DNA translation: what is it and what are its phases?
Overview of how the process of DNA translation occurs, in which proteins are created.
DNA translation is the second process of protein synthesis.. It occurs in all living organisms and takes place in the cytoplasm, where ribosomes, which play a key role in the process, are located.
Translation does not occur suddenly. A first step, transcription, must have taken place beforehand, 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 occur.
What is DNA translation?
It is common knowledge that DNA, specifically its stretches, the genes, contains its stretches, the genes, contain the genetic information on how we are. However, for genes to encode information and synthesize proteins, a whole process of reading and encoding DNA and RNA of different types is necessary, in addition to the involvement of ribosomes.
Two steps are necessary to transform the information hidden in a gene into a well elaborated protein:
The first is DNA transcription. A DNA sequence, i.e., a gene, is made up of nucleotideswhich are adenine, thymine, guanine and cytosine (A, T, G and C, respectively).
During transcription, the piece of DNA is transcribed into an RNA (ribonucleic acid) molecule. (ribonucleic acid), which differs from DNA in that instead of containing the nucleotide thymine (T) it contains uracil (U). A is complementary to T, and C to U. This RNA is processed and trimmed, becoming a messenger RNA (mRNA).
Following transcription comes translation, which is the step in which 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 assemble amino acids, which will depend on the nucleotides in the RNA.
The genetic code
As we were saying, during translation the information contained in the mRNA is read and used as if it were the instruction manual to form a chain of amino acids, i.e. a polypeptide. It is at this stage that what could be considered as the structure immediately preceding the protein will be obtained, which is basically a chain of amino acids.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 termination signal. The triplets encoding 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, by means of mRNA, a chain of nucleotides to a chain of amino acids. To understand it better, below we have an mRNA chain, with nucleotides. Next to it, we have the amino acids corresponding to each nucleotide triplet, as well as the start and termination signals.
- AUG - methionine/start
- GAG - Glutamate
- CUU - Leucine
- AGC - Serine
- UAG - STOP
The Role of Ribosomes and tRNA
Before going into detail with how DNA translation occurs, let's talk about the two elements that allow the mRNA to be read and a strand to be synthesized: the ribosomes and the tRNA.chain is synthesized: the ribosomes and the 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 link an amino acid to the triplet of nucleotides present in the mRNA..
In each tRNA there is one end that has a sequence of three nucleotides, called the anticodon, which is complementary to the mRNA nucleotide triplet. At the other end they carry the amino acid.
Ribosomes are organelles made up of two subunits similar in appearance to two hamburger buns: the large subunit and the small subunit.The large subunit and the small subunit. In the ribosome, in addition, there are three hollow sites where the tRNA binds to the mRNA: the A, P and E sites. It is on the ribosomes that polypeptides are constructed.
The large and small subunits assemble around the mRNA and, by enzymatic action, the ribosome catalyzes a chemical reaction that binds the amino acids of the tRNA together 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 the genes into something useful. DNA translation occurs in three stages: initiation, elongation and termination.
Initiation of DNA translation takes place in the ribosome.. This organelle assembles around an mRNA molecule, where a tRNA will come from.
This last type of RNA must carry the amino acid methionine, encoded by the codon AUG, which is the signal for initiating the synthesis of the polypeptide chain.
This ribosome-mRNA-tRNA-mRNA-methionine assembly is known as the initiation complex, and is necessary for translation to take place.
Elongation, as the name suggests, is the stage in the stage in which amino acids are added to the polypeptide chain, making it longer and longer.. As more nucleotide triplets of the mRNA are translated, the more amino acids the polypeptide will have.
Each time a new codon is exposed, a corresponding tRNA binds. The existing amino acid chain binds to the amino acid in the tRNA by a chemical reaction. The mRNA is displaced one codon on the ribosome, which exposes a new codon to be read.
Within elongation we can distinguish three stages:
In the first, an anticodon, ie, a triplet of the tRNA containing bases complementary to those of an mRNA tripletis "paired" with an exposed codon of the mRNA at the A site.
A peptide bond is formed, through the catalytic action of aminoacyl-tRNA synthetase, between the newly introduced amino acid and the one immediately upstream of it. The new amino acid is in the A site of the ribosome, whereas the previous one is in the P site. After the bond is formed, the polypeptide is transferred from the P to the A site.
The ribosome advances a codon in 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 attached if no signal has appeared beforehand to stop the continuation of the polypeptide chain.
Termination is the moment when the polypeptide chain is released, ceasing to grow. It begins when a termination codon (UAG, UAA or UGA) appears in the mRNA. This, when introduced into the ribosome, triggers a series of events that ultimately results in the cleavage of the strand from its tRNA, allowing it to float to the mRNA.allowing it to float into the cytosol.
It may be the case that, despite termination, the polypeptide still needs to take the correct three-dimensional shape in order 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, whereas the new polypeptide chain from trinca is basically a very linear chain of amino acids.
- Pamela C Champe, Richard A Harvey and Denise R Ferrier (2005). Lippincott's Illustrated Reviews: Biochemistry (3rd ed.). Lippincott Williams & Wilkins. ISBN 0-7817-2265-9
- David L. Nelson and Michael M. Cox (2005). Lehninger Principles of Biochemistry (4th ed.). W. H. Freeman. ISBN 0-7167-4339-6
- Hirokawa et al. (2006). The Ribosome Recycling Step: Consensus or Controversy? Trends in Biochemical Sciences, 31(3), 143-149.
(Updated at Mar 28 / 2023)