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Is RuBisCo the most important protein on the planet?
Is RuBisCO the most important protein on the planet?
From the smallest algae to the largest whale, the sun is the source of all life on this planet and it is photosynthesis that transfers this energy into a more useful form for organisms. The enzyme which initiates this process in the light independent reaction, RuBisCO, is the most abundant globular protein in the world. This reasoning indicates the value of RuBisCO as the amount can be proportional to importance; however, it can also be attributed to the inefficiency of the enzyme so more is needed to perform one function. As the organic carbon in the biosphere ultimately stems from RuBisCO’s fixation of carbon dioxide, it is definitely an essential protein for life. The idea that the proteins which make RuBisCO are more vital can therefore be another line of reasoning. This essay will outline the significance of RuBisCO as well as the relative importance of the proteins involved in its synthesis.
Firstly, RuBisCO’s role in creating organic compounds from carbon dioxide is crucial in three types of carbon fixation. In the most common method, the Calvin cycle, this enzyme catalyses first step of the conversion of ribulose bisphosphate and carbon dioxide into glycerate-3-phosphate which eventually results in the formation of glucose, fats and other proteins. As all living creatures obtain their source of energy from these molecules, there is a direct dependence between life and the action of RuBisCO in photosynthesis. In some conditions, another mechanism is employed, C4 fixation, which isolates RuBisCO from atmospheric oxygen and saturates it with carbon dioxide. Similarly, CAM photosynthesis is also a carbon fixation pathway centering around RuBisCO. Carbon dioxide is concentrated around the enzyme so the stomata remain closed during the day in arid conditions to reduce water loss. However, while these are the methods of carbon fixation in plants, there are other ways which do not require RuBisCO. For example, in some bacteria, the reverse Krebs cycle is used to produce carbon compounds from carbon dioxide and water with several steps catalysed by minerals. The reductive acetyl-CoA pathway and the 3-Hydroxypropionate pathway are also employed by archaea as a way of fixing carbon. Although this indicates that organic compounds can be synthesized without RuBisCO, organisms still rely on plants for their net primary production of energy– and plants use RuBisCO for all three types of carbon fixation.
While organic compounds are the basis of life, oxygen is vital to sustain this life. Although RuBisCO contributes a small amount of oxygen to the atmosphere due to its lack of specificity for carbon dioxide as a substrate, most of the atmospheric oxygen is released by the light dependent reactions of photosynthesis. RuBisCO still has an effect on this production, despite being part of the light independent process, because without this enzyme, NADPH will build up in the stroma if it is not converted back to NADP in the Calvin cycle. This directly affects non-cyclic photophosphorylation as the hydrogen created by the photolysis of water cannot reduce any more NADP and the flow of electrons through the transfer chain will also be obstructed. The result of less oxygen molecules being released will not only have an impact on respiration of organisms but also influence the ozone layer. As the ozone layer acts as a shield against harmful UV rays, the indirect link between RuBisCO and its depletion could have varied effects from the increased risk of skin cancer to damaging crops and ocean life.
Recognising the many processes which are connected to the functioning of RuBisCO, either directly through the Calvin cycle or indirectly through the interdependence of different processes emphasizes the actual importance of this enzyme on the planet. However, RuBisCO would not be functioning effectively without the other proteins which assist in its synthesis and folding. From DNA helicase which unzips the double helix to expose the right gene and RNA polymerase which produces the mRNA strand coding for this gene to those involved in the later stages of protein folding such as molecular chaperones to help RuBisCO assemble into a biologically active complex, there are many proteins working together to create RuBisCO in its working form. Developing on this argument, ribosomal proteins involved in translation play a very significant role in the making of RuBisCO. On a larger scale, all the other proteins behind RuBisCO were also synthesized on ribosomes whose assembly and functions are assisted by the ribosomal proteins.
In conclusion, the importance of RuBisCO is supported by its role in two fundamental processes that define life on this planet – the production of organic compounds necessary for life to exist and formation of oxygen needed to maintain life. However, RuBisCO cannot be labeled the most important protein on the planet mainly because of the range of supporting proteins which help synthesise it.
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