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Oxidative PhosphorylationMaking Cellular Energy
Joanne OellersMarch 9, 2012
Cells Make ATP by Two Fundamentally Different Mechanisms
1. Substrate-level phosphorylation in which a
phosphate group is transferred directly to ADP as
occurs in glycolysis and Krebs cycle
2. Oxidative phosphorylation in which ATP is
synthesized using energy from a proton gradient with
the help of the enzyme ATP synthase
• Organisms that metabolize food with the help of
oxygen perform oxidative phosphorylation to produce
ATP
Oxidative Phosphorylation
• Is the final step in the complete breakdown of glucose through aerobic respiration
• Is the process by which the majority of ATP is synthesized in organisms utilizing oxygen
• Operates through a mechanism proposed in 1961 by Peter D. Mitchell, the Chemiosmotic Theory of Energy Transfer
Chemiosmosis Includes Two Steps
1.The flow of electrons through the protein
complexes called electron-transfer chains driving
protons across membranes in one direction
2.An electrochemical gradient derived from those
same protons moving through the enzyme ATP
synthase in the opposite direction
Location of a Mitochondrion
MitPred. http://www.imtech.res.in/raghava/mitpred/. Accessed 3/2/12
Oxidative Phosphorylation:
• Employs the products of glycolysis, the
preparatory reaction, and the Krebs cycle
of aerobic respiration
• Brings oxygen into the equation
• Operates using concepts you already know
Oxidative Phosphorylation
Diffusion happens
A protein changes shape
when it combines with
another substance
Oxygen is an electron hog
The Electron Transport Chain
• Embedded in the mitochondrial membrane cristae
• Consists of a series of proteins that accept and
pass along electrons delivered by NADH and FADH2
• After passing through the chain, electrons
ultimately connect with oxygen (the electron hog)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Electron transport chain
Matrix
NADH
FADH2
NAD+
ATP synthesis
ATPsynthasecomplex
Cytochrome c
NADH dehydrogenase
FAD
Intermembranespace
Ubc1 cytochrom
e oxidase
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Electron transport chain
Matrix
FADH2
NAD+
H2O
ATP synthesis
ATPsynthasecomplex
Cytochrome c
NADH dehydrogenase
FAD
Intermembranespace
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NADH
U
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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e–
O22
1–2
Electron transport chain
Matrix
FADH2
NAD+
H2O
ATP synthesis
ATPsynthasecomplex
mobile carrier
electron transportcarriers in a molecularcomplex
FAD
Intermembranespace
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NADH
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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O22
1–2
Electron transport chain
Matrix
FADH2
NAD+
H2O
ATP synthesis
ATPsynthasecomplex
Cytochrome c
NADH dehydrogenase
FAD
Intermembranespace
NADH
bc1
U
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Electron transport chain
Matrix
FADH2
NAD+
H2O
ATP synthesis
ATP
ATPsynthasecomplex
ADP + P
Cytochrome c
NADH dehyrdrogenase
FAD
Intermembranespace
NADH
bc1
U
ATP Synthase is a Molecular Turbine
Thomas Meier http://www.sfb807.de/thomas-meier.html
F0
F1
Theoretical ATP Yield for Eukaryotes• The chemiosmotic model suggests that one
ATP molecule is generated for each proton
pump activated by the electron transport
chain.
• We would expect each molecule of NADH and
FADH2 to generate three and two ATP
molecules respectively.
Actual Yield is Different
1. The inner mitochondrial membrane is somewhat
leaky to protons, allowing some of them to reenter
the matrix without passing through ATP synthase.
2. The mitochondria may employ the proton gradient
generated by chemiosmosis for purposes other
than ATP synthesis, such as transporting pyruvate
into the matrix.
All Types of Cells Perform Phosphorylation
• Eukaryotic cells
o Heterotrophic
o Autotrophic
• Prokaryotic cells
Photophosphorylation
Biology, Raven et al. 9th edition. McGraw-Hill .
Photophosphorylation in a Non-sulfur Bacterium
Why Should We Try to Understand This Process?
• The generation of a proton gradient across
a membrane and chemiosmosis leading to
oxidative phosphorylation is a fundamental
way for cells to make a living
• The operation of cells is awesome and an
example of the wonder of biology
ReferencesBiology. Raven P.H., et al. 9th ed. McGraw-Hill. 2011.
Biology Junction. www.biologyjunction.com/apch09out%20cell%20respiration.doc. Accessed 3/4/12.
Jung’s Biology Blog.
http://jchoigt.wordpress.com/2010/03/04/evolutionary-perspective-on-learning-energy-metabolism/.
Accessed 3/4/12.
Hyperbaric Oxygen Info.
http://www.hyperbaric-oxygen-info.com/aerobic-cellular-respiration.html. Accessed 3/1/12.
Nobel Prize.org. http://nobelprize.org/nobel_prizes/chemistry/laureates/1978/press.html. Accessed 3/7/12.
Photobucket. http://media.photobucket.com/image/kangaroo%20rat/PurpleSkyBerry/Animals/Num.jpg?o=24
. Accessed 3/6/12.
Reference.com. http://www.reference.com/browse/electron+transport+chain. Accessed 3/4/12.
The Full Wiki. http://www.thefullwiki.org/Electron_transport_chain#Electron_transport_chains_in_bacteria.
Accessed 3/5/12.