What is the Difference Between Photosystem 1 and Photosystem 2?

Photosystem 1 (PS1) and Photosystem 2 (PS2) are multi-protein complexes involved in oxygenic photosynthesis. They contain pigments that help collect light energy and play a crucial role in the light-dependent reactions of photosynthesis. The key differences between PS1 and PS2 are:

1. Location: PS1 is located on the outer surface of the thylakoid membrane, while PS2 is located on the inner surface of the thylakoid membrane.
2. Photocenter: The photocenter of PS1 is called P700, while the photocenter of PS2 is called P680.
3. Light Absorption: PS1 absorbs light of longer wavelengths (> 680 nm), while PS2 absorbs light of shorter wavelengths (< 680 nm).
4. Reaction: PS1 uses light energy to convert NADP+ to NADPH2, while PS2 uses light energy to dissociate water molecules.
5. Protein Complex: PS1 has a comparatively smaller number of proteins (about 15 subunits) in its core complex, while PS2 has a multi-subunit complex in its core complex.
6. Pigment Composition: PS1 comprises chlorophyll A-695, chlorophyll A-670, chlorophyll A-680, chlorophyll A-700, chlorophyll B, and carotenoids, while PS2 comprises chlorophyll A-670, chlorophyll A-660, chlorophyll A-695, chlorophyll A-680, chlorophyll A-700, chlorophyll B, phycobilins, and xanthophylls.
7. Involvement in Photolysis: PS1 is not involved in the photolysis of water, while PS2 is involved in the photolysis of water.
8. Photophosphorylation: PS1 participates in both cyclic and non-cyclic photophosphorylation, while PS2 participates in non-cyclic photophosphorylation.

In summary, Photosystem 1 and Photosystem 2 have distinct roles, locations, and compositions in the light-dependent reactions of photosynthesis.

Comparative Table: Photosystem 1 vs Photosystem 2

The key differences between Photosystem 1 (PS I) and Photosystem 2 (PS II) are their absorption wavelengths and the pigments involved in their reaction centers:

Both photosystems are multi-subunit membrane-protein complexes involved in oxygenic photosynthesis. They play crucial roles in converting light energy into chemical energy during the light reaction of photosynthesis.