Peter Mitchell
and the Chemiosmotic
Theory
Who is Peter Mitchell?
• Was born 29th September, 1920
and died 10th April 1992.
• Was a British biochemist and a
Fellow of the Royal Society.
• He went to Queen's College,
Taunton, and
Jesus College,
Cambridge where he studied
the
Natural
Sciences
and
specialized in biochemistry.
• In 1978 he won the Nobel Prize in
Chemistry “for his contribution to
the understanding of biological
energy transfer through the
formulation of the chemiosmotic
theory.”
What We Know So Far…
• In 1945, Albert Lehninger established the
existence of a link between the Krebs cycle
and the catabolism of fatty acids In he cell.
• In 1949, Morris Friedkin, together with his PhD
supervisor, Albert Lehninger , showed the
existence of a connection between
different metabolic pathways for coenzyme
NADH to oxygen as a source of energy in
oxidative phosphorylation.
Introduction
• After the Krebs cycle was found, biochemists began to
used Hans Krebs’ method of finding the steps of the
Krebs cycle to find the steps to make ATP.
• In the late 1940s, scientists who studied membrane
transport were separate into two distinct groups: those
who studied the membrane and those who studied
proteins, enzymes, and reactions they catalyzed.
• As a biochemistry graduate student at Cambridge
University in that time period, Mitchell began to study
membranes Mitchell thought of membrane transport as
both a physical phenomenon and a chemical reaction
using energy where the chemical reaction changed
reactants on one side of the membrane to products on
the other side of the membrane.
The Experimental
Process
• Experimented on bacteria and studied how they
transported various compounds across their membranes.
• Concluded that chemical reactions occurred in 3-D
spaces.
• Began to see energy-and-membrane transport process
in reverse.
• A grad student found that the transport of a certain
sugar in bacteria correlated with the movement of a H+
ion.
• Shifted his efforts from working on bacteria to working on
eukaryotic mitochondria as well as the membranes of
plant cell chloroplasts.
The Experimental
Process (Cont’d.)
• In 1965, Mitchell was asked to present his
chemiosmotic ideas at a conference.
• Learned how to measure proton concentration
(pH) in the solution outside the mitochondria.
• Significant Issue: how electrons could carry
protons across the membrane while moving
down energy levels.
• He continually revised and changed his ideas.
He sought advice and peer review.
The Breakthrough
• Cornell University Student André Jagendorf a graduate
student had measured the proton changes due to electron
transport in chloroplasts. In order to make sure this wasn’t a
coincidence, they set up and experiment where an
imbalance of protons was artificially created in order to view
the possible effects.
• First they incubated chloroplasts in acid baths and allowed
protons to saturate the solution both inside and outside the
chloroplast membrane. Then, they put the chloroplasts in a
solution with a lower concentration of protons, which created
an imbalance of protons across the chloroplast membrane,
and thus, produced ATP.
• This experiment was conducted in the dark so that the
chloroplasts wouldn’t use light energy. It was concluded that
the induced proton imbalance must have made the ATP,
mimicking the real life situation in chloroplasts when light is
present.
The Independent and
Dependent Variables
Independent Variable
The acid solution
Dependent Variable
The ATP (whether or not
it was produced)
In The End…
• Peter Mitchell was the sole recipient of the Nobel
Prize for Chemistry in 1978, in recognition of “his
predominant contribution towards establishing the
validity of the chemiosmotic hypothesis, and ipso
facto, the long struggle to convince an initially
hostile establishment.”
• The chemiosmotic theory is now generally
accepted as a fundamental principle in
biogenetics and now provides a rational basis on
future work on the details of oxidative
phosphorylation.
References
•
•
•
•
•
Allchin, Douglas. "Peter Mitchell & How Cells Make
ATP."http://www1.umn.edu/ships/db/mitchell.pdf. University of Minnesota
- Twin Cities, n.d. Web. 24 Oct 2011.
<http://www1.umn.edu/ships/db/mitchell.pdf>.
Crofts, Anthony. "Peter Mitchell and The Chemiosmotic Hypothesis."Life
Sciences -University of Illinois at Urbana-Champaign. University of Illinois at
Urbana-Champaign, 1996. Web. 23 Oct 2011.
http://www.life.illinois.edu/crofts/bioph354/mitchell.html
"Functions of NAD (Nicotinamide adenine dinucleotide)
."Nangluongsinhhoc. Blogger, 2011. Web. 23 Oct 2011.
<http://nangluongsinhhoc2011.blogspot.com/2011/04/functions-of-nadnicotinamide-adenine.html>.
"Press Release: The 1978 Nobel Prize in Chemistry". Nobelprize.org. 24 Oct
2011.
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1978/press.h
tml
Wikipedia, . "Peter D. Mitchell."Wikipedia. Wikimedia Foundation, Inc.,
24th September 2011. Web. 23 Oct 2011.
<http://en.wikipedia.org/wiki/Peter_D._Mitchell>.