DNA Translation: What It Is And What Are Its Phases
DNA translation is the second process of protein synthesis It occurs in all living beings and takes place in the cytoplasm, where ribosomes are found, which play a fundamental role in the process.
Translation does not happen suddenly. It is necessary that a first step has been taken first, transcription, in which the genetic material in the form of DNA is transcribed into the aforementioned RNA molecule. Let’s see how it happens and what is necessary for it to happen.
It is common knowledge that DNA, specifically Its sections, the genes, contain the genetic information about how we are However, for genes to be able to encode information and cause proteins to be synthesized, an entire process of reading and coding DNA, RNA of different types, is necessary, in addition to the involvement of ribosomes.
There are two steps necessary to transform the information hidden in a gene into a well-made protein:
The first is DNA transcription. A DNA sequence, that is, a gene, is made up of nucleotides which are adenine, thymine, guanine and cytosine (A,T,G and C, respectively).
During transcription, the piece of DNA is transcribed into an RNA molecule (ribonucleic acid), which differs from DNA in that, instead of containing the nucleotide thymine (T), it has uracil (U). A is complementary to T, and C to U. This RNA is processed and trimmed, becoming a messenger RNA (mRNA).
After transcription comes translation, which is the step in which the RNA is read to form a polypeptide chain, which is basically a protein but with a very linear structure For this to happen, it is necessary to join amino acids, which will depend on the nucleotides in the RNA.
As we were already saying, during translation the information contained in the mRNA is read, using it as if it were the instruction manual to form a chain of amino acids, that is, a polypeptide. It is in this phase that what could be considered the structure immediately prior to the protein will be obtained which is basically a chain of amino acids but with a three-dimensional structure.
Each sequence of three nucleotides, called codons, of the mRNA (A, G, C and U) corresponds to a specific amino acid, or to a start or stop signal. The triplets that encode the end of polypeptide synthesis are UGA, UAG and UAA, while the AUG codon encodes the start signal and also the amino acid methionine.
Together, the codon-amino acid relationships are what make up the genetic code It is what allows cells to decode, through mRNA, a chain of nucleotides into a chain of amino acids. To understand it better, below we have a chain of mRNA, with nucleotides. Next to it, we have the amino acids that correspond to each triplet of nucleotides, in addition to the start and end signals.
The role of ribosomes and tRNA
Before going into detail about how DNA translation occurs, We are going to talk about the two elements that allow the mRNA to be read and a chain to be synthesized: ribosomes and transfer RNA.
transfer RNA (tRNA)
Transfer RNA (tRNA) is a type of RNA that serves as a molecular bridge to connect the codons of the mRNA to the amino acids for which they code. Without this type of RNA, it would not be possible to relate an amino acid to the triplet of nucleotides present in the mRNA
In each tRNA there is an end that has a three-nucleotide sequence, called an anticodon, that is complementary to the triplet of nucleotides in mRNA. At the other end they carry the amino acid.
Ribosomes are organelles made up of two subunits with an appearance similar to that of two hamburger buns: the large subunit and the small subunit. In the ribosome, there are also three hollow places where the tRNA joins with the mRNA: sites A, P and E. It is in the ribosomes where polypeptides are built.
The large and small subunits gather around the mRNA and, through enzymatic action, the ribosome catalyzes a chemical reaction that joins the amino acids of the tRNA to form a polypeptide chain.
DNA translation: the process
Every second, our cells produce hundreds of proteins. This is why translation is such an important process for life, since without it we would be left without the ability to transform the information contained in genes into something useful. DNA translation occurs in three stages: initiation, elongation and termination.
Initiation
The initiation of DNA translation occurs at the ribosome This organelle is assembled around an mRNA molecule, where a tRNA will come.
This last type of RNA must carry the amino acid methionine, encoded by the AUG codon, which is the signal to start the synthesis of the polypeptide chain.
This ribosome-tRNA-mRNA-methionine assembly is known as the initiation complex, and is necessary for translation to occur.
Elongation
Elongation, as its name suggests, is the stage in which amino acids are added to the polypeptide chain, making it increasingly longer As more triplets of nucleotides are translated from the mRNA, the more amino acids the polypeptide will have.
Each time a new codon is exposed, a corresponding tRNA binds. The existing amino acid chain joins the tRNA amino acid through a chemical reaction. The mRNA moves one codon on the ribosome, exposing a new codon to be read.
Within elongation we can distinguish three stages:
In the first, an anticodon, that is, a tRNA triplet that contains bases complementary to those of an mRNA triplet “pairs” with an exposed mRNA codon in the A site.
A peptide bond is formed, through the catalytic action of aminoacyl-tRNA synthetase, between the new amino acid introduced and the one immediately before it. The new amino acid is located in the A site of the ribosome, while the previous one is in the P. After the bond is formed, the polypeptide is transferred from the P to the A site.
The ribosome advances a codon on the mRNA The tRNA in the A site carrying the polypeptide moves to the P site. It then moves to the E site and exits the ribosome.
This process is repeated many times, as many times as new amino acids are placed, if a signal has not previously appeared indicating that the continuation of the polypeptide chain must be stopped.
Termination
Termination is the moment in which the polypeptide chain is released, stopping growing. It begins when a stop codon (UAG, UAA, or UGA) appears on the mRNA. This, When it is introduced into the ribosome, it triggers a series of events that result, as a final result, in the separation of the strand of its tRNA allowing it to float towards the cytosol.
It may be the case that, despite termination, the polypeptide still needs to take the correct three-dimensional shape, in order for it to become a well-formed protein.
Although, in essence, proteins are polypeptide chains, their difference from the newly manufactured polypeptide chains in the ribosomal complex is that they have a three-dimensional shape, while the new polypeptide chain of lashing is, basically, a very linear chain of amino acids.
