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 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]


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 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.
  3. CALVIN, M (1956), "The photosynthetic cycle.", Bull. Soc. Chim. Biol. 38 (11): 1233–44, 1956 Dec 7, PMID 13383309
  4. Barker, S A; Bassham, J A; Calvin, M; Quarck, U C (1956), "Intermediates in the photosynthetic cycle.", Biochim. Biophys. Acta 21 (2): 376–7, 1956 Aug, doi:10.1016/0006-3002(56)90022-1, PMID 13363921
  5. Melvin Calvin (December 11, 1961). "The path of carbon in photosynthesis" (PDF). p. 4. Retrieved July 11, 2011.
  6. Sadava, David; H. Craig Heller, David M. Hillis, May Berenbaum (2009). Life: The Science of Biology. Macmillan Publishers. pp. 199–202. ISBN 1429219629.