electron transport chain in photosynthesis

1. ELECTRON TRANSPORT SYSTEM-
OXIDATIVE PHOSPHORYLATION
DONE BY,
P. MEENALOKSHINI
II MSC BIOCHEMISTRY

2. Respiration is a biological oxidation and this can be
represented as:
C6H12O6 + 6O2 6H2O + 6CO2 + 686K Cal
Oxidative phosphorylation is the process occuring in
mitochondria in which respiration is coupled to the
generation of the high energy compound, ATP.

3. -- NADH: oxidoreductase
NADH + H+ + UQ NAD+ + UQH2
-- Succinate : Ubiquinone Oxidoreductase
Succinate + UQ Fumarate + UQH2
–Dihydro ubiquinone : cytochromeC
oxidoreductase
UQH2 + 2 ferri cyt C UQ + 2 Ferro cyt C + H+
– Cytochrome C : oxygen oxidoreductase
2 Ferro cytochrome C + 2 H+ + ½ O2 2 Ferri cyt + H2O

4. Devlin, Biochemistry

5. • It consists of flavoprotein FMN and is
associated with non-heme iron sulphur protein.
This complex is responsible for passing
electrons from mitochondrial NADH/NADPH
to Ubiquinone.
• In plants an additional external DHase
complex is present which can oxidise cytosolic
NADH.

6. • It consists of a flavoprotein FAD in its
prosthetic group and is associated with non
iron sulphur protein.
• This complex serves electrons from succinic
acid , which is oxidised in kreb’s cycle to form
fumaric acid and passes them to Ubiquinone.

7. • It consists of two form of cytochrome B (cyt
b562 & cyt b566) non heme iron sulphur
protein and cyt C1.
• This complex receives electron from UQH2
and passes them to cytochrome C .

8. • It consists of cytochrome a & a3. The enzyme of this
complex contains copper ions in the form of 2 copper
centers CuA & CuB.
• This complex receives electrons from cytochrome C
and passes them to H2O2.
• Two protons are needed and water molecule is
formed.
• The transfer of electrons from reduced co-enzymes
NADH to O2 via Complex I to IV is coupled with the
synthesis of ATP from ADP and Pi, which is called as
oxidative phosphorylation.

9. • The inner mitochondrial membrane is
impermeable to NADH+ + H+. Therefore it
cannot pass directly into the mitochondria to
be oxidized. Two shuttles serves to transport
reducing equivalents from NADH+ + H+ in
cytosol to the ETC in mitochondria.
• Glycerol 3- phosphate shuttle
• Malate - aspartate shuttle

10. • It is secondary mechanism for transport of
reducing equivalents from cytosolic NADH +
H+ into the mitochondrian to be oxidized via
the ETC.

11. • It is the movement of reducing equivalents
from the cytoplasm to the mitochondria. It
occurs in 2 phases:
Phase A
Cytoplasmic malate DHase reduces oxaloacetate
to malate while oxidising NADH + H+ to
NAD+.
Malate is transported interior of mitochondria.
Inside , it is oxidized to Oxaloacetate by M
MDH, giving rise to NADH + H+.
NADH + H+ is oxidized in ETC giving 3 ATP.

12. Phase B
Oxaloacetate inside mitochondrian
aspartate by transamination , amino
group denoted by glutamate
a ketoglutarate. This transamination
occurs by mito GOT.
Aspartate and a keto glutarate leaves
mitochondria & enters cytosol.
In cytoplasm, asp oxaloacetate
and a ketoglutarate glutamate by
transamination by cytoplasmic GOT.
Glutamate enters into mitochondria and
the oxaloacetate begins a new turn of
the cycle.

14. • Any molecule capable of accepting 1/ 2
electrons from 1 molecule and donating to
another in the process of electron transport.
Protein electron carriers Prosthetic group
Flavoprotein FMN
Iron sulphur protein Iron & sulphur
Cytochromes Heme group

15. Non heme iron-sulphur proteins
Fe-s, Fe2S2,Fe3S4 Copper proteins
Transfer of 1 electron involving
Cu+ and Cu++ odidation states.
Iron sulphur protein
Transfer of 1 electron from FE2+
and Fe3+ oxidation states. Cytochromes
The heme iron is involved
in 1electron transfer.
Cyt b,c1,a,a3 are part of
large membrane integral
protein complexes.Ubiquinone
It is lipid soluble electron
carrier. The only carrier not
bound to a protein.

16. Matrix
H+
+ NADH NAD+
+ 2H+
2H+
+ ½ O2 H2O
2e
– –
I Q III IV
+ +
4H+
4H+
2H+
Intermembrane Space
cyt c 3H+
F1
Fo
ADP + Pi ATP
The Chemiosmotic Theory of oxidative phosphorylation,
for which Peter Mitchell received the Nobel prize:
Coupling of ATP synthesis to respiration is indirect, via
a H+ electrochemical gradient.

17. Chemiosmotic theory
proposed by Peter Mitchell-
-The transport of protons
from matrix to
intermembrane space is
accompanied by the
generation of a proton
gradient across the
membrane.
Protons (H+) accumulate
intermembrane space creating
an electrochemical potential
difference, proton gradient
or electrochemical gradient.
This proton motive force
(PMF) drives the synthesis of
ATP by ATP synthase
complex.