light dependent reactions

where do protons accumulate in chloroplast

thylakoid interior

electron carriers in photophosphorylation

• platiquinone

• platocyanin

• ferredoxin

what is the reduced form of plastoquinone

platoquinol

proton gradient of chloroplast

• lower conc in stroma

• higher conc in thylakoid lumen

• passes through chloroiplast atp synthase

what pigments are found in the photosystems

• chlorpphyll a and b

• carotenoids (reflect red and yellow - orange )

what connects psii and psi

cytochrome bf complex

where is the special pair of chlorpohyll molecules found

• reaction centre

• active site of photosystem

what happens after excitation of P680*

• electrons transferred to pheophytin

• then plastoquinone at site Qa (fixed)

• to plastoquinone at site Qb (mobile)

how is plastoquinone reduced to plastoquniol

• second electron reduces mobile plastoquinone

oxygen evolving center

• water oxidising enzyme

• water molecule bind to calcium ion and manganese ion

• 4 manganese ions for every calcium

tyrosine residue

• facilitates oxygen transfer from P680 to reach chlorophyll residues

photophosphorylation

• electron tranfer from psii to plastoquinone

• then cytochrome bf

• then plastocyanin

• then psi

• then phyloquinone

• then iron clusters

• then ferrodoxin

• then nadp reductase

resonance energy transfer

• energy released excites electron from neighbouring pigment

• energy passes from one pigment to the next

photoinduced charge separation

• electron transfer from one chlorophyll molecule to another

• only happens in special pair

what can happen when electrons are excited from ground state to excited state

• returns to ground - heat or fluorescence released

• resonance energy transfer

• photoinduced charge separation

chlorophyll a and b structure

• contains cyclic tetrapyrrole

• planar structure (delocalisation of electrons)

• mg2+ bound to centre

• one pyrrole ring is reduced

• highly hydrophobic chain

plastoquinone

• lipid soluble electron carrier

• similar structure to ubiquinone

• chain is hydrophobic so can travel through lipid membrane

reduction of plastoquinone

• two electrons needed one by one

• transfer of two electrons and two protons from stroma by cytochrome bf complex

• this happens twice to generate one oxygen, so requires 2 molecules of water

• 4 protons are released

plastocyanin

• blue copper proetin

• soluble in thylakoid lumen

• reduced at copper atom

how many molecules of plastocyanin needed to oxidise plastoquinol

• 2

what agent is plastocyanin

oxidising

what happens after excitation of P700 in PSI

• electron transferrred to chlorophyll a0

• then to phyloquinone

• then to 3-iron sulphur clusters

• then ferredoxin

where are electrons finally transferred from photosystem i p700*?

ferredoxin

how does ionised p700* recover?

electrons from plastocyanin

iron sulphur clusters

• contain cysteine residues

• each atom of iron is surrounded by 4 atoms of sulphur

• creates cubic structure

ferredoxin NADP+ reductase

• catalyses transfer of electrons from ferredoxin to nadp+

• creates nadph

• semiquinone formed as intermediate

z-scheme

• electron transfer to cofactors is energetically favorable

• electron flow from water to nadph is endergonic process - requires free energy

• free energy from photons of light at psii (p680) and psi (p700)

are p680* and p700* good oxidising agents or reducing agents?

reducing agents

chlorplast ATP synthase

• structure with knob (CF1) and stalk (CF0)

• CF0 - spans the membrane, forms a proton channel for H+ travel from the thylakoid lumen to the stroma

• CF1 - protrudes into stroma, contains catalytic subunits for ATP synthesis from ADP and Pi

CF0

• - spans the membrane, forms a proton channel for H+ travel from the thylakoid lumen to the stroma

CF1

• protrudes into stroma, contains catalytic subunits for ATP synthesis from ADP and Pi

how many photons per atp

2.7

cyclic phosphorylation

• when no co2 is available or no NADP+, no electrons accepted from ferredoxin

• cytochrome bf complex used instead

• protons are pumped but no oxygen or nadph produced

• 2 photons per atp