Respiration – a process by which cells
derive energy with a controlled reaction
between H+ and O2; the end product being
Aerobic organisms are able to capture a
far greater proportion of the available free
energy of respiratory substrates than
• The objective of respiration is to produce
• Energy is released from oxidation
reactions in the form of electrons
• Electrons are shuttled by electron carriers
(e.g. NAD+) to an electron transport chain
• Electron energy is converted to ATP in the
electron transport chain
• Metabolism is the sum of the chemical
reactions in an organism.
• Catabolism is the energy-releasing
• Anabolism is the energy-using processes.
• Catabolism provides the building blocks
and energy for anabolism.
ATP couples energy between
CATABOLISM AND ANABOLISM
Energy available for work
& chemical synthesis (e.g.
ADP + Pi
Energy from food (fuel
molecules) or from
• Oxidative phosphorylation is the process by
which the energy stored in NADH and FADH2
is used to produce ATP.
• A. Oxidation step: electron transport chain
NADH + H+ + O2
NAD+ + H2O
FADH2 + O2
FAD + H2O
B. Phosphorylation step
ADP + Pi
• Mitochondria, have been
termed the "powerhouses"
of the cell since the final
energy release takes place
in the mitochondria only.
• Mitochondria have an
outer membrane that is
permeable to most
metabolites, an inner
membrane that is
permeable, enclosing a
matrix within .
• The outer membrane is characterized by the presence
of various enzymes, including acyl-CoA synthetase
and glycerol phosphate dehydrogenase.
• Adenylyl kinase and creatine kinase are found in the
• The phospholipid cardiolipin is concentrated in the
inner membrane together with the enzymes of the
respiratory chain, ATP synthase and various
• The matrix encloses the enzymes of TCA cycle, beta
oxidation and pyruvate dehydrogenase complex.
The electron transport chain is series of
protein complexes embedded in
This chain is consist of 4 complexes and
4 complexes are :
3. Cytochrome b-c
4. Cytochrome oxidase
Electrons are come from electron carriers and
they travel through the electron transport chain
where the electrons final destination is oxygen
which will help to reduce Oxygen to form water.
So oxygen is known as final acceptor.
Electrons captured from donor molecules are
transferred through 4 complexes.
NADH-coenzyme Q oxidoreductase, also known as
NADH dehydrogenase or complex I, is the first protein in
the electron transport chain
• In Complex I, In which NADH dehydrogenase oxidized
to NAD+H+,this process obtain two electrons which
will first given to FMN(flavin mononucleotide) from
here the electrons are transfered one at a time
through a series of iron sulfur center than 2 electrons
create a proton gradient which bring 2 hydrogen ions
from the matrix and bound to ubiquinone and as a
biase ubiquinone it will reduced to ubiquinol(QH2).
• Complex I can transfer 4 protons from the matrix inner
membrane space.It will be seen that transfer of four
protons in to inner membrane space is equivalent to
formation of one ATP molecule.
Succinate-Q oxidoreductase , also known as
complex 2 or succinate dehydrogenase,(from the
citric acid cycle)is a second entry point to the
electron transport chain.
It contains FAD(Flavin adenine dinucleotide)
and Fe-S centers; it lacks proton pump activity.
It oxidizes succinate to fumarate and reduces
ubiquinone. The two hydrogen atoms are first
taken up by FAD to form FADH2 then passed
through a series of iron sulfur centers and
passed to ubquinone.
As this reaction releases less energy than the
oxidation of NADH, complex II does not
transport protons across the membrane and
does not contribute to the proton gradient.
For this reason, whereas transfer of two
hydrogen from NADH+H+ to coenzyme Q by
the complex 1 results in formation of one
ATP,the transfer of two H atoms from FADH2
to coenzyme Q does not give rise to any ATP.
• Coenzymes Q ubiquinone flows to the inner membrane
• its purpose is to carry electron through different
complexes because it is a mobile protein where the
complexes are stationary coenzymes travel to the inner
membrane with 2 electrons.It would not associate with
complex 2 but it would associate with complex 3.
