Photophosphorylation in Photosynthesis

Study Notes

Definition: Photophosphorylation is the process of generating ATP from light energy in photosynthetic organisms.

Types:

Cyclic photophosphorylation: Occurs in the thylakoid membrane of chloroplasts, generates ATP but not NADPH.
Non-cyclic photophosphorylation: Occurs in the thylakoid membrane of chloroplasts, generates both ATP and NADPH.

Mechanism:

Light absorption: Light is absorbed by pigments such as chlorophyll and other accessory pigments in the thylakoid membrane.
Electron transfer: The energy from light is used to transfer electrons through a series of electron carriers in the thylakoid membrane.
Proton pumping: The energy from electron transfer is used to pump protons across the thylakoid membrane, creating a proton gradient.
ATP synthesis: The proton gradient is used to drive the synthesis of ATP from ADP and Pi through the process of chemiosmosis.
NADPH generation: In non-cyclic photophosphorylation, the electrons transferred ultimately reduce NADP+ to form NADPH.

Importance:

Energy source: Photophosphorylation is the primary source of energy for photosynthetic organisms.
** ATP and NADPH:** The ATP and NADPH generated through photophosphorylation are used to power the Calvin cycle and other metabolic processes.

Key players:

Photosystem I (PSI): Involved in non-cyclic photophosphorylation, generates ATP and NADPH.
Photosystem II (PSII): Involved in non-cyclic photophosphorylation, generates ATP and NADPH.
Cytochrome b6f complex: Involved in cyclic photophosphorylation, generates ATP.
ATP synthase: Generates ATP from ADP and Pi using the proton gradient.

Photophosphorylation is the process of generating ATP from light energy in photosynthetic organisms.

Cyclic photophosphorylation occurs in the thylakoid membrane of chloroplasts and generates ATP but not NADPH.
Non-cyclic photophosphorylation occurs in the thylakoid membrane of chloroplasts and generates both ATP and NADPH.

Light is absorbed by pigments such as chlorophyll and other accessory pigments in the thylakoid membrane.
The energy from light is used to transfer electrons through a series of electron carriers in the thylakoid membrane.
The energy from electron transfer is used to pump protons across the thylakoid membrane, creating a proton gradient.
The proton gradient is used to drive the synthesis of ATP from ADP and Pi through the process of chemiosmosis.
In non-cyclic photophosphorylation, the electrons transferred ultimately reduce NADP+ to form NADPH.

Photophosphorylation is the primary source of energy for photosynthetic organisms.
The ATP and NADPH generated through photophosphorylation are used to power the Calvin cycle and other metabolic processes.

Photosystem I (PSI) is involved in non-cyclic photophosphorylation and generates ATP and NADPH.
Photosystem II (PSII) is involved in non-cyclic photophosphorylation and generates ATP and NADPH.
Cytochrome b6f complex is involved in cyclic photophosphorylation and generates ATP.
ATP synthase generates ATP from ADP and Pi using the proton gradient.