The Calvin cycle began to unravel, from experiments with suspension of green algae of the genus Chl

by Franck Gladis da Cunha Shadow and Silence - tales of Kali (part 5). The "independent" expression of the light not adequately characterizes the second stage of photosynthesis, since in reality there is no photosynthesis no light! But this terminology is used to distinguish events that directly utilize light energy than the use of directly. A separate phase of DEPENDS light of two products of light phase: NADPH and ATP. Light promotes the reactions of the light phase, using H 2 O 2 and releasing. The molecules of ATP and NADPH, which are produced during the light phase to follow the stroma and will be used in the Calvin cycle, but these molecules are not dead, they are transformed in the pipeline into NADP + and ADP and Pi returned to thylakoids, in the pipeline restarting the process, as shown in the conceptual map below.
The second stage of photosynthesis is characterized by the involvement of an enzyme system, hence the name enzymatic step, whose carbon reduction, unfolds in three distinct phases, namely: a) - Fixing or carboxylation b) - Reduction c) - Regeneration the acceptor of atmospheric CO2
a) - Incorporation of the C "Route in the pipeline C3 'or Calvin-Benson cycle (Calvin) b) - Incorporation of the C" Route C4 "or" Hatch-Slack "(C4 cycle) c) - Incorporation of the C" CAM Route "- (Crassulacean Acid Metabolism)
The Calvin cycle began to unravel, from experiments with suspension of green algae of the genus Chlorella, where we demonstrated the presence of 3-phosphoglycerate (GAP or G3P), this compound is considered the first stable product of photosynthesis. For this reason, species that use this cycle are called C3 plants. This compound had short lives 3 carbons, followed quickly to other biochemical pathways which will be used in the production of organic compounds such as amino acids, lipids, or glucose. These other organic compounds synthesized outside the chloroplast are exported from the cell and distributed throughout the plant body through the SAP ELABORATE using the phloem. When the needs of the plant organism are already in the pipeline met, the surplus in the pipeline G3P is used for starch, which is stored in the chloroplast itself, as outlines in the figure below.
This is the Calvin pathway used by most plants and this cycle was named or by cycle C3, having been discovered by Calvin, Benson and Bassham in the pipeline in the 50s. This molecule of 3 carbons not formed directly from three molecules of CO2, but, from the reaction of CO2 with a sugar molecule with five carbon atoms, ribulose 1,5 bisphosphate (RuBP). This reaction is catabolized by the enzyme Ribulose 1, 5-bisphosphate carboxylase / oxygenase in the pipeline called Rubisco, which is present in green leaves. Rubisco Benson, the first enzyme involved in the conversion of carbohydrate to CO2, plays a critical in the pipeline role in the biochemistry of chloroplast, one of the most abundant soluble proteins in this organoid. In plants, Rubisco consists of 2 peptide subunits being greater (L) of 56 kDa and a minor (S) of 14 kDa. In many eukaryotic organisms, the L subunit is encoded by the chloroplast genome itself, while S subunit in the pipeline is encoded by the nucleus, where it is then transported to the chloroplast stroma, yielding an active holoenzyme genome.
a) Carboxylation: The RuBP receives CO2 producing phosphoglycerate (phosphoglycerate - 3PG). In this process, three molecules of RuBP receive three molecules of CO2, forming an unstable molecule 6 carbons, soon 6 form the 3-carbon molecules of phosphoglycerate (3PG).
b) Reduction: the phosphoglycerate (3PG) is reduced to triose phosphate in the presence of ATP and NADPH. The reduction occurs in two stages: first, each of the six molecules of 3-phosphoglycerate to 1,3 BPG is phosphorylated (1,3 bi-phosphoglycerate). PHOSPHORYLATION
After phosphorylation, the 1.3 billion-phosphoglycerate is reduced by NADPH forming 6 molecules of GAP (glyceraldehyde 3-phosphate), which is the FINAL PRODUCT CYCLE C3. Only 1 of these 6 molecules to follow the routes of synthesis, the other 5 will follow different routes to RuBP regeneration. REDUCTION c) regeneration: the RuBP is regenerated from five GAP molecules that follow different routes to form three molecules of ribulose 5-phosphate (Ru5P) which, in the presence of ATP, are phosphorylated, regenerating three molecules ribulose 1,5-bisphosphate (RuBP), closing the cycle. In summary: For each molecule of CO2 incorporated, are required 3 molecules of ATP and 2 molecules of NADPH, from the photochemical phase of photosynthesis, causing the production of GAP (glyceraldehyde 3 - phosphate). The videos below summarizes in the pipeline these three steps of the Calvin cycle, the ideal is to watch the three better understanding of the process. References: 1 - UFLA. Fo