Ribosomes: function, structure and relationship with nucleic acids

The Ribosomes Are small corpuscles that are responsible for the synthesis of proteins. They are parts of the cell found in large quantities and therefore abundant in those membranes of the endoplasmic reticulum, where ergatoplasma forms. Its shape is oblong (longer than wide) and its size is 250 x 150 ångström (equivalent to about 20 or 30 nanometers in diameter).

Looking at the microscope, the ribosomes are shaped like dark grains, both in the endoplasmic reticulum, in the nuclear membrane and in the cytosol. This is indisputable proof of their high number, which can rise (per cell) to several million. The cytoplasmic corpuscles form a component that is constant in the matrix of the cell, which is close to this endoplasmic reticulum and more specifically in the excretory cells in which granular masses are formed.


Therefore, it can be said that ribosomes are never in a state of isolation, but always tend to concentrate, to form very dense accumulations of granules that not in vain cover the rough endoplasmic reticulum (the smooth endoplasmic reticulum, on the other hand, Is free of these corpuscles). However, ribosomes may also wander in the cytoplasm or may be associated with the membranes of the endoplasmic reticulum. This means that ribosomes make up a complex in the cell structure.

This complex is mainly characterized by being ribonucleoproteic, ie, ribosomes are composed of a ribonucleotide that is Ribonucleic Acid (RNA) and proteins that, in equal parts, are accompanied by minimal amounts of lipids (organic compounds that have Fatty acids, for example cholesterol).

Ribosomes, in themselves, are cataloged as organelles and also as oblong particles. In the structure of the cell the ribosomes have a role that distinguishes them, and a series of parts that compose it, which explains its operation. Similarly, these corpuscles are notable for their close relationship with RNA and the complex biochemical process of protein synthesis in living beings.


Ribosomes are linked directly to protein synthesis, and this has to be emphasized, since this is a very important role.

These granular corpuscles have the function of making the genetic instructions of the RNA link the specific sequences of the amino acids with which the proteins are made. The mission of ribosomes is to create proteins starting from amino acids.


When making a longitudinal cut of these corpuscles, which is visible in the microscope, you can distinguish several parts that are easy to identify but have a complex relationship to each other. In their most superficial aspects, the ribosomes consist of three relevant elements: one, the double inner membrane that covers them; Two, the crests or folds that are situated in its interior; And three, the intermembranous spaces arising from these folds.

In contrast to the external structure, the inner part of the ribosomes is much more intricate and has much more specific functions that may vary according to the organisms studied, although some common traits are maintained, both in animal cells and in plant cells. To make this clearer, ribosomes have subunits that are not going to be the same in oaks, bacteria, dogs and much less in humans. Every living being is unique in its kind.

See for example the bacterium whose scientific name is Thermus thermophilus . He Thermus thermophilus Has only two subunits, one major and one minor. In the greater the amount of proteins surpasses thirty, whereas the smaller one has twenty. However, in both subunits they have an RNA that forms the nucleus of the ribosomes, both at the structural and functional levels. Their proteins also build bridges between subunits and between nucleic acids.

More specifically, in the Thermus thermophilus It is observed that the major subunit has more than thirty RNA helices grouped into six secondary domains that are listed with Roman numerals (from domain I to domain VI) and that they interlock with each other very firmly. The major subunit, of course, has proteins located mostly in its peripheral region, just outside, but the RNA remains on the surface, ready to enter into the longed for genetic contact.

The lower subunit of the Thermus thermophilus Is quite different from the previous one, described in the previous paragraph. In this subunit there are fewer secondary domains (four in total) and all are named differently than domains of the major subunit that during the protein synthesis act on their own, in full biochemical independence. However, here the position of the RNA (on the surface) and of the proteins (on the periphery) is the same as in the other subunit.

The subunits of ribosomes in humans, of course, differ greatly from those in the Thermus thermophilus . While this bacterium has two subunits, the man has four and also has enough proteins. At Homo sapiens Only one of its subunits performs the protein synthesis outside the nucleolus (granular structure that is in the nucleus) and goes inside to join the ribosome; The other three do this process from that part of the cell.

Structures of ribosomes like the ones just described demonstrate the complexity of cells because each living being has its particularities. This is so because each animal, plant or human organism has a unique genome in its DNA that by extension is applied to the RNA. Therefore, it is not surprising that these corpuscles in the form of grain, despite their similarities, do not stop hiding many nuances at the cellular level.

In addition, and in consonance with the above, it is quite obvious that the structure of the ribosomes is so different between the species. If the RNA is not equal in Thermus thermophilus And in the human being, it is basically because their metabolic requirements are radically different, because bacteria and men do not breathe or feed in the same way. Hence also their protein synthesis is different.

