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Mechanism of Photosynthesis
according to Calvin cycle......
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Biochimica et Biophysica Acta (BBA) - Bioenergetics

Volume 1322, Issues 2–3, 15 December 1997, Pages 173-182

Control properties of the Calvin photosynthesis cycle at physiological carbon dioxide concentrations

Author links open overlay panelGöstaPettersson

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https://doi.org/10.1016/S0005-2728(97)00080-7Get rights and content

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Abstract

A previously described kinetic model for theCalvin cycle and ancillary pathway of starch production in the chloroplast of C3 plants has been extended so that it becomes applicable under physiological conditions where there is a competition between carbon dioxide and oxygen for ribulose-1,5-bisphosphate carboxylase (rubisco). The modified model is shown to account for the observed dependencies of the rate of carbon dioxide assimilation in leaves on the concentrations of carbon dioxide, oxygen, and rubisco. The predictions of the model are examined with particular regard to the control characteristics of the photosynthetic process ofcarbohydrate formation under physiological conditions.

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Keywords

Calvin cycle

Control analysis

Mathematical modelling

1. Introduction

The Calvin photosynthesis cycle is of outstanding importance for the economy of human communities and for life on Earth in general. Extensive research, therefore, has been directed towards the biological regulation of this metabolic pathway [1–4]. Such research has provided valuable information on a variety of factors that may control and ultimately limit the cycle activity, but a deeper insight into the control patterns that actually apply has been hampered by the extreme kinetic complexity of the reaction system; the Calvin cycle involves 13 enzymes acting on 16 metabolites in an intricate network of reactions, and is dependent on input processes providing the system withATP and NADPH as well as on output steps withdrawing photosynthetic products from the reaction cycle. The kinetic behaviour and regulatory properties of such a complex system cannot be reliably established by intuitive reasoning, but require detailed analysis and characterisation by mathematical modelling.

In previous reports from our laboratory, we have presented a realistic kinetic model of the Calvin cycle and ancillary pathway of starch production in the chloroplast of C3 plants [5]. The model was shown to account satisfactorily for the main rate characteristics of the photosynthetic process ofcarbohydrate production, as determined by experiments with isolated chloroplasts under conditions of carbon dioxide saturation [5, 6].

In this investigation, an extension of the above Calvin cycle model is described which renders the model applicable at physiological concentrations of carbon dioxide and oxygen by taking the oxygenase activity of ribulose-1,5-phosphate carboxylase (rubisco) into account. The predictions of the modified model are examined for comparison with relevant experimental data and to obtain information on the control pattern governing photosynthetic carbohydrate production in chloroplasts under physiological con

Answer 2

Hey TANNU ☺ , here is your answer................!!


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Calvin Cycle is also known as the dark reaction part of the photosynthesis in which reduction of carbon atoms from carbon dioxide to a reduced state of hexose occurs by utilizing ATP and NADPH produced by the light reactions. Another reason why Calvin Cycle is known to be the dark reaction is because unlike light reactions, this reaction is independent of the presence of light. This cycle was first formed by Melvin Calvin. The Calvin Cycle uses sunlight as an energy source to synthesize glucose from carbon dioxide gas and water for photosynthetic organisms. This introduces all the carbon atoms used as a fuel source and as backbones of biomolecules in life. There are a lot of similarities between the Calvin Cycle and the Pentose Phosphate Pathway. Like mirror images of each other, the pentose phosphate pathway generates NADPH by
breaking down the glucose into carbon dioxide. Similarly, the Calvin Cycle reduces the carbon dioxide to generate hexoses using NADPH.


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