light dependent reaction

how are thylakoids adapted for the light dependent reaction?

• large SA - can contain more chlorophyll and e^- carriers

• ATP synthase channels - allow the synthesis of ATP

• selectively permeable - allows a H⁺ gradient to be established

what happens when a chlorophyll molecule absorbs light energy?

• a pair of e^- become excited and are raised to a higher E level

• the e^- leave the chlorophyll molecule and are passed onto an e^- carrier - chlorophyll gets oxidised and the e^- carrier gets reduced 

• the e^- are passed along a series of e^- carriers in the thylakoid membranes

• each e^- carrier is at a slightly lower energy E stage so e^- lose E as they are passed along

what is the e^- transport chain?

series of membrane bound e^- carrier proteins

give the key stages of the light dependent reaction:

PSII:

1. absorption of light energy and photoionisation

2. photolysis of water

3. e^- transfer along the e^- transport chain and chemiosmotic synthesis of ATP 

PSI:

4. e^- transfer along the e^- transport chain and chemiosmotic synthesis of ATP

overall final step: reduction of NADP → NADPH

describe the absorption of light energy and photoionisation:

• light absorbed by accessory pigments and E transferred to chlorophyll a

• photoionisation = primary e^- acceptor captures excited e^- from chlorophyll a

• this initiates the oxidation of chlorophyll 

describe the photolysis of water and give the equation:

• chlorophyll a is now +vely charged, causing photolysis to occur

• photolysis = the splitting of H₂O into H⁺ ions and O₂ molecules

• H₂O → 2H⁺ + 2e^- + ½ O₂

• chlorophyll a accepts an e^- from water to replace the one lost to the primary e^- acceptor

describe e^- transfer along the e^- transport chain:

• e^- passes from the primary e^- acceptor down the e^- transport chain, causing it to lose E

• the E lost from the e^- is used for the chemiosmotic synthesis of ATP

• when the e^- reaches the bottom of the ETC, it replaces the last e^- excited in photosystem I

describe the chemiosmotic synthesis of ATP:

• e^- from 1^o e^- acceptor travel down an e^- transport chain, losing energy which is used to pump H⁺ across the thylakoid membrane into the thylakoid space 

• H⁺ diffuse into the stroma via ATP synthase

• this movement combines ADP + Pi → ATP

describe the reduction of NADP: 

• e^- passes down another ETC

• H⁺ from photolysis and e^- are accepted by NADP - final e^- acceptor

• NADP is reduced to NADPH by NADP reductase - catalysed by dehydrogenase

• NADPH carried into LIR

give the eqn for the reduction of NADP to NADPH:

NADP + 2H⁺ + 2e^- → NADPH

what is a coenzyme? give an example:

• coenzyme = organic, non protein compound which catalyses a reaction through binding with another enzyme

• e.g. NADP