lec 14 slide 22

in the non-cyclic photosynthetic electron transfer rewaction, Where is light energy first harvested in photosynthesis?

In the antenna complexes of Photosystem II (PSII)

Where is the harvested energy transferred in PSII?

To P680, the special pair chlorophyll in the reaction center

What happens after P680 absorbs energy?

Charge separation occurs → P680 loses an electron to the ETC

How does P680 restore its lost electron and become neutral again

By splitting water, which donates electrons and produces O₂

going back to that ionized electron, What is the first mobile electron carrier after PSII?

Plastoquinone (PQ)

What is the next step after plastoquinone?

Electron is transferred to cytochrome b6-f complex, which pumps 2 protons per electron into the thylakoid space

After cytochrome b6-f, where does the electron go?

To plastocyanin (PC), which resides in the thylakoid space

Where does plastocyanin transfer the electron?

To P700, the special pair chlorophyll in Photosystem I (PSI)

How does PSI excite the electron for transfer to ferredoxin?

Light energy absorbed by antenna complexes is transferred to P700 via resonance energy transfer, causing charge separation

After PSI, where does the electron go?

To ferredoxin in the stroma, then to ferredoxin-NADP⁺ reductase (FNR)

: What does FNR do with the electron?

Reduces NADP⁺ to NADPH

How is ATP produced during photosynthesis?

Proton motive force (PMF) generated by the ETC drives ATP synthase, producing ATP

What are the products of the light reactions?

ATP and NADPH, which are used for carbon fixation → converting CO₂ to glyceraldehyde-3-phosphate (G3P)

Why is cyclic photophosphorylation needed?

To produce extra ATP relative to NADPH for the Calvin cycle

: How does cyclic photophosphorylation work?

Electron from ferredoxin is cycled back to plastoquinone, passing through the ETC again → proton pumping → more ATP