What is the Calvin Cycle?

We explain what is the Calvin Cycle, its stages, its function and its products. In addition, its importance for autotrophic organisms.

1. What is the Calvin Cycle?

It is known as the Calvin Cycle, the Calvin-Benson Cycle or the Cycle of carbon fixation in photosynthesis , a set of biochemical processes that take place in the stomata of plant chloroplasts and other autotrophic organisms 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 independent phase of light, during which the carbon dioxide (CO ₂ ) taken from the atmosphere is fixed , incorporating it into the body in the form of glucose (C ₆ H ₁₂ O ₆ ) thanks to the action of the 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 in Chemistry in 1961. Other important collaborators in the study were James Bassham and Andrew Benson, all from the University of California, Berkeley .

2. Stages of the Calvin cycle

The Calvin cycle consists of three distinct stages:

• Stage 1 : Fixation of CO ₂ , the 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 (CH ₂ O) through the formation of glycealdehyde-3-phosphate (GAP) with NADPH (Nicotidamide adenine dinucleotide phosphate) and ATP (Adenosine Triphosphate) produced in the reactions dependent on the light.
• Stage 3 : Regeneration of ribulose diphosphate, which requires ATP as well.

3. Calvin Cycle Function

The Calvin Cycle has a fundamental role in the life of plants: generating glucose , one of the main sugars (of six carbon atoms) for biochemical use as a source of energy and structural or storage material .

The cycle uses six molecules of CO ₂ to obtain glucose, adhering them to various receptors on a repeated chemical reactions circuit consuming energy (ATP). Six rounds of the cycle are necessary to compose a glucose molecule. In addition, every 3 laps of the cycle produces a molecule of triosa phosphate, used in other processes such as starch synthesis.

4. Importance of the Calvin Cycle

The Calvin cycle is the only metabolic route that autotrophic organisms use to incorporate the inorganic matter from which they feed , such as atmospheric CO ₂ , that the breathing organisms expel from their organisms. This occurs in both photosynthetic and chemosynthetic organisms.

At the same time, this process is of tremendous ecological importance, since in this cycle in the plant tissues energy is stored that is transmitted upwards in the trophic pyramid , serving as food for herbivorous animals, which in turn serve of food to their predators .

On the other hand, this process of fixing the carbon contained in CO ₂ , a known greenhouse gas , contributes to the cooling of the atmosphere and the reduction of gases responsible for global warming and climate change. Therefore, today is more important than ever.