BI220 - Photosynthesis: Light Reactions

photosystem

• large complex of proteins and pigments optimized to harvest light

• functional unit of photosynthesis

main components of photosystem

• LHC

• RCC

• primary electron acceptor

lights harvesting complexes

• contains chlorophylls (a and b) bound to proteins

reaction-center complex

• protein complex w/ special pair of chlorophyll a molecules

primary electron acceptor

• protein found in reaction center that initiates light reactions

PSII

• P680

PSI

• P700

how do photosystem use light energy

• transfer e- to adjacent molecule

  • energy used to synthesize ATP and NADPH

what molecule is oxidized to donate e- to PSII

H2O

what is the final e- acceptor at the end of light reactions

NADP+ → NADPH

where in the chloroplast is the concentration of H+ the highest

thylakoid space

how is the proton gradient established across thylakoid membrane

• H20 split into O2 and H+ by PSII

• cytochrome B6F pump H+ into lumen

how is potential energy used by ATP synthase to generate ATP

• atp synthase runs via chemiosmosis

  • spinning of internal rod and rotor activate sites that produce ATP from ADP and Pi

what is important about Cytochrome B6f

• uses exothermic rxn to pump H+ into thylakoid space

NADP+

• electron carrier/acceptor

NADPH

• electron donor

  • provides energy for biochemical reactions

chemiosmosis

generating ATP via proton gradient

where do light reactions occur

thylakoid membrane

where is NADPH released

stroma

draw model of photosynthesis

draw diagram of photosystem embedded in thylakoid membrane

• label 3 main components