Calvin Cycle

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Carbon Fixation

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Reduction Reaction

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calvin-cycleCalvin Cycle

The Calvin cycle was discovered by Melvin Calvin, James Bassham, and Andrew Benson. It is also referred to as the Calvin-Benson-Bassham cycle. They utilized a radioactive isotope carbon 14 to make this discovery.

The Calvin cycle is a light independent reaction that turns carbon dioxide into glucose. It occurs in the stoma of plants during photosynthesis through a series of chemical reactions, and with the help of ATP and NADH. The Calvin cycle consists of three stages: carbon fixation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.

Stage 1 – Carbon fixation

Carbon dioxide is combined with the 5 carbon molecule ribulose-1,5-bisphosphate (RuBP). This combination results in a 6 carbon molecule. The enzyme rubisco reacts with this molecule to form 2 3-carbon molecules, called 3-phosphoglyceric acid (3-PGA).

Stage 2 - Reduction Reactions

rubiscoTwo molecules of ATP and two molecules of NADH react with the two molecules of 3-PGA during this stage. The reaction changes the 3-PGA to glyceraldehyde-3-phosphate (G3P). The resulting molecules are 3 carbon molecules. This stage is called a reduction reaction because the NADH gives electrons to the 3-PGA to reduce it.

Stage 3 - Ribulose 1,5-Bisphosphate (RuBP) Regeneration

During this final stage, two different things happen to the G3P molecules. There will be some molecules that will be turned into glucose. These will be used to create energy in the cells. There will also be some molecules that will be regenerated to form the RuBP that is needed in the first stage of the process. The main goal of this cycle is to create glucose, which will be used to create energy in the cells. In order for the one molecule of glucose to be made, the cycle has to run six times to produce the two G3P required to make glucose.

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