LOCATION OF PHOTOSYNTHETIC PIGMENTS IN PHOTOSYNTHESIS:
Photosynthetic pigments are chlorophyll a , chlorophyll b ,and carotenoids these are associated with protein forming pigment protein complexes. The pigment molecules associated with the PS-I are located in the non appressed part as well as stroma thylakoids where as those associated with PS-II are located more towards the appressed part of the grana thylakoids.
• PHOTOSYNTHESIS
This is two step process:
1.Light reaction or photochemical reaction—-The assimilatory power is generated in thylakoids.
2. Dark reaction or thermochemical reaction—-Fixation of CO₂ into carbohydrated this takes place in stroma of chloroplast.
TWO PIGMENT SYSTEMS PS—I & PS—II :
Light reaction of photosynthesis involves participation of pigment systems PS—I & PS–II
Each photosystem have a pigment protein complex composed of chlorophyll a , chlorophyll b , carotenoids & other components required in electron transport. Each pigment protein complex consist of a core complex ( 40-50 chlorophyll molecules) & an antenna complex.The role of core and antenna complex is to absorb maximum solar radiations.
PS—I : Single chlorophyll a700 or P₇₀₀ molecule in the centre surrounded by 200-400 chlorophyll a ,b , 50 carotenoids & two iron comtaining proteins similar to ferrodoxin called Fe-S proteins which harvest maximum solar radiation. The Fe-S protein is the primary electron acceptor of PS-I. PS-I has more chlorophyll a molecules than the other pigments, It is located both on the non apperesed part of grana thylakoids as well as Fret channels ( stroma thylakoids) mostly towards the outer surface of membrane.PS-I is involved in both cyclic & non cyclic electron transports and in non cyclic electron transport it drives electron from PS-II to NADP⁺.
PS—II : It has Single chlorophyll a₆₈₀ or
P₆₈₀ molecule in the centre surrounded by other accesory molecules which include 200chlorophyll a , b , 50 carotenoids
& its primary electron acceptor pheophytin.It also
has Quinone (Q)
which quenches molecule from P₆₈₀ ,
Manganese bound protein & an water oxidizing enzyme . It has equal amount
of chlorophyll a & b & located in appresed parts of grana thylakoids towards inner side of the membrane.It is
associated with non cyclic electron transport chain, splitting of water,
evolution of oxygen and reduction of NADP⁺ TO NADPH.
| PS-Is | PSII |
| 1. Centre molecule absorb light of 700 nm that’s why P₇₀₀. | 1.Centre molecule absorb light of 680nm that’s whyP₆₈₀ . |
| 2. located both on the non apperesed part of grana thylakoids as well as Fret channels ( stroma thylakoids) mostly towards the outer surface of membrane. | 2.located in appresed parts of grana thylakoids towards inner side of the membrane |
| 3. Its primary electron acceptor Fe-S protein . | 3. Its primary electron acceptor pheophytin |
| 4. PS-I is involved in both cyclic & non cyclic electron transports | 4.It is associated with non cyclic electron transport chain only. |
| 5. It is light green in colour. | 5. It is dark green in colour. |
| 6. It reduces NADP⁺ to NADPH. | 6. It donates electron to PS-I when NADP⁺ is reduced. |