Bioenergetics

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Bioenergetics
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Oxidation and Reduction

• Oxidation is the Loss of Electrons
• E.g., something that is oxidized in the course of
  a chemical reaction with Oxygen has had electrons
  stolen by Oxygen
• Reduction is the Gain of Elections
• E.g., a gain of electrons results in a decrease
  (reduction) in electrical charge (since electrons
  carry a negative charge)
• Metal ores are Reduced to metals (via the
  addition of electrons)metals found in ores are
  in an oxidized form relative to metals found as
  metals

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Oxidation and Reduction

• Note that oxidation and reduction are not
  necessarily complete
• E.g., movement of an electron from relatively
  close to an atoms nucleus to farther away, but
  still bonded, is also oxidation
• (and moving an electron closer is still
  reduction)
• E.g., electrons in C-H bond are closer to C than
  those in C-O bond

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Oxidation of Carbon (1/2)
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Oxidation of Carbon (2/2)
H H H-C-O H
O-H H-CO
H H-CO
H H-C-H H
OCO
This is Carbon Dioxide
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Complete Oxidation of a Hydrocarbon
CXHY (X¼Y)O2 ? XCO2 ½Y(H2O)
Energy

• Note that each Carbon gives rise to one CO2
• Note that every 2 Hydrogens gives rise to one H2O
• CO2 is the common highly Oxidized form of Carbon
• H2O is the common highly Oxidized form of
  Hydrogen
• (note also that H2O represents a reduced form of
  Oxygen)

C3H8 (32)O2 ? 3CO2 4(H2O)
Energy
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Complete Oxidation of Glucose
CXHY (X¼Y)O2 ? XCO2 ½Y(H2O)
Energy
C6H12O6 (63-3)O2 ? 6CO2 6(H2O)
Glucose is a Hexose!
C6H12O6 6O2 ? 6CO2 6(H2O)
Energy
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Oxidizing Agents (e.g., NAD)
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Oxidizing Agents (e.g., FAD)
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Oxidation and Reduction II

• Recall that both FAD and NAD can oxidize other
  molecules
• In doing so they remove two electrons and two
  protons
• In the process FAD is reduced to FADH2 and NAD
  to NADH H
• Note that two electrons two protons (I.e., 2H)
  two Hs
• (that is, neutral Hydrogen atoms)
• Note that FADH2 NADH H can be oxidized
• In the course of this oxditation they are reduced

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Reducing Agents (e.g., NADH)

• Oxidizing agents steal electrons
• In the process they are reduced
• Reducing agents donate electrons
• In the process they are oxidized

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Pop Quiz!
FADH2
So which is the Reducing agent, FAD or FADH2?
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Energy (another reminder)
Potential Energy
Kinetic Energy
Kinetic
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C H Oxidation Releases Energy
Oxidation is the movement of electrons from near
the nucleus of certain atoms (e.g., Carbon or
Hydrogen) to even closer to the nucleus of
another atom (e.g., Oxygen) The oxidation of
atoms such as carbon or hydrogen therefore can
liberate energy This liberated energy can be
harnessed
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Dehydrogenases

• Oxidation and Reduction in biological systems
  typically is catalyzed by enzymes
• Oxidation mediated by the coenzyme NAD is
  catalyzed by enzymes know as Dehydrogenases
• Note that these are de-Hydrogen-ases these are
  enzymes that catalyze the removal of Hydrogen
  atoms
• The general reaction in which NAD participates
  is
• NAD 2H 2e- ? NADH H
• which is equivalent to
• NAD 2H ? NADH H

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Dehydrogenases

• H-C-O-H NAD dehydrogenase ?
• CO NADH H dehydrogenase
• Note that the dehydrogenase is found on both
  sides of the equation it is a catalyst so is not
  used up
• 2H-C-C-H2 FAD dehydrogenase ?
• H-CC-H FADH2 dehydrogenase
• Note in both reactions the loss of two hydrogen
  atoms

