In both cyclic and non cyclic phosphorylation?
In both cyclic and non-cyclic phosphorylation, light energy is absorbed by chlorophyll in the photosystem and is used to excite electrons. However, there are some differences between the two processes.
1. Cyclic phosphorylation: This type of phosphorylation occurs only in photosystem I. The excited electrons are passed through an electron transport chain, which generates ATP through chemiosmosis. The electrons are then returned to chlorophyll in photosystem I, creating a cyclic electron flow. Only ATP is produced during cyclic phosphorylation, and no reducing agents such as NADPH are generated.
2. Non-cyclic phosphorylation: This type of phosphorylation involves both photosystems I and II. Excited electrons are passed from photosystem II to photosystem I through an electron transport chain. This generates both ATP and NADPH. In addition, photosystem II also splits water molecules to release oxygen gas as a byproduct. The overall process of non-cyclic phosphorylation provides both energy (ATP) and reducing power (NADPH) for the light-independent reactions of photosynthesis.
Overall, cyclic phosphorylation is a simpler process that generates only ATP, while non-cyclic phosphorylation is a more complex process that produces both ATP and reducing agents like NADPH.
In both cyclic and non-cyclic phosphorylation, the process of photosynthesis occurs. Here are the steps involved in each:
1. Cyclic Phosphorylation:
- Light energy is absorbed by chlorophyll molecules in the thylakoid membrane of the chloroplast.
- Electrons from chlorophyll are excited and transferred to a primary electron acceptor molecule in the Photosystem I (PS I).
- The excited electrons pass through a series of electron carriers in the electron transport chain (ETC) located in the thylakoid membrane.
- As the electrons move through the ETC, energy is released and used to actively transport protons (H+) across the membrane from the stroma into the thylakoid lumen.
- The accumulation of protons creates a proton gradient that drives the synthesis of ATP through ATP synthase.
- The electrons, after losing energy, return back to chlorophyll in PS I.
2. Non-Cyclic Phosphorylation:
- Light energy is absorbed by pigment molecules, primarily chlorophyll, in both Photosystem II (PS II) and the antennae complex.
- Excited electrons are donated by water, splitting it into oxygen, protons (H+), and electrons.
- The electrons from water replace the electrons in PS II, which were excited by light energy.
- The excited electrons from PS II are transferred to a primary electron acceptor and then through an electron transport chain.
- This electron flow generates ATP through chemiosmosis, similar to cyclic phosphorylation.
- Electrons are then transferred from the electron transport chain in PS I and are re-energized by absorbing more light energy.
- These high-energy electrons are used to reduce NADP+ to NADPH.
- The electrons leave PS I and join with protons and NADP+ to form NADPH, which serves as an energy carrier.
It is important to note that non-cyclic phosphorylation produces both ATP and NADPH, while cyclic phosphorylation only produces ATP.