Calvin cycle

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The Calvin cycle.

The Calvin cycle (also known as the Calvin–Benson cycle) is the set of chemical reactions that take place in chloroplasts during photosynthesis.

The cycle is light-independent because it takes place after the energy has been captured from sunlight.

The Calvin cycle is named after Melvin Calvin, who won a Nobel Prize in Chemistry for finding it in 1961.[1] Calvin and his colleagues did the work at the University of California, Berkeley.[2]

Context[change | change source]

Using the radioactive carbon-14 isotope as a tracer, Calvin, Andrew Benson and their team mapped the complete route that carbon travels through a plant during photosynthesis. They traced the carbon-14 from its absorption as atmospheric carbon dioxide to its conversion into carbohydrates and other organic compounds.[3][4] The single-celled algae Chlorella was used to trace the carbon-14.[5]

The Calvin group showed that sunlight acts on the chlorophyll in a plant to fuel the manufacture of organic compounds, not directly on carbon dioxide as previously believed.

Steps[change | change source]

The steps in the cycle are as follows: [6]

1. Grab: A five-carbon carbon catcher catches one molecule of carbon dioxide and forms a six-carbon molecule.

2. Split: the enzyme RuBisCO (with the energy of ATP and NADPH molecules) breaks the six-carbon molecule into two equal parts.

3. Leave: A trio of three carbons leave and become sugar. The other trio moves on to the next step.

4. Switch: Using ATP and NADPH, the three carbon molecule is changed into a five carbon molecule.

5. The cycle starts over again.

The product[change | change source]

The carbohydrate products of the Calvin cycle are three-carbon sugar phosphate molecules, or 'triose phosphates' (G3P). Each step of the cycle has its own enzyme which speeds up the reaction.

References[change | change source]

  1. "The Nobel Prize in Chemistry 1961 Melvin Calvin". Retrieved January 14, 2011.
  2. Bassham J, Benson A, Calvin M (1950). "The path of carbon in photosynthesis". J Biol Chem 185 (2): 781–7. PMID 14774424.
  3. Calvin M. 1956, "The photosynthetic cycle.", Bull. Soc. Chim. Biol. 38 (11): 1233–44, PMID 13383309
  4. Barker S.A. et al 1956, "Intermediates in the photosynthetic cycle.", Biochim. Biophys. Acta 21 (2): 376–7, doi:10.1016/0006-3002(56)90022-1, PMID 13363921
  5. Calvin, Melvin 1961. "The path of carbon in photosynthesis" (PDF). p. 4. Retrieved July 11, 2011.
  6. Sadava, David et al 2009. Life: the science of biology. Macmillan, p199–202. ISBN 1429219629.