Cyclic electron flow around photosystem
Photosystem
Photosystems are functional and structural units of protein complexes involved in photosynthesis that together carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons.
Adenosine triphosphate
Adenosine triphosphate is a complex organic chemical that provides energy to drive many processes in living cells, e.g. muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all forms of life, ATP is often referred to as the "molecular unit of currency" of i…
What is the purpose of the cyclic electron flow?
What is the purpose of cyclic electron flow? In higher plants, the generation of proton gradient across the thylakoid membrane (ΔpH) through cyclic electron flow (CEF) has mainly two functions: (1) to generate ATP and balance the ATP/NADPH energy budget, and (2) to protect photosystems I and II against photoinhibition.
Does cyclic electron flow use light?
In cyclic electron flow, light energy harvested at photosystem I is used for ATP synthesis rather than NADPH synthesis (Figure 10.23). Instead of being transferred to NADP+, high-energy electrons from photosystem I are transferred to the cytochrome bfcomplex.
What is linear and cyclic electron flow?
Linear electron flow is the electrons that pass through the two photosystems from water to NADP+. Cyclic electron flow are the electrons excited from P700 in PSI are passed from Fd to the cytochrome complex and back to P700. What does non cyclic electron flow produce?
What does the cyclic electron flow generate?
Cyclic Electron Flow It results in the production of ATP but not O2 or NADPH. Only photosystem I is present in this reaction. These reactions are meant to produce ATP from ADP and inorganic phosphate in a process called cyclic photophosphorylation by pumping protons across the thylakoid membrane.
Why is cyclic electron flow important for photosynthesis?
The role of cyclic electron transport around PS I is proposed to be essential for balancing the ATP/NADPH production ratio and/or for protecting both photosystems from the damage via stromal over-reduction1.
What is the cyclic pathway in photosynthesis?
Section Summary. The cyclic pathway of photosynthesis uses just photosystem I to generate ATP. This process occurs when sugar production is not immediately necessary and therefore no new NADPH is generated. Electrons are recycled from photosystem I to be continually re-energized until they can be accepted by NADP+.
What are the benefits of cyclic electron flow in photosynthesis quizlet?
What are the benefits of cyclic electron flow in photosynthesis? When a molecule absorbs a photon, it is said to be excited, or at a higher energy state. The excited molecule can then return to its ground state when the absorbed energy is dissipated through mechanisms.
What is the purpose of cyclic electron flow quizlet?
The process of cyclic electron flow allows the cell to generate extra ATP without generating more NADPH, thereby providing enough ATP to carry out the Calvin cycle in the stroma of the chloroplasts.
What does cyclic electron flow mean in biology?
Cyclic Electron Flow in a sense (well, metaphorically) is a 'short circuiting' of the normal z scheme of the light reaction of photosynthesis where energy that otherwise would have gone into making NADPH instead is diverted towards making more ATP.
What are the benefits of cyclic photophosphorylation?
Advantages of Cyclic PhotophosphorylationIt allows for different pigments to absorb huge bands of light.Non-cyclic Photophosphorylation is easier for the plant since it uses only one photosystem.Non-cyclic Photophosphorylation produces ATP and NADPH; cyclic produces the only ATP.
What is the difference between cyclic and noncyclic electron flow?
The non-cyclic photophosphorylation involves both the photosystems and ATP and NADPH are produced, whereas cyclic photophosphorylation involves only PSI and only ATP is produced.
How is noncyclic electron flow the same and different from cyclic flow?
During cyclic photophosphorylation, high energy electrons travel through electron acceptors in cyclic movements and release energy to produce ATP. During noncyclic photophosphorylation, high energy electrons flow through electron acceptors in Z-shaped noncyclic movements.
How is ATP produced by the cyclic pathway?
Cyclic photophosphorylation Light-dependent electron transport occurs in the thylakoid membranes, where electrons follow a cyclic pathway, returning to the photosystem I reaction center. The energy of this electron transport results in a H+ gradient formation, the energy source for ATP synthesis.
What is cyclic reaction?
Cyclic Photophosphorylation. The photophosphorylation process which results in the movement of the electrons in a cyclic manner for synthesizing ATP molecules is called cyclic photophosphorylation. In this process, plant cells just accomplish the ADP to ATP for immediate energy for the cells.
What is the noncyclic pathway of ATP formation?
Noncyclic photophosphorylation involves both Photosystem I and Photosystem II and produces ATP and NADPH. During noncyclic photophosphorylation, the generation of ATP is coupled to a one-way flow of electrons from H2O to NADP+.
Why is there cyclic and non-cyclic photophosphorylation?
So in non-cyclic photophosphorylation, you make oxygen, from splitting the water molecule, you make ATP using the H+ ions and you make NADPH. In cyclic photophosphorylation, you only use photosystem I. There is no splitting of water - the electrons only come from the light harvesting complex.
Abstract
Photosynthesis provides at least two routes through which light energy can be used to generate a proton gradient across the thylakoid membrane of chloroplasts, which is subsequently used to synthesize ATP. In the first route, electrons released from water in photosystem II (PSII) are eventually transferred to NADP + by way of photosystem I (PSI) 1.
Main
In addition to ATP synthesis, generation of ΔpH is required for plants to cope with the changing quantities of light available under natural conditions. Whenever absorption of light energy exceeds its use, increased acidification of the thylakoid lumen induces thermal dissipation of absorbed energy from PSII antennae 6.
Methods
Arabidopsis thaliana wild type (ecotype Columbia gl1) and mutants were cultured in soil for 4–5 weeks under the following conditions: 50 µmol photons m -2 s -1, 16/8 h light/dark cycle and 23 °C. Seedlings analysed in Figs 1e, f and 3 were cultured at a lower light intensity of 20 µmol photons m -2 s -1.
Acknowledgements
We thank M. Miyata and E. Habe for their technical assistance, and T. Mae, A. Makino and G. Peltier for antibodies. A. Portis is acknowledged for his critical reading of the manuscript. T.S. was supported by grants from JSPS.
Author information
Present address: CEA Cadarache, Department of Plant Ecophysiology and Microbiology, 13108, Saint-Paul-lez-Durance Cedex, France