The Calvin cycle refers to the succession of biochemical processes that develop in chloroplasts.
The Greek word kýklos , which can be translated as "circle" , derived from the Latin cyclus . This is the closest etymological antecedent of cycle , a term that has several uses.
The succession of phases that a periodic phenomenon goes through is called a cycle ; to the time span that encompasses various characteristic events: to the stage that, once completed, begins again; and the set of actions or events that are repeated in a certain order.
Calvin , meanwhile, is the surname of an American chemist who won the Nobel Prize in Chemistry : Melvin Calvin , born in 1911 in Minnesota and died in 1997 in California . This scientist, along with other colleagues, made important discoveries regarding how plants assimilate carbon dioxide ( CO2 ).
What is the Calvin cycle
The Calvin cycle refers to the biochemical processes that take place in chloroplasts , the organelles that carry out photosynthesis in plants. These processes specifically make possible the so-called second phase of photosynthesis , which encompasses reactions that are independent of light and that allow the fixation of CO2 .
In this framework, CO2 enters the leaves of plants thanks to the stomata (pores) and then reaches the stroma (internal space) of the chloroplast , where the Calvin cycle takes place. Since these reactions are not caused by light directly, they are classified as independent.
The Calvin cycle allows for the synthesis of sugar . This is because the carbon atoms present in CO2 bind to organic molecules, promoting the formation of three-carbon sugars thanks to the stimulation carried out by adenosine triphosphate ( ATP ) and nicotinamide adenine dinucleotide phosphate ( NADPH ).
Within the framework of the Calvin cycle, carbon fixation and then the formation of glucose occur.
How it develops
The Calvin cycle can be divided into three major phases. The first stage is carbon fixation , with the combination between the CO2 molecule and the RuBP molecule. This generates a six-carbon compound that fragments into a pair of three-carbon molecules ( 3-PGA ).
The next step is reduction , with ATP and NADPH driving the conversion of 3-PGA molecules into G3P molecules (a three-carbon sugar). Finally, while there are G3P molecules that form glucose , others are recycled for the regeneration of the RuBP acceptor.
The discovery of the Calvin cycle
In addition to Melvin Calvin , who bequeathed his name to the naming of the cycle, other scientists made important contributions in this matter. Andrew Benson and James Bassham worked together with Calvin in a laboratory at the University of California at Berkeley .
Thus, in the '40s , these specialists investigated the development of photosynthesis in Chlorella pyrenoidosa , a unicellular algae. Through various experiments, they managed to separate the compounds they obtained and identify them using carbon 14 .
With the new knowledge, Calvin and company were able to determine how green areas of plants assimilate CO2 . In 1961 , for his important work, Calvin received the Nobel Prize in Chemistry .