Ratio of ribosomes to nucleic acids

If the biological structure of the ribosomes is different between a living being and another, then its link with nucleic acids also, but this does not mean that there are no points in common. In this vein, protein synthesis is a living example of how these parts of the cell unfold through a direct link with nucleic acids, specifically with RNA, without which any biochemical process would cease to make sense.

In protein synthesis, there are three facets of RNA, each with a very specific function; The first is the messenger RNA (mRNA), the second is the ribosomal RNA (rRNA) and the third is the transfer RNA (tRNA). While the mRNA is responsible for communicating the genetic code, the rRNA deals with protein synthesis in the ribosomes; The tRNA, meanwhile, has the duty to move the molecules of the amino acids.

For the purposes of this article, the whole process of protein synthesis will not be deepened. However, it will be necessary to describe the RNA with its various types, for a reason more than transcendental: living beings, regardless of their classification in taxonomy, experience, and above all, live the cellular changes caused by ribosomes.

It is necessary to remember the comparative of the previous section and to apply it in this context. Note that the Thermus thermophilus Was a bacterium whose two subunits are very different from those that are present in humans. And it is also necessary to see that in that tiny organism has a synthesis of proteins that begins just when its ribosomes come in contact with three tiny molecules of tRNA.

With the Homo sapiens This is not at all different. In humans, the ribosomes are coupled to the mRNA and read the codon with which the initiation phase is given. In the elongation phase it is also seen how the ribosome binds to a tRNA molecule. Already in the termination phase it happens that the subunits of the ribosome get separated from the mRNA in what completes the manufacture of a protein that can be composed with hundreds of amino acids.

In both cases, as in many others there may be, it is more than proven that ribosomes are more than tiny corpuscles irrigated on the surface of the cell, but also exert an extremely vital function without which proteins are not Could produce. Ribosomes are the biochemical translators of RNA and therefore, the amino acids that end up becoming the proteins that the organism needs, regardless of their size.

In addition, it should be noted that ribosomes do not have a minor or sporadic participation in protein synthesis. These parts of the cell are always present throughout the process of coding amino acids, which is why their role is not transient at all, but is constantly in operation, since the living being is in constant exchange of nutrients, energy And genes that flow throughout their anatomical structure.

In short, the importance of ribosomes lies in two fundamental factors. First, there are inherent functions of the cell, which are limited to protein synthesis with all its implications, and secondly is its direct linkage to the different types of RNA (ie: mRNA, rRNA and tRNA) thanks to Which initiates the deciphering of the codes that, on a molecular scale, intervene in the biochemical cycles of life.

Brief glossary of terms

In order to facilitate the reader's comprehension of the terms of biology, here is provided a set of fifteen essential words that are directly related to the theme of the ribosomes. For more information, consult the bibliography.

1- Amino Acid: Those organic chemicals that together make up the proteins.

2- Ångström: Unit length applied at microscopic levels and is therefore used to measure, for example, microorganisms.

3- Biochemical: Which belongs to or is related to the biological and chemical processes of nature.

4- Cytoplasm: Part of the cell that is between the nucleus and the plasma membrane.

5- Codon: Group of three messenger RNA molecules (triplet).

6- Corpuscle: In molecular biology, any body or cell of microscopic size.

7- Granule: In cell biology, particle or body of tiny size that has a grain shape.

8- Longitudinal: Related to the length, that is along any object.

9- Membrane: Soft tissue in sheet form.

10- Molecule: Unit of any chemical substance that preserves its properties.

11- Nucleolus: In the parts of the cell, it is the organelle that is inside the nucleus.

12- Orgánulo: Part of the cell that performs a specific function (eg the ribosome).

13- Protein: Substance of animal and vegetable cells which is composed of amino acids.

14- Endoplasmic reticulum: Network of membranes through which the manufacture and transport of those materials that pass inside the cells with nucleus are realized. It is also called endoplasmic reticulum .

15- Protein Synthesis: Biochemical process in which proteins are made from the separation of DNA in its two strands and the amino acids that bind to the ribosomes.


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  2. Marcey, David (2014). Introduction to ribosome structure [Online article; Angel Herráez, trans.]. Madrid Spain. University of Alcalá. Consulted the 1 of February of 2017, in: biomodel.uah.es.
  3. Nucleus and ribosomes [Online article] (2016). California, United States. Khan Academy. Accessed February 1, 2017, at: khanacademy.org.
  4. Pérez Márquez, Julio (No year). The cell. Ribosomes [Online article]. Madrid Spain. University of Alcalá. Consulted the 1 of February of the 2017, in: uah.es.
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  8. Yusupov, M. M.; Yusupova, G. Z. Et al (2001). "Crystal structure of the ribosome at 5.5 Å resolution". Science , (292), pp. 883-896.

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