RESPIRATION &
COUPLED
REACTIONS
THE ELECTRON TRANSPORT CHAIN
(ETC)
Coupling the oxidation of food to the
synthesis of ATP
Oxidation Is a Loss of electrons (OIL)
Reduction Is a Gain of electrons (RIG)
© 2010 Paul Billiet ODWS
Natural Electron ACCEPTORS
Pyridine nucleotides
Nicotinamide Adenine Dinucleotide (NAD)
Flavine Adenine Dinucleotide (FAD)
NAD+
+
2H+
+
2e-
Reduction
NADH + H+
Oxidation
Cytochromes Conjugate proteins which contain a haem
group.
The iron atom undergoes redox reactions
Reduction
Fe3+ + e-
Fe2+
Oxidation
NB The iron atom in the haem group of haemoglobin does not go
through a redox reaction
Haemoglobin is oxygenated or deoxygenated
© 2010 Paul Billiet ODWS
OXIDATIVE PHOSPHORYLATION





A series of REDOX REACTIONS using
electron acceptor/donor molecules
coupled to glycolysis and the Kreb's cycle
The electron acceptors/donors reduce (when
receiving electrons)
And oxidise (when losing electrons) one
another along an ELECTROCHEMICAL
GRADIENT
Each molecule in the series has a lower
REDOX POTENTIAL than the one before
© 2010 Paul Billiet ODWS
Down the chain




If this energy release is > 30.5 kJ mol-1 a mole of
ATP can be synthesised from ADP by a coupled
reaction
The first molecule in the series is NAD (or FAD),
a COENZYME of various DEHYDROGENASE
enzymes
[NAD (oxidised)  NADH + H+ (reduced)]
Next come a series of iron containing proteins
called CYTOCHROMES
© 2010 Paul Billiet ODWS
NAD+
NADH + H+
+ve
FAD
FADH2
2e-
G=- 51 kJ
Redox potential
Flavoprotein/Cytochrome b
 G=- 38.5 kJ
2e-
Cytochrome c
Cytochrome a.a3
-ve
 G=- 84.5 kJ
2e1/
2O2
H2O
© 2010 Paul Billiet ODWS
Reaction co-ordinate
+ 2H+
The electron transport chain
Electrons are produced by splitting hydrogen
atoms taken from the food molecules
(H  H+ + e-) by dehydrogenases
The last electron acceptor in the series is
OXYGEN
Thus at the end of the ETC:
2H+ + 2e- + 1/2O2  H2O
© 2010 Paul Billiet ODWS
The location of the ETC
The mitochondrial inner membrane of
eukaryotes(the plasma membrane of
prokaryotes)
 Surface area increased by CRISTAE
Numbers of cristae = activity of cell
e.g. Liver cell 40 m2 g-1 mitochondria
Heart muscle 200 to 250 m2 g-1
mitochondria

© 2010 Paul Billiet ODWS
The importance of the inner
membrane
Mouse cardiac muscle
Image Credit: Open University S Hurry (1965) Murray
Insect flight muscle x 42 000
Image Credit: Open University S Hurry (1965) Murray
Outer membrane
Inner membrane
eH+
H+
The Mechanism
of Oxidative
phosphorylation:
THE
CHEMIOSMOTIC
PUMP
H+
MATRIX
O2
2H2O
ADP + Pi
H+
ATP
ATP
synthetase
Intermembrane space
© 2010 Paul Billiet ODWS
The Mechanism: THE
CHEMIOSMOTIC PUMP
The ETC creates a concentration gradient
by pumping H+ out of the mitochondrial
inner matrix
 As these H+ diffuse back into the matrix
across the inner membrane they drive
ATP synthesis

© 2010 Paul Billiet ODWS
THE CHEMIOSMOTIC PUMP IN
CHLOROPLASTS
X 22 000
Image Credit: Open University S Hurry (1965) Murray
X 80 000 Image Credit: Open University S Hurry (1965) Murray
Photophosphorylation
2H+
NADP+
Stroma
2H+
2e-
2e2H+ +
1/ O
2 2
H2O
1/
NADPH+
+ H+
2O2
2e-
2H+
Thylakoid
space
2H+
2H+
Thylakoid
membrane
ATP
synthetase
ADP + Pi
© 2010 Paul Billiet ODWS
2H+
ATP