a cell to use many
  reactions to oxidize glucose even though each
  reaction needs a specific enzyme (which is costly
  to the cell to produce).