Nerve activates contraction

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CHAPTER 9 CELLULAR RESPIRATION

• 1. Cellular respiration and fermentation are
  catabolic, energy-yielding pathways
• 2. Cells recycle the ATP they use for work
• Redox reactions movement of electrons
• Electrons fall in steps during cellular
  respiration
• Respiration involves (a) glycolysis, (b) Krebs
  cycle, and (c) electron transport
• Glycolysis oxidizes glucose to pyruvate
• The Krebs cycle completes pyruvate oxidation in
  steps
• Electron transport sythesizes ATP in
  mitochondrial membranes
• Summary

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• Cells require energy from outside sources to
  continue work.

Fig. 9.1
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1. Cellular respiration and fermentation are
catabolic, energy-yielding pathways

• Organic molecules store energy in their
  arrangement of atoms.
• Enzymes systematically catalyze the breakdown of
  organic molecules to simpler products (with less
  energy).
• Some of the released energy is used to do work
  and the rest is dissipated as heat.

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• One type of catabolic process, fermentation,
  partial degrades sugars in the absence of oxygen.
• Cellular respiration uses oxygen as a reactant to
  complete the breakdown of a variety of organic
  molecules.
• Much more efficient than fermentation.
• Most cellular respiration occur in mitochondria.
• Organic compounds O2 -gt CO2 H2O Energy

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• Carbohydrates, fats, and proteins can all be used
  as the fuel, but consider glucose alone
• C6H12O6 6O2 -gt 6CO2 6H2O Energy (ATP
  heat)
• The catabolism of glucose is exergonic
• ?G - 686 kcal per mole of glucose.
• Some of this energy is used to produce ATP that
  will perform cellular work.

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2. Cells recycle the ATP they use for work

• Cells regenerate ATP from ADP and Pi by the
  catabolism of organic molecules.
• The price of most cellular work is the conversion
  of ATP ADP Pi.

Fig. 9.2
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3. Redox reactions movement of electrons

• Reactions that transfer gt 1 electron from one
  reactant to another are reduction-oxidation
  reactions, or redox reactions.
• The addition of electrons is called reduction
  (makes it more negative by adding e-).
• The loss of electrons is called oxidation.
• Na Cl -gt Na Cl-
• Na is __________ and Cl is __________

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4. Electrons fall in steps during cellular
respiration

• C6H12O6 6O2 -gt 6CO2 6H2O
• Glucose is oxidized, oxygen is reduced, and
  electrons lose potential energy.
• Electrons associated with hydrogen are ready
  sources of electrons to reduce oxygen.
• Oxygen is our terminal electron receptor in a
  chain of steps.
• Enzymes lower the barrier of activation energy,
  allowing these fuels to be oxidized slowly.

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• Glucose etc. are broken down gradually in a
  series of steps, each catalyzed by a specific
  enzyme.
• H atoms are stripped from glucose stepwise - and
  passed to a coenzyme, like NAD (nicotinamide
  adenine dinucleotide).
• The oxidized form NAD is reduced to NADH.
• Electrons carried by NADH lose very little of
  their potential energy in this process (most of
  energy is transferred without loss).

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• NADH energy is used to synthesize ATP as
  electrons fall from NADH to oxygen.
• Series of reactions occur via proteins, etc.
  in/on membranes inside mitochondria.
• NADH shuttles electrons from food to the top of
  the chain.
• At the bottom, oxygen accepts the electrons and
  H to form water.
• ?G from top to bottom -53 kcal/mole of NADH.

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5. Respiration involves (a) glycolysis, (b) the
Krebs cycle, and (c) electron transport
Fig. 9.6
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• Oxidative phosphorylation produces 90 of the
  ATP generated by respiration.
• Some ATP from glycolysis and the Krebs cycle by
  substrate-level phosphorylation.

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• Substrate-level phosphorylation an enzyme
  transfers a PO4 from the substrate to ADP,
  forming ATP.

Fig. 9.7
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6. Glycolysis oxidizes glucose to pyruvate

• Glucose (6 carbon-sugar) is split into two,
  three-carbon sugars.
• These smaller sugars are oxidized and rearranged
  to form two molecules of pyruvate.
• 10 steps each is catalyzed by a specific enzyme.
• These steps can be divided into two phases an
  energy investment and an energy payoff.

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• Energy investment ATP provides activation energy
  by phosphorylating glucose.
• Costs 2 ATP per glucose.
• Energy payoff ATP produced by substrate-level
  phosphorylation and NAD is reduced to NADH.
• Yields 4 ATP 2 NADH per glucose.

Fig. 9.8
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• Net yield from glycolysis 2 ATP and 2 NADH per
  glucose.
• No CO2 is produced during glycolysis.
• Glycolysis occurs whether O2 is present or not.
• If O2 is present, pyruvate moves to the Krebs
  cycle, NADH ? ATP by the electron transport
  system and oxidative phosphorylation.
• What happens if O2 is not available?

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7. The Krebs cycle completes pyruvate oxidation
in steps

• gt ¾ of original energy in glucose is still
  present in two molecules of pyruvate.
• If oxygen is present, pyruvate enters the Krebs
  cycle.
• Pyruvate is converted to acetyl CoA - this
  enters the Krebs cycle.
• Net Yield 2 NADH per glucose.

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Krebs Cycle Net Yields

• 3 NADH
• 1 ATP
• 1 FADH2

per pyruvate
OR

• 6 NADH
• 2 ATP
• 2 FADH2

per glucose
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8. Electron transport synthesizes ATP in
mitochondria membranes

• Majority of ATP comes from the energy in the
  electrons carried by NADH (and FADH2).

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• Electrons carried by NADH are transferred to
  molecules in the electron transport chain
• Electrons carried by FADH2 have lower free energy
  and are added to a later point in the chain.
• Electrons from NADH or FADH2 ultimately pass to
  oxygen.

Wheres the ATP?
Fig. 9.13
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• A protein complex, ATP synthase, in the cristae
  makes ATP from ADP and Pi.
• Proton gradient powers ATP synthesis.
• This proton gradient develops between the
  intermembrane space and the matrix.

Fig. 9.14
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1 NADH ? 3 H Each H ? 1 ATP So each NADH ? 3
ATPs
Fig. 9.15
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• The ATP synthase molecules are the only place
  that will allow H to diffuse back to the matrix.
• This exergonic flow of H is used by the enzyme
  to generate ATP (chemiosmosis).
• Also in chloroplasts, but light drives the
  electron flow.
• Prokaryotes generate H gradients across their
  plasma membrane - generate ATP, pump nutrients
  and waste products across the membrane, rotate
  flagella.

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9. Summary

• Most energy flows from glucose -gt NADH -gt
  electron transport chain ? proton pump ? ATP.
• Each NADH yields about 3 ATP.
• Each FADH2 yields about 2 ATP.
• Note in some eukaryotes NADH from glycolysis
  yields only 2 ATP.

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• Assume the most energy-efficient system
• 34 ATP is produced by oxidative phosphorylation.
• 4 ATP from substrate-level phosphorylation.
• Total 38 ATP (max).

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Fig. 9.16 good summary
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• How efficient is respiration in generating ATP?
• Complete oxidation of glucose releases 686 kcal /
  mole.
• Formation of each ATP requires at least 7.3
  kcal/mole.
• 7.3 kcal/mole x 38 ATP/glucose
• 686 kcal/mole glucose
• The other approximately 60 is lost as heat.
• So how does that compare to other energy machines?

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Incandescent light bulbs lt 20 Internal
combustion engine 20-25