Oxidative Phosphorylation Making Cellular Energy Joanne Oellers March 9, 2012.

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.

H+

H+

H+

H+

H+

H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

e–

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.

H+

H+

H+H+

H+

H+

H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

e–

O22

1–2

Electron transport chain

Matrix

FADH2

NAD+

H2O

ATP synthesis

ATPsynthasecomplex

Cytochrome c

NADH dehydrogenase

FAD

Intermembranespace

H+

H+

H+

NADH

U

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

H+

H+

H+H+

H+

H+

H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

e–

O22

1–2

Electron transport chain

Matrix

FADH2

NAD+

H2O

ATP synthesis

ATPsynthasecomplex

mobile carrier

electron transportcarriers in a molecularcomplex

FAD

Intermembranespace

H+

H+

H+

NADH

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

H+

H+

H+

H+H+

H+

H+

H+H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

e–

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.

H+

H+

H+

H+H+

H+

H+

H+H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

e–

O22

1–2

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.