Cellular Respiration and Fermentation

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Cellular Respiration and Fermentation

• Chapter 9
• Unit 3

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Catabolic Pathways

• Fermentation
• Partial breakdown of sugars
• anaerobic
• Cell Respiration
• Most prevalent and efficient
• Complete breakdown of sugars
• aerobic

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Redox Reactions Oxidation and Reduction

• Transfer of e- from one reactant to another
• Oxidation loss of electrons
• Reduction addition of electrons to another
  substance
• Reducing agent electron donor (C6H12O6)
• Glucose reduces oxygen which accepts the e-
• Oxidizing agent electron acceptor (6O2)
• Oxidizes glucose by accepting the e-

C6H12O6 6O2 ? 6H2O 6CO2
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Energy Harvest via NAD

• Energy is released as electrons fall from
  organic molecules to O2
• Broken down into steps
• Coenzyme NAD electron acceptor
• NAD picks up 2e- and 2H ? NADH (stores E)
• NADH carries electrons to the electron transport
  chain (ETC)
• ETC transfers e- to O2 to make H2O releases
  energy

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Substrate-Level Phosphorylation

• Phosphorylation enzyme transfers a phosphate
  from a substrate to ADPother compounds
• Mode of ATP synthesis
• ADP Pi ? ATP

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Stages of Cellular Respiration

• Glycolysis
• Pyruvate oxidation and krebs
• Oxidative Phosphorylation ETC and chemiosmosis

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Glycolysis

• sugar splitting
• Believed to be ancient (early prokaryotes)
• Occurs in cytosol
• Partially oxidizes glucose (6C) to 2 pyruvates
  (3C)
• Net gain 2 ATP 2NADH
• Also makes 2H2O
• Anaerobic

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Occurs in two Phases

• Energy-investment phase uses two molecules of
  ATP (5 steps)
• Energy yielding phase produces four ATP
  molecules and reduces two molecules of NAD to
  NADH
• The junction between Glycolysis and the Krebs
  cycle is the oxidation of pyruvate to acetyl CoA.
• two acetyl fragments are produced

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Mitochondrion Structure
Citric Acid Cycle (matrix)
ETC (inner membrane)
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Oxidation of Pyruvate

• Eukaryote-gt mitochondria
• Prokaryotes-gt cytosol
• Pyruvate is converted to coenzyme A (acetyl CoA)

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Krebs Cycle (Citric acid cycle)

• Occurs in the mitochondrial matrix
• aerobic
• Completes glucose oxidation by breaking down
  acetyl CoA into 3 molecules of carbon dioxide
• Net gain 2 ATP, 6 NADH, 2 FADH2

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Krebs cycle Evolution

• Evolved later than glycolysis
• bacteria ?3.5 billion years ago (glycolysis)
• free O2 ?2.7 billion years ago (photosynthesis)
• eukaryotes ?1.5 billion years ago (aerobic
  respiration organelles ? mitochondria)

Hans Krebs 1900-1981
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The Electron Transport Chain

• electron-carrier molecules built into the inner
  mitochondrial membrane
• Does not make ATP directly
• Eases the fall of e- from food to oxygen
• Oxygen final electron acceptor

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Sequence of electron transfers along the electron
transport chain
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Chemiosmosis

• ATP production
• This is accomplished by creating a proton
  gradient
• ATP synthase
• Cristae

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How chemiosmosis works

• the electron transport chain creates the proton
  gradient by pumping H from the mitochondrial
  matrix
• the membranes phospholipid bilayer is
  impermeable to Hs and prevents back flow
• As protons diffuse through the ATP synthase
  complex phosphorylation of ADP occurs

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Anaerobic Respiration

• Prokaryotes who live in environments w/o Oxygen
• Generate ATP using other electron acceptors
  besides O2
• EX sulfur reducing bacteria use sulfate ions at
  the end of their ETC
• Hydrogen sulfide is produced
• Rotten egg odor in salt marshes or mud flats

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Types of Fermentation

• Extension of glycolysis that allows continuous
  generation of ATP
• Types
• Alcoholic Fermentataion
• Pyruvate is converted to ethanol
• CO2 is released as it is converted to
  acetaldehyde
• Acetaldehyde is reduced by NADH to ethanol
• Regenerates NAD needed for glycolysis

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• Lactic Acid Fermentation
• Pyruvate is reduced by NADH to form lactate as an
  end product
• Lactate that accumulates in muscle cells was
  thought to cause muscle fatigue and pain, but now
  it is suggested that pain comes from increased
  levels of K
• Lactate appears to enhance muscle performance
• Lactate is carried by the blood to the liver
  where it is converted back to pyruvate.

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Anaerobes

• Obligate Anaerobes carry out fermentation or
  anaerobic respiration
• Cannot survive in presence of Oxygen
• EX vertebrate brain cells cannot carry out
  fermentation
• Facultative Anaerobes use either fermentation or
  respiration
• Consumes more sugar when fermenting than
  respiring to make same amt. of ATP
• EX yeast, bacteria, muscle cells

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Glycolysis
O2 present
Without O2

• Fermentation

• Respiration

• Keep glycolysis going by regenerating NAD
• Occurs in cytosol
• No oxygen needed
• Creates ethanol CO2 or lactate
• 2 ATP (from glycolysis)

• Release E from breakdown of food with O2
• Occurs in mitochondria
• O2 required (final electron acceptor)
• Produces CO2, H2O and up to 32 ATP