Photophosphorylation is the conversion of adenosine diphosphate to adenosine triphosphate using light energy through photosynthesis. It is the mechanism through which energy-enriched adenosine triphosphate molecules are produced in the presence of light by transferring the phosphate group to the adenosine diphosphate molecule.
Since phosphorylation happens in the visible region of the light, it is referred to as photophosphorylation. There are two forms of photophosphorylation: Cyclic photophosphorylation and non-cyclic photophosphorylation.
Cyclic Photophosphorylation vs Non-Cyclic Photophosphorylation
The main difference between cyclic photophosphorylation and non-cyclic photophosphorylation is that cyclic photophosphorylation develops through anoxygenic photosynthesis, whereas non-cyclic photophosphorylation takes place during oxygenic photosynthesis.
Cyclic photophosphorylation is a phenomenon that develops in the cyclic motion of electrons to generate adenosine triphosphate molecules. Plant cells make adenosine diphosphate to adenosine triphosphate during this process to achieve instant energy for the cells. Cyclic photophosphorylation is a mechanism that happens in the thylakoid membrane and utilizes Chlorophyll P700 and Photosystem I.
Non-cyclic photophosphorylation is a mechanism that leads to the non-cyclic transfer of electrons to manufacture adenosine triphosphate molecules utilizing the power from the photo-generated electrons given by Photosystem II. Because the electrons emitted via P680 of Photosystem II are taken with P700 of Photosystem I and therefore do not return to P680, this mechanism is known as non-cyclic photophosphorylation.
Comparison Table Between Cyclic Photophosphorylation And Non-Cyclic Photophosphorylation
| Parameters of Comparison | Cyclic Photophosphorylation | Non-Cyclic Photophosphorylation |
| Presence | This is most common among photosynthetic bacteria. | It is found mostly in higher plants, algae, and cyanobacteria. |
| Electron flow pattern | Electrons flow in a cyclic or circular manner. | Electrons flow in a zig-zag pattern in a uniform manner. |
| Release of oxygen | During cyclic photophosphorylation, no oxygen is produced. | Non-cyclic photophosphorylation produces molecular oxygen. |
| Involvement of photosystem | Only photosystem-I is involved. | It is made up of photosystems I and II. |
| Creation of energy | In this procedure, just adenosine triphosphate is generated. | This process generates adenosine triphosphate and NADPH. |
What is Cyclic Photophosphorylation?
Cyclic Photophosphorylation is the mechanism by which organisms (such as prokaryotes) simply convert adenosine diphosphate to adenosine triphosphate for quick energy. This form of photophosphorylation is mostly found in the thylakoid membrane. In cyclic electron transport, the electron originates in a pigment compound termed photosystem I.
It then moves from the main acceptor to ferredoxin and subsequently to cytochrome b6f. Cytochrome b6f is comparable to mitochondrial cytochrome b6f. After that, the electron travels through plastocyanin until reverting to chlorophyll.
Throughout the whole electron acceptor chain, a proton-motive force is created, which pumps H+ ions out of the cell and creates a pressure gradient that may be utilized to activate adenosine triphosphate synthase during chemiosmosis. This entire process is referred to as cyclic photophosphorylation. It does not generate O2
Even during cyclic photophosphorylation reaction, electrons are transported back to P700 from the acceptor and therefore do not travel to NADP. Consequently, descending the flow of electrons to the P700, adenosine triphosphate molecules are produced.
Bacterial photosynthesis uses a single photosystem, which is engaged in cyclic photophosphorylation. It is preferred in anaerobic circumstances, as well as high irradiation and CO2 compensation points. Cyclic photophosphorylation is always necessary since it produces adenosine triphosphate at a cheap cost. In cyclic photophosphorylation, only photosystem-I is engaged.
What is Non-Cyclic Photophosphorylation?
Non-cyclic photophosphorylation is a two-step process that involves two distinct chlorophyll photons. Non-cyclic photophosphorylation happens in the thylakoid membrane as a light response. High light intensity promotes non-cyclic photophosphorylation.
Non-cyclic photophosphorylation is prevalent in all vegetation, algae, and cyanobacteria. PS-II absorbs photons from the source of light and transmits them to RC chlorophyll.
The electrons produced by the P700 are absorbed by the main acceptor and subsequently transferred over to the NADP via the non-cyclic photophosphorylation pathway. The electrons interact with both the protons H+ generated when the water particles break to decrease NADP into NADPH.
The energy in this kind does not transmit the entire cycle and does not return to the chlorophyll as it is used in the elimination of NADP+. This is the only way electrons transfer from a molecule of water to NADPH. As a result, it is known as non-cyclic photophosphorylation.
It is also often known as the Z-scheme. An electron from chlorophyll travels out through an electron transfer system and consequently minimizes NADP+ to create a unit of NADPH of this kind. Glycerate 3-phosphate is the fundamental building block from which plants may produce a wide range of compounds. Non-cyclic photosynthetic respiration produces molecular oxygen in the contribution of energy molecules.
Main Differences Between Cyclic Photophosphorylation And Non-Cyclic Photophosphorylation
- The process of making adenosine triphosphate during the cyclic electron transport system of light – dependent reactions photosynthesis is referred to as cyclic photophosphorylation. Whereas Non-cyclic photophosphorylation is the method by which adenosine triphosphate is produced from the noncyclic electron transport in photosynthetic light processes.
- Cyclic photophosphorylation is not connected with water photolysis and hence does not free oxygen whereas non-cyclic photophosphorylation is linked with water photolysis and oxygen liberation,
- Cyclic photophosphorylation occurs when light demand is reduced, anaerobic circumstances exist, or co2 availability is low, whereas non-cyclic photophosphorylation occurs when light intensity increases, aerobic conditions exist, and co2 is present.
- Cyclic photophosphorylation requires ATP synthesis, but non-cyclic photophosphorylation requires ATP synthesis as well as the generation of NADPH.
- Cyclic photophosphorylation involves just photosynthesis I whereas non-cyclic photophosphorylation involves both photosynthesis I and II.
Conclusion
Cyclic Photophosphorylation is a mechanism in which an electron emitted by the stimulated photo center is restored via a succession of electron transport chains. When electrons travel via Ferredoxin to PQ and to the Cytochrome system, ATP is generated.
However, the normal mechanism wherein the electron released by the stimulated photo center does not revert is non-cyclic phosphorylation. It is carried out in conjunction with both photosystems I and II.
As a result, we may now infer that cyclic and noncyclic photophosphorylation is light-dependent photosynthesizing processes that phosphorylate to create adenosine triphosphate. The photosynthetic cells then using the adenosine triphosphate conduct different actions that aid in their existence and advancement.
References
- https://www.sciencedirect.com/science/article/pii/0005272872901430
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC223143/