Difference between Cyclic and Noncyclic Photophosphorylation – Comparison Table

compare cyclic and noncyclic photophosphorylation

Cyclic Photophosphorylation vs Non-cyclic Photophosphorylation
(Similarities and Differences between Cyclic and Non-cyclic Photophosphorylation)

The process of photosynthesis is completed in two main steps – Light reaction and Dark reaction. The Light reaction is the light-dependent reaction where the assimilatory powers (ATP and reduced coenzymes) are generated in the grana of chloroplasts. During the light reaction, photolysis of water and evolution of oxygen take place.

In the dark reaction (light independent reaction), the assimilatory powers synthesized in the light reaction are utilized to reduce the CO2 to carbohydrates.

During the light reaction, energy in the sunlight is captured by the reaction centers of photosystems (PS I and/or PS II) and they expel electrons with high energy. These electrons then pass through a series of complexes called Electron Transport System (ETS) to synthesize the assimilatory powers. During the pathway of electrons through the ETS, phosphorylation reaction occurs at specific points which results in the synthesis of energy-rich APT molecules.

Since this phosphorylation is occurring in presence of light, it is called photophosphorylation. Depending upon the path of electrons in the electron-transport-system of the primary photochemical reaction, there are two types of photophosphorylation processes. They are (1) Cyclic photophosphorylation and (2) Noncyclic photophosphorylation.

The present post discusses the similarities and differences between cyclic and noncyclic photophosphorylation with a comparison table.

Similarities between cyclic and noncyclic phosphorylation

Ø  Both cyclic and noncyclic photophosphorylations are light reactions.

Ø  Both are dependent on light.

Ø  Both are electron transport systems.

Ø  Both pathways produce assimilatory powers.

Ø  In both phosphorylation and formation of ATP occurs.

cyclic vs noncyclic light reaction

Difference between Cyclic and Noncyclic Photophosphorylation

Sl. No.Cyclic Photophosphorylation*Noncyclic photophosphorylation
1As the name suggests, in cyclic photophosphorylation the electrons move in a circular pattern.Electron movement is non-cyclic in noncyclic photophosphorylation.
2Involves only Photosystem I (PS I)Involves both Photosystem I and II (PS I and PS II)
3The electron circle is closedThe electron circle is not closed
4Electron is first expelled from the reaction center of PS I – P700Electron is first expelled from the reaction center of PS II (P680)
5Electron is returned back to the P700 after passing through the electron transport system (ETS)Electron is not returned to the reaction center (P680), rather it is accepted by NADP+
6P700 is the electron donor and the final electron acceptorP680 is the first electron donor and NADP+ is the final electron acceptor
7Photolysis of water does not occurPhotolysis of water occur
8Oxygen is not evolvedOxygen is evolved
9Synthesize only ATP, no reduced coenzymes are synthesizedSynthesize both ATP and reduced coenzymes
10Cyclic photophosphorylation usually occurs at low light intensityNon-cyclic photophosphorylation is favoured by high light intensity
11During anaerobic condition, the cyclic photophosphorylation predominatesDuring aerobic condition, the non-cyclic photophosphorylation is predominates
12Occurs when the concentration of CO2 is less in the atmosphereOccurs when the concentration of CO2 is sufficient in the atmosphere
13Predominantly occurs in isolated chloroplasts and bacterial photosynthesisPredominantly occurs in green plants
14Insensitive to DCMU # (cannot be inhibited by DCMU)Sensitive to DCMU (can be inhibited by DCMU)

*Photophosphorylation: The addition of phosphate group in the presence of light during the light reaction of photosynthesis is called photophosphorylation. Photophosphorylation results in the formation of ATP during light reaction.

# DCMU: It is an inhibitor of photosynthesis commonly known by the trade name Diuron. Chemically DCMU is 3-3,4-dichlorophenyl-1,1-dimethylurea. It is commonly used as an algicide and herbicide.

Cyclic Photophosphorylation (diagram)

Noncyclic Photophosphorylation (diagram)

z scheme of ATP synthesis

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