Photosynthesis

Stage 1- Light Reactions

Friday, June 12, 15

6CO2

Chloroplasts - convert light energy into glucose

Light Reactions

Calvin Cycle

Photosynthesis

Overall reaction:

C6H12O6+ 12H2O + 6H2O6O2 +Photosynthesis occurs in two stages:

thylakoid of chloroplast

stroma of chloroplast

Friday, June 12, 15

Pigments are organized into 2 photosystems

Pigments embedded in thylakoid membrane absorb energy from sunlight and give up electrons to membrane proteins

Light Reactions

Light reactions occur in 3 steps:Overview

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What is a photosystem? Collection of

photosynthetic pigments linked

together

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el

ectro

ns

Overall result is formation of ATP + NADPH - used in Calvin cycle to construct glucose

Movement of electrons and H+ ions leads to production of NADPH and ATP

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Electrons released by pigments are replaced by splitting of H2O (photolysis) producing O2

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Pigments are organized into 2 photosystems

Pigments embedded in thylakoid membrane absorb energy from sunlight and give up electrons to membrane proteins

Light Reactions

Light reactions occur in 3 steps:Overview

�

Friday, June 12, 15

Step �

Light ReactionsOverview

StromaThylakoidhigh [H+] low [H+]

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- Photolysis (splitting of water by light) provides electrons to replace those lost by chlorophyll a and oxygen gas

Light ReactionsThe Specifics

- Light energy of a certain wavelength (680nm) excites chlorophyll a in photosystem II causing release of electrons

Light

P680

Stroma

ThylakoidspaceH20 ½O2

electrons

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- H+ ion gradient used to power synthesis of ATP

- Just as with E.T.C., the movement of electrons through thylakoid membrane results in build up of H+ ions within thylakoid space

Light

P680

Stroma

ThylakoidspaceH20 ½O2

Light ReactionsThe Specifics - Electrons released by

chlorophyll a transferred through series of proteins in thylakoid membrane until they reach photosystem I

electronsHigh [H+]

ATP

ADP+ P

Friday, June 12, 15

Light

P680

Stroma

ThylakoidspaceH20 ½O2

electronsHigh [H+]

Light ReactionsThe Specifics

- Light energy (700nm) excites chlorophyll a in photosystem I causing electrons to move into second series of membrane proteins

P700

- Coenzyme NADP+ is the final electron acceptor. It is reduced to form NADPH

Light

NADPH

NADP+

ATP

ADP+ P

Friday, June 12, 15

Light

P680

Stroma

ThylakoidspaceH20 ½O2

electronsHigh [H+]

Light ReactionsThe Specifics

- ATP and NADPH are used in Calvin Cycle to build organic molecules like glucose

P700

- Coenzyme NADP+ is the final electron acceptor. It is reduced to form NADPH

Light

NADPH

NADP+

ATP

ADP+ P

Calvin Cycle

Friday, June 12, 15