lec 14 slide 18

What is a photosystem composed of?

• Reaction center → contains the special pair chlorophyll that undergoes charge separation

• Antenna complexes → capture light energy and transfer it to the reaction center

why is antenna complexes important

it is where most of the energy is absorbed and transferred to get charge separation in the special pair

what is transferred in antenna complexes

ENERGY

Which chlorophyll in a photosystem undergoes charge separation?

Only the special pair chlorophyll in the reaction center

Why can’t the special pair chlorophyll absorb enough energy on its own?

Because it can absorb ~1 photon/sec, which is not enough for continuous charge separation.

What is the role of the antenna complexes?

• Absorb most of the light energy

• Transfer energy (not electrons) to the special pair via resonance energy transfer

• Increase efficiency of light gathering

Does charge separation happen in the antenna complexes?

No — only energy transfer occurs.

How is energy transferred from the antenna complexes to the special pair?

By resonance energy transfer from chlorophyll to chlorophyll until it reaches the reaction center.

What happens after the special pair receives energy?

It undergoes charge separation → electron is transferred to a mobile quinone → enters the ETC → pumps protons.

How does the special pair chlorophyll restore its lost electron?

By taking an electron from water.

Why are antenna complexes important for photosynthesis?

They increase light-harvesting efficiency and funnel energy to the special pair to enable effective charge separation.