3. INTRODUCTION
Respiration is the oxidative breakdown of organic
compound to release energy.
Organic compounds:
LIPIDS PROTEINS CARBOHYDRATES
Main aim of these various metabolic reactions is to
produce ATP.
But how is ATP produced?
3
4. NADH₂ AND FADH₂
All the metabolic pathways lead to the production of
NADH₂ AND FADH₂ molecules. These compounds are
highly reduced or energy rich.
These molecules are oxidized via the ETC chain.
Oxidation refers to the loss of electrons or hydrogen
atoms.
The oxidation process releases large amount of
negative free energy which then drives the synthesis of
ATP from ADP. (C/a Oxidative phosphorylation).
BUT THE PROCESS IS NOT SO SIMPLE!
4
5. Role of NAD/ NADP linked dehydrogenases :
(removes two electrons from its substrate)
Hydride ion(:H) proton(H⁺)
(transferred to NAD⁺ or NADP⁺)
Reduced subs + NAD⁺ oxidised subs + NADH
Reduced subs + NADP⁺ oxidised subs + NADPH
Example:
αketo glutarate+ CoA + NAD⁺ Succinly CoA + CO₂ +
NADH + H⁺
NADH₂
5
6. FADH₂
CONCEPT OF FLAVOPROTEINS :
The FMN and FAD molecules are linked to
flavoproteins.( to the active site)
The reduction potential of these molecules depends
on the interactions with local sites on the protein.
Unlike NAD or NADP molecule, can accept one or two
electrons, thus :
FMN/FAD + e⁻ FMNH•/FADH•
OR
FMN/FAD + 2e⁻ FMNH₂/FADH₂
6
7. LOCATION OF
ETC
Outer membrane
Inner membrane
(ETC)
Matrix
Permeability of the
two membranes
Contents of the matrix
7
8. COMPLEXES OF ETC
The ETC consists of five separate protein complexes:
Complex I , II, III, IV and V.
The complexes I, II, III and IV are involved in
transportation of electrons to molecular oxygen.
The complex V is involved in the synthesis of ATP.
Each complex consists of certain prosthetic groups
which are the ‘electron carriers’ in that respective
complex.
The electrons are sequentially passed from complex I
to V.
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10. COMPLEX I
Also called as NADH Dehydrogenase.
PROSTHETIC GROUPS: 1.) FMN
2.) FE-S center ( atleast six)
IRON-SULFUR centers: in these centers, the iron is
present in association with inorganic sulfur atoms or
with the sulfur atoms of cysteine residues of the
protein.
These centers can range from simple structures to
complex i.e one Fe atom cordinated to 4Cys residues
Or they can be complex like 2 Fe- 2S or 4Fe- 4S
centers.
10
12. PATHWAY FOR TRANSFER OF ELECTRON
THROUGH COMPLEX I
Intermembrane space
(P side)
Matrix
( N side)
At the end there is net transfer of four protons from the matrix to
intermembrane space.
12
13. COMPLEX II
Succinate
dehydrogenase complex
Has 4 subunits
A: binding site for
substrate and FAD
B: 3 Fe-S centers
C:binding site for
ubiquinone.
D: contains heme b .
(Not involved in electron
transfer).
Subunits A and B are
present towards matrix and
subunits C and D are
embedded in membrane.
Subs binding site Sub A
FAD
Fe-S
Heme b
Ubiquinone
(purple)
Sub B
(brown)
Sub D
(blue)
Sub C
(green)
13
14. PATHWAY OF ELECTRON TRANSFER
THROUGH COMPLEX II
No transfer of protons from the matrix to intermembrane space.
14
15. UBIQUINONE
Ubiquinone is a quinone derivative with a long
hydrophobic isoprenoid tale.
It can accept one electron to form the semiquinone
form ( QH•) or it can accept two electron to form the
ubiquinol (QH₂).
Besides Complexes I and II , other sources donates
electrons directly to ubiquinone.
15
16. PATHWAYS OF
ELECTRON FLOW
TO UBIQUINONE
Glycerol 3 phosphate
genertaed during
glycolysis from DHAP
and also from fatty acids
degradation.
The fatty acyl CoA is
generated during β
oxidation of fatty acids.
ETF: Electron
Transport Flavoprotein
16
17. CYTOCHROMES
The next complexes i.e. complex III and complex IV are
cytochromes.
Each cytochrome consists of a heme group i.e. iron
encaged in a porphyrin ring .
The Iron of heme group is readily convertible to Fe⁺² from
Fe⁺³ state.
The cytochrome a has heme a
Cytochrome b has heme b
Cytochrome c has heme c
Besides this each cytochrome differs in their light
absorption spectra.
17
19. COMPLEX III
Also called as cyt bc1
complex.
Has cyt b and cyt c.
Cyt b has heme b
Cyt c has heme c
Besides these reiske
iron sulfur centers are
present.( iron attached
to histidine residues)
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20. FLOW OF ELECTRON VIA COMPLEX III
Follows a special Q cycle.
At the end there is net transfer of four protons from the matrix to
intermembrane space.
20
21. COMPLEX IV
Also c/a cyt a a₃
complex.
Has 13 subunits.
Subunit I: has heme a,
heme a₃, and Cu ion B.
Subunit II: has 2 Cu
ions , forms binuclear
centre.
Subunit III: role not
clear but important for
functioning of this
complex.
21
23. In actively respiring mitochondria the measured
electrical gradient is 0.15 to 0.20 volts
The pH difference is 0.75 units.
The free energy change for pumping one proton is
20kJ/mol of H⁺, thus for pumping ten protons the
energy released is 200kJ/mol
ATP formation requires only 50kJ of energy.
23
24. COMPLEX V
Also c/a ATP synthase.
F₁ particle- 9 subunits.
F₀ particle : 3 subunits.
24
25. α
ADP
β ADP
α empty
β empty
β ATP
α ATP
25
β subunits differ in their conformations
