Cyclic, Non-Cyclic and Photophosphorylation

Introduction

The process of converting ADP( Adenosine di- phosphate) to ATP(Adenosine triphosphate) using light energy obtained from photosynthesis is known as photophosphorylation. It is the process of transferring the phosphate group into an ADP molecule in the presence of light to generate energy-rich ATP molecules. Cyclic photophosphorylation is a photophosphorylation mechanism that causes electrons to flow in a cyclic pattern to synthesize ATP molecules. Plant cells simply convert ADP to ATP in this process to provide instant energy to the cells. Photosystem I and chlorophyll P700 are used in this process, which takes place in the thylakoid membrane. Instead of going into NADP from the electron acceptor, electrons are transported back to P700 during cyclic photophosphorylation. The synthesis of ATP molecules is caused by the downward passage of electrons from an acceptor to P700. 

Body

In the chloroplast within the grana, the photosynthetic light reaction occurs. The chemical energy of ATP and NADPH is transformed into light energy in this process. Photophosphorylation is a phenomenon that occurs when phosphate is added in the presence of sunshine or during the creation of ATP by cells. 

The energy generated in the light reaction of photosynthesis is used to transform carbon dioxide into carbohydrates in the dark reaction of photosynthesis. The stroma of the chloroplasts undergoes this process.

Photophosphorylation

Photophosphorylation is the conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) using the light energy released during photosynthesis (ATP). The process of transferring the phosphate group to the ADP molecule in the presence of sunlight results in the production of energy-rich ATP molecules. ATP is produced by everybody and is considered the universal energy currency of all living forms. Photolysis or photodissociation of water, as well as a continuous flow of electrons from water to photosystem II in one direction, is a common feature of photosynthesis.

Light energy is employed to create a high-energy electron donor and a lower-energy electron acceptor during photophosphorylation. Electrons are then transported in a chain from the donor to the acceptor in real-time.

Two Different Types of Photophosphorylation 

1. Cyclic photophosphorylation
2. Non-cyclic photophosphorylation

Cyclic Photophosphorylation 

The process of cyclic photophosphorylation involves the recycling of electrons. In this type of photophosphorylation the electrons emitted from the reaction centre return back to the reaction centre. In this process only PSI participates.In this process only ATPs are generated neither oxygen nor NADPH2 are generated.. This occurs in the stroma lamellae. 

Note: Only one photosystem is required for bacterial photosynthesis, it is engaged in cyclic photophosphorylation. It’s perfect for anaerobic environments, high irradiance and CO2 compensation points.

Non-cyclic Photophosphorylation

When the electrons emitted from the reaction center of the photosystem do not return to the same reaction center but move on to different centers it is called non- cyclic photophosphorylation. In this process both the photosystems participate i.e. PSI and PSII. During this process ATPs and NADPH2 are generated along with the liberation of oxygen..A photosystem, which is filled with chlorophyll, is one of the elements of the thylakoid membrane. 

ATP and Reaction 

ATP synthase is an enzyme that produces ATP. In all known forms of life, the structure of this enzyme and its main gene are very similar.

A transmembrane electrochemical potential channel, generally in the form of a proton channel, drives ATP synthase. The electron transport chain’s job is to create this gradient. A series of redox processes are employed in all living organisms to produce a transmembrane electrochemical potential gradient, often known as the proton motive force (pmf).

Redox reactions involve the transfer of electrons from a donor to an acceptor molecule. The Gibbs free energy of the reactants and products acts as the primary driving factor in these reactions. Gibbs free energy is the energy that is supplied to accomplish work (“for free”). Any reaction that lowers a system’s total Gibbs free energy will occur spontaneously (if the structure is isobaric and adiabatic), while kinetically hindered reactions may take longer to complete.

The transfer of electrons from a high-energy (donor) to a lower-energy (acceptor) molecule may be broken down into a series of intermediate redox processes. 

The fact that a reaction is thermodynamically conceivable does not guarantee that it will really take place. A mixture of hydrogen and oxygen can’t burn spontaneously. For most biological reactions to continue at a meaningful pace, it is essential to either contribute activation energy or reduce the system’s inherent activation energy. To reduce the activation energy of biological processes, living systems adopt more complex macromolecular structures.

A thermodynamic process that moves from a higher-energy state to a lower-energy state, such as charge separation or the generation of an osmotic gradient, in such a manner that the total free energy of the system lowers, making it thermodynamically viable while useful work is accomplished.

Conclusion

Non-cyclic photophosphorylation is a photophosphorylation mechanism that causes electrons to flow in a non-cyclic fashion to synthesize ATP molecules utilizing the energy from excited electrons given by photosystem II. So, in non-cyclic photophosphorylation, you produce oxygen by splitting the water molecule, ATP by utilizing H+ ions, and NADPH. Only photosystem I use is cyclic photophosphorylation. The electrons exclusively come from the light-harvesting complex, hence there is no water splitting.