- What is the Calvin Cycle?
- Stages of the Calvin cycle
- Function of the Calvin Cycle
- Importance of the Calvin Cycle
- Calvin cycle products
We explain what the Calvin Cycle is, its stages, its function and its products. Also, its importance for autotrophic organisms.
What is the Calvin Cycle?
It is known as the Calvin Cycle, the Calvin-Benson Cycle or the Cycle of carbon fixation in the photosynthesis, to a set of biochemical processes that take place in the stomata of the chloroplasts of the plants and other organisms autotrophs whose nutrition It is carried out through photosynthesis.
The reactions that make up this cycle belong to the so-called dark phase of the photosynthetic process or phase independent of the light, during which the carbon dioxide (CO2) taken from the atmosphere, incorporating it into the body in the form of glucose (C6H12O6) thanks to the action of enzyme RuBisCo (ribulose-1,5-bisphosphate carboxylase / oxygenase).
The Calvin Cycle owes its name to its discoverer, the American Melvin Calvin, which earned him the Nobel Prize for Chemistry in 1961. His other important collaborators on the study were James Bassham and Andrew Benson, all from the University of California, Berkeley.
Stages of the Calvin cycle
The Calvin cycle is made up of three distinct stages:
- Stage 1. CO2 fixation, the enzyme RuBisCo catalyzes the carboxylation of ribulose diphosphate, that is, the fixation of carbon dioxide to form PGA (3-Phosphoglyceric Acid).
- Step 2. Reduction of PGA to a sugar (CH2O) through the formation of glycealdehyde-3-phosphate (GAP) with NADPH (Nicotidamide adenine dinucleotide phosphate) and the 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 has a fundamental role in plant life: generating glucose, one of the main sugars (out of six atoms carbon) of use biochemical as a source of energy and structural or storage material.
The cycle uses six molecules of CO2 to obtain one of glucose, attaching them to various receptors in a repeated circuit of chemical reactions that consumes Energy (ATP). Six turns of the cycle are necessary to compose a glucose molecule. In addition, every 3 turns of the cycle a molecule of triose phosphate is produced, used in other processes such as the synthesis of starch.
Importance of the Calvin Cycle
The Calvin cycle is the only route metabolic used by autotrophic organisms to incorporate the inorganic material on which they feed, just like atmospheric CO2, 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 energy is stored in plant tissues that is transmitted upwards in the trophic pyramid, serving as food for the herbivorous animals, which in turn serve as food to their predators.
On the other hand, this process of fixing the carbon contained in CO2, a well-known gas of greenhouse effect, contributes to the cooling of the atmosphere and with the reduction of the gases responsible for the global warming and the climate change. That is why today is more important than ever.
Calvin cycle products
The Calvin Cycle produces a fixed carbon atom in each of its turns, so it takes three turns of the cycle (and the entry of three CO2 molecules, one 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.