The document summarizes ATP synthase and oxidative phosphorylation. It describes how ATP synthase (complex V) uses the proton gradient generated by the electron transport chain to synthesize ATP from ADP and inorganic phosphate. The chemiosmotic theory explains how the proton gradient couples electron transport to ATP synthesis. Protons are pumped from the mitochondrial matrix to the intermembrane space by complexes I, III, and IV, creating an electrochemical gradient. ATP synthase allows protons to flow back into the matrix through its channel, driving the phosphorylation of ADP to ATP. Defects in this process can cause various mitochondrial diseases.

1. ATP synthase
 The enzyme complex ATP synthase
(complex V), synthesizes ATP, using the
energy of the proton gradient generated by
the electron transport chain.
 It is also called ATPase, because the
isolated enzyme also catalyzes the
hydrolysis of ATP to ADP and inorganic
phosphate.

2. ATP synthase complexes
 These complexes of proteins
are referred to as inner
membrane particles and are
attached to the inner surface of
the inner mitochondrial
membrane.
 They appear as spheres or
‘lollipop- like’ projections of
submitochondrial particles
called ‘F1’ particles, and
protrude into the mitochondrial
matrix.
 These are involved in ATP
synthesis.

3. ATP synthase
 ATP synthase is also called
F0F1-ATPase.
 This protein complex is made
up of a number of subunits (F0
subunits) and a head piece (F1).
 F0 subunits form a pore or a
channel through the membrane
while headpiece F1 sticks out
into the matrix.
 The F1 part is seen as a small
button on the inner
mitochondrial membrane.

5.  Through the pore of ATP synthase, protons
return to the matrix while the headpiece (of
ATP synthase) catalyzes the reaction
between inorganic phosphate Pi and ADP
resulting in the synthesis of ATP molecule.

6. .
The energy of electron transfer is efficiently
conserved in proton gradient
 The transfer of two electrons from NADH
through the respiratory chain to molecular
oxygen can be written as
NADH + H+ + 0.5 O2 ----- NAD+ + H2O
This net reaction is highly exergonic.
-220 kJ/mol (of NADH)
 A simiIar calculation for the oxidation of
succinate shows a smaller, but still negative,
standard free-energy change of about - 150
kJ/mol.

7. OXIDATIVE PHOSPHORYLATION
 The transfer of electrons down the electron
transport chain is energetically favored
because NADH is a strong electron donor and
molecular oxygen is an avid electron
acceptor.
 However, the flow of electrons from NADH to
oxygen does not directly result in ATP
synthesis.

8. Chemiosmotic theory (1961)
 The chemiosmotic hypothesis (also known
as the Mitchell hypothesis) explains how
the free energy generated by the transport of
electrons by the electron transport chain is
used to generate ATP from ADP + Pi

9.  Normally, large change in free energy that
occurs during electron transport could
have been dissipated as heat.
 However, this energy is very effectively
conserved by using it in the
phosphorylation of ADP to ATP. Thus, the
electron transport and phosphorylation
exist as tightly coupled processes.

11. Proton pump
 Free energy change is large enough to the
transport of protons (H+) across the inner
mitochondrial membrane from the matrix to the
intermembrane space.
 This process creates across the inner mitochondrial
membrane
 an electrical gradient (with more positive charges on the
outside of the membrane than on the inside) and
 a pH gradient (the outside of the membrane is at a lower
than the inside).
 The energy generated by this proton gradient is
sufficient to drive ATP synthesis.

12.  Thus, the proton gradient serves as the
common intermediate that couples oxidation
to phosphorylation.
 The ‘phosphorylation sites’ are actually the
sites of proton pumping.
 The proton pumping is fuelled by the
exergonic redox reaction of respiratory chain.
 Thus, ATP synthesis is caused by flow of the
protons down their electrochemical gradient.

14. Hypothesis of chemiosmotic
theory
 The chemiosmotic hypothesis proposes
that
after protons have been transferred to the
cytosolic side of the inner mitochondrial
membrane, they reenter the mitochondrial matrix
by passing through a channel in the ATP
synthase complex, resulting in the synthesis of
ATP from ADP + Pi and, at the same time,
dissipating the pH and electrical gradients.

15. Inherited defects in oxidative
phosphorylation
 Thirteen of the approximately 100 polypeptides required
for oxidative phosphorylation are coded for by
mitochondrial DNA (mtDNA) whereas the remaining
mitochondrial proteins are synthesized in the cytosol and
transported into mitochondria.
 Defects in oxidative phosphorylation are more likely a
result of alterations in mtDNA which has a mutation rate
about ten times greater than that of nuclear DNA.
 Tissues with the greatest ATP requirement (for example,
CNS, skeletal and heart muscle, kidney, and liver) are
most affected by defects in oxidative phosphorylation.

16.  Mutations in mtDNA are responsible for several diseases
 Leber's hereditary optic neuropathy, is a disease which
effects CNS
 There bilateral loss of central vision occurs as a result of
neuroretinal degeneration, including damage to the optic
nerve.
 There is a single point mutation in the polypeptide of
Complex I.
 mtDNA is maternally inherited because mitochondria from
the sperm cell do not enter the fertilized egg.

17.  Alper disease is caused by deficiency of
cytochrome oxidase.
 Myoclonic epilepsy with ragged red
fibres (MERRF) is a disease,
characterized, by uncontroIlable muscular
jerking,
 It results from defective production of
several of the proteins that require
mitochondrial tRNAs for their synthesis

18. Disorders of electron Transport chain
 Mitochondrial
encephalomyopathies are
a heterogenous group of
disorders that involve
morphological abnormalities
of muscle and brain
mitochondria.
 Leigh disease is a
mitochondrial
encephalomyopathy caused
by oxidoreductase
deficiency.

19. Mitochondria and Apoptosis
 The process of apoptosis or programmed cell death
may be initiated by the formation of pores in the
outer mitochondrial membrane.
 These pores allow cyt c to leave the intermembrane
space and enter the cytosol.
 Once in the cytosol cyt c in association with
proapoptotic factors activates a family of proteolytic
enzymes (the caspases), causing cleavage of key
proteins and resulting in morphological and
biochemical changes characteristic of apoptotic cell
death.

20. University Questions
 What is chemiosmotic theory
 A child accidentally took cyanide and was
brought to the hospital in coma. What is the
effect of this poison on mitochondril
respiration
 Describe complex V of ETC along with its two
inhibitors
 What is the role of ATP synthase in ATP
production

21.  Draw and label a diagram to illustrate the
components, organization and site specific
inhibitors of ETC
 Enumerate the components and functions
of Complex V of respiratory chain.

22. Efficiency of ETC
 Efficiency of ETC is 68% as compared to
ordinary engine which has 23%
efficiency.
 This is due to step wise oxidation of
reducing equivalents instead of direct
combustion of substrate to O2