Cytochrome b-c complex also called
cytochrome c oxireductase
Complex 3 has a few important sub unit or 3
1. Iron sulphr (Fe-S) protein
2. Cytochrome b
3. Cytochrome c
• Cytochromes are protein containing heme
• When Electrons are donated from NADH to
NADH dehydrogenase, a large protein complex
that pumps protons across the inner
• Then, electrons are transported to the
coenzyme Q (Q), also termed ubiquinon; then
ubiquinon travel to the inner membrane and
associate with the subunit of complex 3.
In complex 3 cytochrome c is not a part of any
enzyme complex, is freely soluble and occurs in
the inter membrane space
Cytochrome c is also called mobile protein
because it travel to the inter membrane space
and attached or bind to the complex 4
The final step of ETC is the reduction of
molecular oxygen by electrons derived from
Complex 4 consist of 3 important sub unit
1. Subunit 1 has two heme group a and a3
2. Subunit 2 contains two Cu ions
3. Subunit 3 is essential for the activity of
The cytochrome oxidase complexes then
transfer electrons from cytochrome c to
oxygen, the terminal electron acceptor, and
water is formed as the product.
Cytochrome oxidase also pumps 2 protons
across the membrane.
The transfer of protons generates a proton
motive force across the membrane of the
Electrons are transported between all these
complexes and where will rise at oxygen so oxygen is
final electron aceptor.
These electrons are come from 1NADH and so now if
we calculate all the protons pumped from 1 NADH to
all the complexs.
Complex 1 = 4 protons
Complex 3 = 4 protons
Complex 4 = 2 protons
These 10 hydrogen ion it would go through the ATP
synthase to produce ATP
• The chemiosmotic theory was developed by the British
biochemist, Peter Mitchell which explain the mechanism of ATP
• According to this theory, the tranfer of electrons down an
electron transport system through a series of oxidationreduction reactions releases energy .As electrons are
transferred along the electron Transport chain from electron
donor to electron acceptor in the inner mitochondrial
membrane,free energy is released. This energy allows certain
carriers in the chain to transport hydrogen ions (protons) which
thus contains a higher concentration of protons than the matrix.
This creates an electrochemical gradient across the inner
membrane. The energized state of the membrane as a result of
this charge separation is called proton motive force or PMF.
• This proton motive force provides the energy
necessary for enzymes called ATP synthases, to
catalyze the synthesis of ATP from ADP and
• This generation of ATP occurs as the protons across
the membrane through the ATP synthase complexes
re-enter the matrix of the mitochondria. As the
protons move down the concentration gradient
through the ATP synthase, the energy released
causes the rotor (F0) and stalk of the ATP synthase to
rotate. The mechanical energy from this rotation is
converted into chemical energy as phosphate is added
to ADP to form ATP in the catalytic head (F1 domain)
The Generation of ATP
• ATP is generated by the phosphorylation of
The ATP synthase has
two distinct subunits:
The transmembrane F0
subunit, which contains a
protein channel for the flow
The F1 subunit, which
protrudes into the matrix
space and catalyzes the
synthesis of ATP from ADP
and inorganic phosphate
ATP synthase is embedded in the
inner membrane, together with the
respiratory chain complexes .
Several subunits of the protein
form a ball-like shape arranged
around an axis known as F1, which
projects into the matrix and
contains the phosphorylation
F1 is attached to a membrane
protein complex known as
F0, which also consists of several
F0 spans the membrane and forms
The flow of protons through F0 causes it to
rotate, driving the production of ATP in the F1
A portion of the F1 subunit termed the stalk
links the two subunits.
As protons flow through the channel in the F0
subunit, they cause the embedded stalk to
rotate in the stationary F1 subunit, thereby
converting the energy of the electrochemical
gradient into mechanical energy.
• As the stalk rotates in one
direction, it induces
conformational changes in the
proteins of the F1
subunit, which, in turn, catalyze
the synthesis of ATP - thereby
converting the mechanical
energy of stalk rotation to
chemical bond energy.
Approximately 4 protons must
pass through the ATP
synthase complex for one ATP
molecule to be synthesized
• The hydrogen concentration is much greater
in the inter membrane space than in the
matrix, thus generating an electrochemical
proton gradient. This gradient drives protons
back across the inner membrane through the
ATP synthase (shown in gray) that catalyzes
the synthesis of ATP from ADP and inorganic