We explain what the Calvin Cycle is, its stages, its function and its products. Furthermore, its importance for autotrophic organisms.
What is the Calvin Cycle?
It is known as the Calvin Cycle, the Calvin-Benson Cycle or the Carbon Fixation Cycle in Photosynthesis, a set of biochemical processes that take place in the stomata of plant chloroplasts and other autotrophic organisms whose nutrition is carried out through photosynthesis.
The reactions that make up this cycle belong to the so-called dark phase of the photosynthetic process or light-independent phase, during which carbon dioxide (CO) is fixed2) taken from the atmosphere incorporating it into the body in the form of glucose (C6h12EITHER6) thanks to the action of the enzyme RuBisCo (ribulose-1,5-bisphosphate carboxylase/oxygenase).
The Calvin Cycle It owes its name to its discoverer, the American Melvin Calvin which earned him the Nobel Prize in Chemistry in 1961. Other important collaborators of his on the study were James Bassham and Andrew Benson, all of the University of California, Berkeley.
See also: Glycolysis
Stages of the Calvin cycle
The Calvin cycle is made up of three distinct stages:
- Stage 1. CO fixation2the RuBisCo enzyme catalyzes the carboxylation of ribulose diphosphate, that is, the fixation of carbon dioxide to form PGA (3-Phosphoglyceric Acid).
- Stage 2 Reduction of PGA to a sugar (CH2O) through the formation of glycealdehyde-3-phosphate (GAP) with NADPH (Nicotidamide adenine dinucleotide phosphate) and ATP (Adenosine Triphosphate) produced in light-dependent reactions.
- Stage 3 Regeneration of ribulose diphosphate, which requires ATP as well.
Function of the Calvin Cycle
The Calvin Cycle plays a fundamental role in the life of plants: generate glucose one of the main sugars (six carbon atoms) of biochemical use as energy source and structural or storage material.
The cycle uses six CO molecules2 to obtain one from glucose, adhering them to various receptors in a repeated circuit of chemical reactions that consume energy (ATP). Six turns of the cycle are necessary to make one molecule of glucose. In addition, every 3 turns of the cycle a molecule of triose phosphate is produced, used in other processes such as starch synthesis.
Importance of the Calvin Cycle
The Calvin cycle is the only metabolic pathway that autotrophic organisms use to incorporate the inorganic matter on which they feed just like CO2 atmospheric, which breathing organisms expel from their bodies. This occurs in both photosynthetic and chemosynthetic organisms.
At the same time, this process is of tremendous ecological importance, since in this cycle in plant tissues energy is stored and transmitted upward in the trophic pyramid serving as food for herbivorous animals, which in turn serve as food for their predators.
On the other hand, this process of fixing the carbon contained in the CO2a known greenhouse gas, contributes to the cooling of the atmosphere and with the reduction of gases responsible for global warming and climate change. Therefore, today it is more important than ever.
Calvin cycle products
The Calvin Cycle produces a fixed carbon atom in each of its turns, so three turns of the cycle are needed (and the entry of three CO molecules2one at a time) to form a molecule of Glyceraldehyde-3-phosphate (3GP). Thus, part of the material produced can be recycled to reactivate RuBisCo and another part can be used for the production of glucose.
Continue with: Carbon Cycle
References
- “Calvin Cycle” on Wikipedia.
- “The Calvin Cycle” at Khan Academy.
- “Photosynthesis III. Dark Phase: Calvin Cycle (Via C3)” (video) in network efficiency.
- “The Calvin Cycle” (video) on Ricochet Science.
- “The Calvin Cycle” on Lumen Learning.
- “Calvin Cycle” in Biology Dictionary.
- “C-3 Cycle” in The Encyclopaedia Britannica.
