Coupling factors and mechanism of atp synthesis and
1. COUPLING FACTORS AND MECHANISM OF ATP
SYNTHESIS AND CONCEPT OF QUANTUM YIELD
PRESENTED BY,
P S KIRAN
(Msc.plant physiology
student)
2. LIGHT REACTION V/S DARK REACTION
• What differentiate between light and dark reactions?
• Does dark reaction completely independent of light?
• What happens in light reaction?
• Cyclic and Non cyclic photophosphorylation
• What is the difference between NADPH and NADH2?
• How the assimilatory powers are formed in light reaction?
• Coupling factors and mechanism of ATP synthesis
• Concept of quantum yield
4. DIFFERENCE BETWEEN LIGHT AND DARK REACTION
LIGHT REACTION
• Light reaction only takes place in the
presence of light
• Takes place in grana
• Also called photo-chemical phase
• Oxidation of water and production of
“assimilatory powers”
DARK REACTION
• Takes place with the presence or
absence of sunlight
• Takes place in stroma
• Also called as biosynthetic phase
• Reduction of co2 to carbohydrate
using the “assimilatory powers”
5. DOES DARK REACTION IS COMPLETELY
INDEPENDENT OF LIGHT?
• This is a misnomer that light reaction occurs in morning(presence of sunlight) and
dark reaction occurs in the night(absence of sunlight)
• Light reaction and dark reaction occurs spontaneously i.e , one after the other
• Four enzymes in dark reaction are indirectly dependent (activated) on light
a)Ribulose 5-phosphate kinase
b)Fructose 1,6-bisphosphatase
c)Sedoheptulose 1,7-bisphosphatase
d)Glyceraldehyde 3-phosphate dehydrogenase
6. WHAT HAPPENS IN LIGHT REACTION?
• Light dependant phase of photosynthesis in which ATP and NADPH are formed in
the presence of light
• Consists of following steps:
a) light absorption
b) water splitting
c)oxygen release
d)formation of high energy chemical intermediates (ATP & NADPH)
7. LIGHT ABSORPTION
Chl + h 𝜗 → Chl*
Role of photosystems I and II (PSI and PSII)
Light absorbed by PSII PSII* ETC (pheophytin,PQ,Cyt b6f
complex) PSI PSI*
PSII-680nm & PSI-700nm
PSI present in stroma lamellae and non appressed region of grana
whereas PSII present in appressed region of grana lamella
Photosystem I produces a strong reductant, capable of
reducing NADP+, and a weak oxidant
Photosystem II produces a very strong oxidant, capable of oxidizing water,
and a weaker reductant than the one produced by photosystem I.
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9. WATER SPLITTING
• Complex for splitting of water present in inner side of thylakoid membrane
attached to PSII
• H+ ions , e- and oxygen is liberated on photolysis of water
• PSII is essential for photolysis of water to occur
• H2O 2H+ + 2e- + O2
10. OXYGEN RELEASE
• Oxygen is liberated from splitting of water and not from carbon dioxide
• Oxygen produced as a by product in splitting of water is liberated in the lumen of
the thylakoid which then diffuses into the stroma
11. FORMATION OF ASSIMILATORY POWERS
• ATP and NADPH are called as the assimilatory powers of light reaction which is
used as reducing agent in carbon fixation in dark reaction
• ATP and NADPH is formed in non cyclic photophosphorylation whereas in cyclic
photophosphorylation only ATP is formed
• NADP reductase enzyme is present in the outer membrane of thylakoid
• H+ ions for reduction of NADP comes from stroma
12. CYCLIC AND NON CYCLIC
PHOTOPHOSPHORYLATION
CYCLIC PHOTOPHOSPHORYLATION
• PSI is functional
• Only ATP is formed
• Photolysis of water is absent
• Mostly occurs in stroma lamella
• Found dominant in photosynthetic
bacteria
NON CYCLIC
PHOTOPHOSPHORYLATION
• Both PSI and PSII are functional
• ATP and NADPH is formed
• Photolysis of water is present
• Occurs mostly in grana lamella
• Dominant in green plants
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14. NADPH AND NADH2
NADPH
• Occurs as an assimilatory power in
photosynthetic light reaction
• Mostly involved in anabolic processes
• Acts as a strong reducing agent for
reducing carbon dioxide to glucose
NADH2
• Occurs as a proton carrier in
respiration
• Mostly involved in catabolic
processes
• It liberates ATP when required and
also act as a proton carrier in
mitochondrial ETC
15. PROTON TRANSPORT AND ATP
SYNTHESIS IN THE CHLOROPLAST
• In the preceding sections we learned how captured light energy is used to reduce
NADP+ to NADPH. Another fraction of the captured light energy is used for light-
dependent ATP synthesis, which is known as photophosphorylation
• It is now widely accepted that photo phosphorylation works via the chemiosmotic
mechanism, first proposed in the 1960s by Peter Mitchell.
• Differences in chemical potential of any molecular species whose concentrations are
not the same on opposite sides of a membrane provide such a source of energy.
• The direction of proton translocation is such that the stroma becomes more alkaline
(fewer H+ ions) and the lumen becomes more acidic (more H+ ions) as a result of
electron transport
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17. COUPLING FACTORS AND MECHANISM OF ATP
SYNTHESIS
• Chemiosmotic hypothesis by Peter Mitchell
• ATP production driven by proton gradient difference
• High concentration of H+ in lumen and low concentration of H+ in stroma creates
a gradient and proton is transported from lumen to stroma through CF0-CF1
complex
• CF0 is an integral protein present in the outer thylakoid membrane which helps in
the facilitated diffusion of H+ from lumen to stroma
• CF1 is the ATP synthase complex where iP combines with ADP to form ATP in the
presence of high energy H+ ions
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28. CONCEPT OF QUANTUM YIELD
• The number of photons/quanta required to release one molecule of oxygen in
photosynthesis is called as quantum requirement . On the other hand, number
of oxygen molecule released per photon of light in photosynthesis is called as
quantum yield . The quantum yield is always in fraction of one
29. RED DROP AND EMERSON ENHANCEMENT EFFECT
• Sudden fall in photosynthesis yield observed beyond red region of visible
spectrum is called Red drop/Emerson’s first effect
• The increase in photosynthetic activity by combined effect of short and long
wavelengths of light is called Emerson’s enhancement effect/second effect
