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1. MECHANISM OF
PHOTO-PHOSPHORYLATION
Muhammad Adnan Qadar
GC University Lahore

2. PHOSPHORYLATION
Addition of a phosphate (PO4
-3 ) group to a
Protein or Organic group.
E.g., ADP + Pi
PHOTO-PHOSPHORYLATION
Process of creating ATP using a proton gradient.
Proton gradient is established by sunlight energy.

3. COMPONENTS INVOLVED IN
PHOTO-PHOSPHORYLATION
A. Sunlight
B. H+ gradient across thylakoid
C. ATP Synthase/ATP ase/CF0-CF1 Complex
D. Uncouplers (DNP, NH4
+)
E. Inhibitors (Paraquat & DMU)
F. PS I & PSII
G. Electron (e-) carriers (PQ, Cytb6f, PC etc)
• Sunlight frequency must be of 680nm-700nm range
• Proton gradient explained by
• Peter Mitchell
• G. Hinds and Andre Jagendorf
• ATP synthase mainly involved enzyme
• Uncouplers HINDERS ATP synthase function
while
• Inhibitors STOP ETC

4. CHEMIOSMOTIC THEORY
States that ‘’movement of H+ across thylakoid
from stroma to lumen down the electrochemical
gradient’’
Proposed by Peter Mitchell in 1961
IMPORTANT POINTS
• H+ gradient across thylakoid is the main source of
ATP synthesis
• Rejected by all researchers of that era
• NOBLE PRIZE was awarded upon this
afterward in 1978

5. SUPPORT TO MITCHELL
Light is not a direct requirement for ATP
synthesis but H+ gradient
G. Hinds and Andre Jagendorf
1963 experimentally proved it

6. EXPERIMENT
They put thylakoid in buffer of pH 4
Then transferred pH 4 thylakoid in buffer of
pH 8 (Kept in darkness)
Observed ATP synthesis in thylakoid.. Which
strengthened the Mitchell’s theory

7. KINDS OF PHOTO-PHOSPHORYLATION
Photo-phosphorylation takes place through;
1. ATP Synthase
2. Cyclic ETC
3. Non-Cyclic ETC

8. 1. ATP SYNTHASE
Consists of;
Hydrophillic (Coupling Factor or CF1) End
• Components
• Alpha (α3)
• Beta (β3)
• Gamma (γ)
• Sigma (δ)
• Epsilon (ε)
Hydrophobic (Coupling Factor or CF0) End
• Components
• a
• b
• b’
• C12

9. STRUCTURE

10. ATP SYNTHASE WORKING
PROTONATION:
• Takes place at pH 5
• Proton H+enters between mutual connection of a
and c subunit which results conformational
change in c subunit and it rotates
DE-PROTONATION:
• Takes place at pH 8
• Proton H+ leaves from CF1 which results
conformational change in β subunit and it OPENS
and let the ATP release

11. BINDING CHANGE MECHANISM

12. 2. CYCLIC PHOSPHORYLATION
When no reduced NADP+

13. 3. NON-CYCLIC
PHOTOPHOSPHORYLATION
When reduced NADP+ available

14. SUMMARY

15. PLANT IS THE CAUSE OF HUMAN
HABITATION ON EARTH
(Solid Quote)

16. Thank you