Cellular Respiration

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CHAPTER 9

• Cellular Respiration

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• Energy flows into most systems as sunlight
• Photosynthetic organisms trap sunlight
• chemical energy as organic molecules
• Cells use organic molecules to make ATP
• cellular respiration
• Energy dissipates as heat

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• 6CO2 6H2O light energy ? C6H12O6 6O2
• Photosynthesis
• C6H12O6 6O2 ? 6CO2 6H2O ATP (chemical
  energy)
• Cellular respiration

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Energy Production

• Oxidation-Reduction reactions (redox reaction)
• oxidation
• reduction
• always coupled
• In most systems electrons and protons are removed
  at the same time
• the equivalent of a hydrogen atom

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• Xe- Y-------------gt X Ye-
• Substance X lost an electron, so it was oxidized
• acts as a reducing agent - reduces Y
• Substance Y gained an electron, so it was reduced
• acts as an oxidizing agent - oxidized X

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When electrons move to more electronegative
atoms, there is lose of potential energy Redox
reactions that move electrons closer to oxygen
release energy
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Reduction of NAD
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Generation of ATP

• Cells drive metabolic activities by releasing
  energy from organic compounds and converting it
  to chemical energy of ATP through phosphorylation
• Types of phosphorylation
• Substrate-Level Phosphorylation
• Oxidative Phosphorylation
• Photophosphorylation

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CH2O Catabolism

• Most of the energy a cell needs is produced by
  oxidizing carbohydrates (CH2O)
• Glucose is 1 source
• Two types of catabolism
• Respiration (aerobic and anaerobic)
• Fermentation (anaerobic only)

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Cellular Respiration and Fermentation
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GLYCOLYSIS

• First energy-releasing stage
• Glucose is partially broken down into 2 molecules
  of pyruvate
• Anerobic
• Occurs in cytoplasm
• 2 NADH and 4 ATP formed per glucose
• 2 ATP consumed so the net gain is 2 ATP
• Substrate level phosphorylation

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KREBS CYCLE

• Second stage of respiration
• Anaerobic, cell membrane or mitochondria
• Each pyruvate must give up a carbon atom (as CO2)
  to form a 2 carbon acetyl
• Decarboxylation
• The acetyl joins with coenzyme A
• acetyl-CoA
• Acetyl-CoA transfers its 2-carbon group to a 4
  carbon oxaloacetic acid
• pick-up molecule of the Krebs cycle
• Oxaloacetate is regenerated with every turn

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• For each pyruvate that enters the Krebs cycle
• 3 CO2
• 1 ATP
• 4 NADH
• 1 FADH2
• The Kreb cycle occurs twice per glucose
• Net yield of product per glucose molecule
• 6 CO2
• 2 ATP
• 8 NADH 3 ATP
• 2 FADH2 2 ATP

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ELECTRON TRANPORT CHAIN

• 3rd and final stage of respiration Aerobic or
  anaerobic
• Inner mitochondrial membrane in eukaryotes and
  plasma membrane in prokaryotes
• Electrons move through the system and set up H
  gradients that drive chemiosmosis
• Oxygen is the final electron acceptor in aerobic
  respiration
• In anaerobic respiration, the final electron
  acceptor is another inorganic substance (CO2,
  NO3, SO42)

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Oxidative Phosphorylation series of redox
reactions creating a stepwise release of energy
to drive chemiosmosis
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Chemiosmosis
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Summary of Respiration

• 4 net ATP formed in glycolysis and Kreb cycle
• substrate-level phosphorylation
• 10 NADH and 2 FADH2 formed during glycolysis and
  the Krebs cycle
• deliver electrons and hydrogen that help to drive
  the formation of 28 ATP by electron transport
  chain
• Typical net energy yield is 36 ATP for eukaryotes
  and 38 for prokaryotes
• H2O and CO2 are by-products of aerobic
  respiration
• By-pyroducts of anaerobic respiration include H2S
  and CH4
• Anaerobic respiration always has a lower energy
  yield

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1 NADH 3 ATP 1 FADH2 2 ATP
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Formula for the complete oxidation of glucose

• C6H12O6 6O2 36ADP 36P ? 6CO2 6H2O 36ATP
• (eukaryote)
• C6H12O6 6O2 38ADP 38P ? 6CO2 6H2O 38ATP
• (prokaryote)

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Fermentation

• A metabolic process that
• Releases energy from an organism molecule (e.g.
  glucose)
• Does not require O2, Krebs cycle, or electron
  transport system
• Involves only glycolysis
• Uses an organic molecule as final electron
  acceptor
• Function
• Produces small amount of ATP (2 ATP/glucose)
• Recycles NADH to NAD
• Occurs in the cytoplasm

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Fermentative Routes of ATP Formation

• Lactate fermentation
• The 2 pyruvate molecules that are formed in
  glycolysis are converted to 2 lactate molecules
• The pyruvate molecules accept the electrons from
  NADH and regenerate NAD
• A net yield of only 2 ATP occurs
• Some organisms rely exclusively on this metabolic
  pathway
• Ex. Lactobacillus bacteria that can produce
  cheeses, yogurt, and sauerkraut

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• Alcohol fermentation
• Enzymes convert each pyruvate molecule to an
  intermediate form acetaldehyde
• The NADH transfers electrons and hydrogen to
  acetaldehyde to form ethanol (an alcohol)
• Certain species of single-celled fungi called
  yeasts are known for their use of this pathway
• EX. Saccharomyces cerevisiae makes bread dough
  rise and Saccharaomyces llipsoideus ferment wine
  from grapes

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