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Glyceraldehyde-3-Phosphate Dehydrogenase
enzyme
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ATP Energy Currency of Cells
- - -
-
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Cellular Respiration, Overview
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ATP-Producing Pathways
Glycolysis
Cellular Respiration
Photosynthesis
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Oxidative vs. Substrate-Level Phosphorylation

• These are concepts whose distinction may not make
  sense to you until weve covered the entire
  chapter
• Substrate-Level Phosphorylation is donation of
  phosphate to ADP that is directly powered by
  making breaking bonds
• Substrate ? Product (Energy) ADP Pi ? ATP
• Oxidative Phosphorylation powered by a
  Proton-Motive Force
• There are a variety of ways to produce a
  Proton-Motive Force, all more complicated than
  Substrate-Level Phosphorylation
• These ways typically involving Electron Transport

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Glycolyis in Detail
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Glycolyis in Detail
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Glycolyis in Detail
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Glycolyis in Detail
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Glycolyis in Detail
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Outline of Glycolysis
An Enzyme- and Coenzyme-mediated catabolic pathway
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Synopsis of Glycolysis

• C6 (a.k.a., glucose) ATP ? C6-P ADP
• C6-P ATP ? P-C6-P ADP
• P-C6-P ? 2C3-P (this is the sugar-splitting step)
  
• (note the stoichiometry of all of the following
  are 2 for every one glucose)
• C3-P NAD Pi ? P-C3-P NADH H
• P-C3-P ADP ? C3-P ATP
• C3-P ADP ? C3 (a.k.a., pyruvate) ATP

This is the minimal level at which you must learn
the steps of glycolysis
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Substrate-Level Phosphorylation
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Substrate-Level Phosphorylation
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Bioenergetics
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Mitochondrial Reactions
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Pyruvate Oxidation
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Acetyl CoA
Coenzyme A
acetyl
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Oxaloacetate ? Citrate
a.k.a., Citric Acid
a.k.a., Tricarboxylic Acid
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Krebs Citric Acid Cycle
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Krebs Citric Acid Cycle
Do you see the error in this figure?

• Note that these are per Acetyl-CoA
• That means two turns of Krebs cycle per Glucose

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Krebs Citric Acid Cycle
citric acid
oxaloacetate
citrate
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Bioenergetics
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Electron Transport Chain
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Electron Transport Chain
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Electron Transport Chain
H
H
H
H
Note generation of Proton Motive Force
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Oxidative vs. Substrate-Level Phosphorylation
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Reverse-Running H Pump
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ATP Bookkeeping
glycolysis
pyruvate oxidation
Krebs cycle
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ATP Bookkeeping

• One glucose yields
• 2 ATP in glycolysis
• 2 NADH in glycolysis
• 2 NADH as pyruvate enters citric acid cycle
• 2 ATP in citric acid cycle
• 6 NADH in citric acid cycle
• 2 FADH2 in citric acid cycle

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ATP Bookkeeping
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Anaerobic Respiration
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Anaerobic Respiration
employs an inorganic molecule other than O2 as a
terminal electron acceptor.
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Glycolysis NAD Requirement
?
?
?
?
?
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Aerobic NAD Regeneration
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Anaerobic Regeneration
Fermenation Pathways
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Homolactic Acid Fermentation
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Alcoholic Fermentation
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Alcoholic Fermentation
No, These are Not Lemons!
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Mixed-Acid Fermentation (e.g., E. coli)
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Link to Next Presentation
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Acknowledgements
http//www.life.uiuc.edu/biochem/352/lecture_28/le
cture_28.ppt http//ibscore.dbs.umt.edu/bio221/dow
nloadnotes/Biol221_24a.ppt http//207.233.44.253/w
ms/reynolmj/lifesciences/lecturenote/bio3/Chap06.p
pt
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Glyceraldehyde-3-Phosphate Dehydrogenase