Chapter 6: How Cells Harvest Chemical Energy

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Lecture 11

• Chapter 6 How Cells Harvest Chemical Energy

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Learning Objectives

• Discuss
• Redox reactions
• Electron transport chain
• Phosphorylation
• Recall
• What NAD stands for

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Learning Objectives (Contd)

• Recall
• The 3 basic types of respiratory poisons
• How cyanide, rotenone, CO work
• Define
• ATP synthase
• Justify why metabolic efficiency is only 40

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Cellular Respiration

• Basic version
• Oxygen into cell, carbon dioxide out
• More advanced
• Sugars oxygen CO2 Water Energy
• Today
• C6H12O6 6O2 6CO2 6H20 Energy

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Metabolic Efficiency

• Remember 2nd Law of Thermodynamics
• Bodys efficiency compares well
• Body 40 efficient
• Cars only 25 efficient

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Electron Transport Chain

• Electron transfer powers ATP synthesis
• Occurs by series of Redox reactions
• Remember ATP is rechargeable battery of cell

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Oxidation Reduction

• Loss of electrons is oxidation
• Gain of electrons is reduction
• (remember electrons have neg. charge)

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Redox Electron Transfer

• Redox reaction electron transfer, where one
  molecule oxidized, while another is reduced

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NAD

• First step in electron transport chain
• Receives electrons from organic molecules (like
  sugars)
• NAD is nicotinamide adenine dinucleotide
• When reduced, becomes NADH

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Intermediate Reactions

• Here, electron transfer powers ATP synthesis
• Several reactions, occurring in sequence

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Oxygen (O2)

• Last step in electron transport chain
• Very good at accepting electrons
• The ultimate electron acceptor in cell

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Kodanis Dam Metaphor

• If powering ATP synthesis is producing
  electricity, then
• Electrons water
• Organic molecules clouds
• NAD rain
• NADH lake
• Electron transport chain dams on the river
• Oxygen ocean

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Seventh Inning Stretch
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How is ATP Charged?

• ATP phosphorylated (remember add 3rd phosphate
  to ADP)
• Done by ATP synthase
• An enzyme
• The battery charger of the cell

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Where?

• In the mitochondrial membrane

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Power for ATP Synthase

• ATP Synthase powered by H gradient
• Electron transport chain builds gradient

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Respiratory Poisons

• 3 Basic types
• Act by stopping cellular respiration

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Respiratory Poisons (Contd)

• Some block the electron transport chain
• Rotenone
• Cyanide
• Carbon Monoxide (CO)

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Respiratory Poisons (Contd)

• Some block ATP synthase
• The antibiotic oligomycin
• Kills fungi
• Cant get into our skin cells

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Respiratory Poisons (Contd)

• Some perforate mitochondrial membrane
• H ions leak in
• Gradient effectively destroyed

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Mitochondrial Membrane
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Question

• Why is human metabolic efficiency only 40?

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Answer

• Metabolic efficiency of a human is only 40
  because
• 2nd Law of Thermodynamics
• Electron transport chain has
• Many energy transfers
• Many energy conversions