Difference Between Cyclic and Noncyclic Photophosphorylation

Introduction image

Difference between cyclic and noncyclic photophosphorylation is mainly due to the following factors:
Type of photosynthesis: Cyclic photophosphorylation occurs during anoxygenic photosynthesis while noncyclic photophosphorylation occurs in oxygenic photosynthesis.
ATP synthesis: ATP synthesis during the cyclic electron flow of anoxygenic photosynthesis is known as cyclic photophosphorylation. ATP production during the noncyclic electron flow of oxygenic photosynthesis is known as noncyclic photophosphorylation.

Movement of electrons: The electrons in cyclic and non-cyclic photophosphorylation move in a cyclic and straight path, respectively.
Photophosphorylation or photosynthetic phosphorylation is a process in which ATP is produced by the addition of phosphate group into ADP during the light reactions of photosynthesis.

Content: Cyclic and Noncyclic Photophosphorylation

  1. Comparison Chart
  2. Definition
  3. Process
  4. Key Differences
  5. Similarities
  6. Conclusion

Comparison Chart

PropertiesCyclic photophosphorylationNoncyclic photophosphorylation
MeaningCyclic photophosphorylation refers to the process which produces ATP during the cyclic electron transport chain of light dependent photosynthesisNoncyclic photophosphorylation refers to the process which produces ATP from noncyclic electron transport chain in light reactions of photosynthesis
OccurrencePredominantly occurs in photosynthetic bacteriaPrimarily occurs in higher plants, algae and cyanobacteria
Photosynthesis typeIt follows anoxygenic photosynthesisIt follows oxygenic photosynthesis
Flow pattern of electronThe electrons flow in a cyclic or circular patternThe electrons flow linearly in a zig-zag pattern
Photosystem involvedIt involves photosystem-I onlyIt involves photosystem-I and photosystem-II
First electron donorThe first electron donor is PS IWater is the first electron donor
Reaction centreReaction centre PS-I first excites the electronReaction centre PS-II first excites the electron
Final electron acceptorThe final electron acceptor is PS IThe final electron acceptor is NADP+
Photolysis of waterWater do not split during this processWater splits or photolyses
Oxygen productionOxygen is not generated during cyclic photophosphorylationMolecular oxygen is generated in noncyclic photophosphorylation
Energy producedOnly ATP is produced in this processATP and NADPH are produced in this process
Oxygen involvementOccurs during anaerobic conditionsOccurs during aerobic conditions
Carbon dioxide involvementOccurs when the CO2 concentration is less in the atmosphereOccurs at normal CO2 concentration
Effect of DiuronThe process is not inhibited by diuronThe process is sensitive to the diuron

Definition

Cyclic photophosphorylation can define as the light reaction of the photosynthetic process, where the ATP produced couples with the electrons. It only involves PS-I (P700), where the electrons move to and from the photosystem by following a cyclic path.

Noncyclic photophosphorylation can define as the light reaction of photosynthetic process refers to the synthesis of ATP during the light reaction of photosynthesis where an electron donor is required, and oxygen is produced as a byproduct. It involves both the photosystems (PS-I (P700) and PS-II (P680)), where the electrons flow linearly in a zig-zag motion.

Process

Cyclic photophosphorylation

It is the phenomena that involve photosystem-I that absorbs a photon of wavelength (725-1035nm). Green sulfur and nonsulfur bacteria, purple bacteria, acidobacteria etc. carry out cyclic photophosphorylation. As it occurs in bacteria, so the chlorophyll present in them will refer as “Bacteriochlorophyll” where out of four only two participates in the photon absorption, and the other two remains inactive.

cyclic photophosphorylation

Thus, the reaction centre excites the electron to the next state via photon absorption through special pair bacteriochlorophyll. As the high energy electrons leave the reaction centre, it makes the bacteriochlorophyll positively charged. Then the excited electrons pass through many cofactors and protein complexes in the ETS and finally return backs to the final electron acceptor, i.e. photosystem-I. As photosystem II is not used during cyclic photophosphorylation, no oxygen is produced.

Noncyclic Photophosphorylation

It is the phenomena that involve both PS-I and PS-II. Generally, noncyclic photophosphorylation predominantly occurs in all green plants, algae, and cyanobacteria. In this process, photons from the light source are trapped by the PS-II (P680) that transfers the energy to the RC chlorophyll. The electrons which are at a ground state in the RC chlorophyll get excited to a higher energy level. Then the primary electron acceptor receives the e. These photon excited electrons travel through the cytochrome b6f complex to PS-I (P700) via ETS.

During this transfer of electrons, some amount of energy is harnessed by a cell to transport proton molecules (H+) across the thylakoid membrane into the thylakoid lumen. The protons are transported by the plastoquinone. This movement of proton ions across the membrane creates a potential difference between the thylakoid lumen and the chloroplast stroma. The potential difference generates a proton-motive force that is used by a cell to drive free energy, i.e. ATP via an enzyme complex “ATP synthase”. The ATP is then used to transport the H+ from the lumen to the stroma.

Noncyclic photophosphorylation

Then the electron reaches PS-I through plastocyanin to fulfil the electron deficiency of the RC chlorophyll. The electrons pass through the cofactor ferredoxin to the enzyme complex NADP+ reductase. The Electrons and H+ ions go to the NADP+ complex to form NADPH. Then the NADPH (reducing agent) along with ATP is transported to the Calvin cycle to fix carbon dioxide into triose sugars.

Both react with glycerate 3-phosphate to form a triose sugar glyceraldehyde 3-phosphate. G 3-P is the basic building-block from which plants can make a variety of substances. This process liberates molecular oxygen along with ATP and NADPH.

Key Differences Between Cyclic and Noncyclic Photophosphorylation

  1. Cyclic and noncyclic photophosphorylation is the light-dependent photosynthetic pathways that generate ATP by following cyclic and noncyclic electron transport chain, respectively.
  2. Cyclic photophosphorylation follows anoxygenic photosynthesis that predominantly occurs in photosynthetic bacteria like green sulfur and nonsulfur bacteria, purple bacteria etc. Oppositely noncyclic photophosphorylation follows oxygenic photosynthesis that commonly takes place in autotrophic green plants, algae and cyanobacteria.
  3. In cyclic phosphorylation, electrons flow in a cyclic or circular pattern, as it expels out of the PS-I and returns back into it. The electrons flow linearly in a zig-zag pattern in noncyclic phosphorylation, by going out of the PS-II, entering into the PS-I, and finally to the NADP+.
  4. In cyclic phosphorylation, water do not lyse to give protons and oxygen. Oppositely, in noncyclic phosphorylation water molecule photolyses to liberate oxygen into the atmosphere.
  5. Diuron function as an inhibitory agent that is commonly used as herbicide and algaecide that generally inhibits the noncyclic phosphorylation.

Similarities

  • Both cyclic and noncyclic photophosphorylation is the light-dependent photosynthetic reaction.
  • Cyclic and noncyclic photophosphorylation processes are the part of ETS that carry out phosphorylation (addition of phosphate group) or ATP formation.

Conclusion

Therefore, we can conclude that the cyclic and noncyclic photophosphorylation are the light-dependent photosynthetic pathways that carry out phosphorylation to produce ATP. This ATP is then used by the cells of micro and macroorganisms to perform various activities for their growth and survival.

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