Calvin cycle


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Fig. 86 Calvin cycle . The ‘dark’ reactions of the Calvin cycle.

Calvin cycle

a series of chemical reactions, first described by Melvin CALVIN, which take place in the watery matrix of CHLOROPLASTS, where carbon dioxide is incorporated into more complex molecules and eventually carbohydrate. Energy for the reactions is supplied by ATP with NADPH (see NADP acting as a reducing agent, both having been produced in the light reactions of PHOTOSYNTHESIS. Since light is not required for the Calvin cycle to continue (provided CO2 ,ATP and NADPH are present) the steps are called the ‘dark’ reactions.

Every turn of the cycle fixes one molecule of carbon dioxide by producing two molecules of PGA and then two molecules of PGAL; three turns are necessary to release one molecule of PGAL (C3) for the glucose pathway with the remaining five PGAL molecules remaining within the cycle. Thus six turns produce sufficient quantities of PGAL for the production of one molecule of glucose (C3 + C3 = C6).

References in periodicals archive ?
The Calvin cycle, which has also come to be known as the C3 pathway because the first detectable product is a 3-carbon compound, is not the only means by which green plants fix carbon or incorporate it into sugars.
The process has come to be known as the C3 pathway or the Calvin cycle. In his final years of active research, he studied the use of oil-producing plants as renewable sources of energy.
Then this carbon is fixed just as it is in the normal Calvin cycle metabolism.
Instead of partitioning metabolites in space (between mesophyll and bundle sheath cells), CAM plants use PEP carboxylase to fix the carbon into malate, which is then stored until the next day, when the carbon is released and refixed in normal Calvin cycle metabolism.
Most plants can get by with the simplest form of the Calvin cycle, in which a catalyst called RuBP combines with [CO.sub.2] to create sugars.
The intermediary molecule formed by these plants in the Calvin cycle is a four-carbon compound, so these are known as C4 plants.
The story of the Calvin Cycle: Bringing carbon fixation to life.
An example is The Story of the Calvin Cycle, described here, in which students trace the biochemical steps of the Calvin cycle through a musical play.
In my classroom, the details of the Calvin cycle (formally the Calvin-Benson-Basham cycle) are presented after a general discussion of the big picture of photosynthesis in the global ecology of the planet.
* the relationship between the Calvin cycle and the products of the photochemical reactions