In the world of genetic code, if one quality is valued it is abstraction. To understand the processes that happen in a millimetric way in each of our cells as if it were a perfect work chain, we need imagination and, above all, knowledge.
That is why it is common for the average reader to feel scared when dealing with certain topics regarding genetics: “DNA”, “RNA”, “polymerase”, “metagenomics” and many other terms seem to escape general knowledge. Nothing is further from reality.
Like everything in this life, the science of the processes encoded by the genetics of organisms can be explained simply and easily. In this space you will find a summary explanation about what a codon is and how without this functional unit, life as we know it would not be possible.
A codon is a sequence of three nucleotides that is located in messenger RNA It is clear that to understand the functioning of this very special subunit, we must first understand the terms contained in its most general definition.
About the RNA and its organization
The acronym for RNA corresponds to the term “ribonucleic acid”. It is a polymer chain made up of a series of monomers, in this case, nucleotides. Each nucleotide is made up of three different components :
RNA differs from DNA, among many other things, in that the latter has the nitrogenous base thymine (T) instead of uracil (U). In general, nucleotides are named according to the nitrogenous base they carry.
Once we have dissected what a nucleotide is, the first conflictive term in the definition of the codon, it is time for us to clarify what exactly messenger RNA is. To do this, we have to first go to the types of RNA These are the following:
As we have seen, Each type of RNA plays an essential role in protein synthesis : one translates and transports the information from the DNA, another takes the assembly “blocks” to the ribosomes where proteins are synthesized and another is part of the synthesizing “machinery” itself. It seems incredible that such a seemingly simple molecule can perform such complex jobs, right?
There are other types of RNA, such as RNA interference, MICRO RNAs, long non-coding RNAs…etc. We will explain them on another occasion, since these complex ribonucleic acids are far from the term to be discussed.
Now that you have understood all the main types of RNA, it is time to find out why the term codon is so important.
The importance of the genetic code
The genetic code is a term that responds to the set of instructions that tell the cell how to synthesize a specific protein That is, the letters that we have seen previously, both DNA and RNA. In DNA, the code for each gene combines the four letters (A,G,C, and T) in different ways to form three-letter “words,” which specify each of the amino acids that make up a protein.
These “words” encoded in DNA are transcribed through a process called transcription, by which a segment (gene) of DNA gives rise to the messenger RNA explained above. This RNA is mobile, therefore, it can leave the cell nucleus where the genetic information is located and transport the instructions for the synthesis of that protein to the ribosomes (located in the cytoplasm).
Each of the “three-letter words” of DNA translated and contained in the mRNA is, as you may have already guessed, the codon that concerns us today. We can say, therefore, that each of these nucleotide triplets is the most basic functional unit of the genetic code
There are 64 different codons common to all living beings, of which 61 code for amino acids. For most living beings there are 20 different amino acids , and it should be noted that each of them (not in all cases but in almost all) are encoded by 2, 3, 4 or 6 different codons. Therefore, and applying basic mathematics, an amino acid made from 6 codons would be encoded by 18 translated nucleotides (remember that each codon is three ribonucleotides).
The role of the codon in translation
We have established that transcription is the process by which information is transcribed from DNA into an mRNA that will carry the protein synthesis instructions to the ribosomes, right? Well, the codon plays a role, even more important if possible, in the translation process.
Translation is defined as the process of translate (forgive the redundancy) a messenger RNA molecule into a sequence of amino acids that will give rise to a specific protein As we have already mentioned previously, the transfer RNA (tRNA) is responsible for transferring the amino acids to the construction area (the ribosome), but not only that, since it is also responsible for arranging them along the RNA molecule. delivery courier.
For it, tRNA has a sequence of three nucleotides that match those of the codon : the anticodon. This allows this ribonucleic acid to recognize the order of the amino acids of the protein, according to the instructions provided by the codons of the mRNA.
Codons and mutations
A point mutation occurs when a single base pair (nucleotide) of the genetic code is altered. In the case of codons, It is usual for the third of the letters to differ for the synthesis of the same amino acid
For example, leucine responds to the CUU, CUC, CUA codons. Thus, mutations in the third letter are considered silent, since the same amino acid is synthesized and the protein can be assembled without problems. On the other hand, mutations in the first and second letters can be harmful, since they usually result in an amino acid different from the one sought, thus breaking the elaborate assembly chain.
Beyond genetics
As we have seen, this association of three nucleotides known as a codon is one of the basic functional units of the individual’s genetic code. Although the genetic information itself does not change throughout the life of the living being, the expression of genes can Epigenetics is responsible for exploring these mechanisms.
In the DNA of living beings, various genes can be silenced, which results in the inhibition of some transcription and translation processes of certain proteins at the cellular level. If the genetic information is not transcribed into the mRNA, each of the codons will not occur, and therefore, they will not be able to be translated into amino acids and the protein in question will not be assembled.
Conclusions
In these lines we have tried to convey that the codon is a form of organization of genetic information essential for protein synthesis at the cellular level in living beings These proteins make up cells, therefore also tissues, which allows the formation of the living being in question.
Therefore, we are not exaggerating when we say that without this triplet of nucleotides, life as we know it today would not be possible.
