DNA translation is the second process of protein synthesis. It occurs in all living things and takes place in the cytoplasm, where ribosomes are located, which play a key role in the process.
Translation does not happen suddenly. A first step, transcription, must have been carried out previously, 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 it takes to make it happen.
What is DNA translation?
It is well known that DNA, in particular his stretches, his genes, contain genetic information about how we are. However, in order for genes to encode information and make synthesized proteins, a whole process of reading and encoding DNA, RNA of different types, as well as the involvement of ribosomes is required.
Two steps are needed to transform the information hidden in a gene into a well-designed protein:
The first is DNA transcription. A DNA sequence, i.e. 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 thymine nucleotide (T), it contains uracil (U). A is complementary to T and C to U. This RNA is processed and truncated, becoming a messenger RNA (mRNA).
After the transcription comes the translation, which is the step in which RNA is read to form a polypeptide chain, which is basically a protein but very linear in structure. For this to happen, amino acids must be added together, which will depend on the nucleotides in the RNA.
The genetic code
As we have already said, during the translation we read the information contained in the mRNA, used as if it were the manual of instructions to form an amino acid chain, that is to say say 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 but with a three dimensional structure.
Each three nucleotide sequence, called codons, of mRNA (A, G, C and U) corresponds to a specific amino acid, or to a start or end 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.
Taken together, codon-amino acid relationships make up the genetic code. This is what allows cells to decode, via mRNA, a chain of nucleotides into a chain of amino acids. To better understand this, below is an mRNA string, with nucleotides. Next to that, we have the amino acids that correspond to each nucleotide triplet, in addition to the start and end signals.
- 5 ‘
- AUG – methionine / beginnings
- GAG – Glutamate
- CUU – Leucine
- AGC – Serina
- UAG – STOP
- 3 ‘
The role of ribosomes and tRNA
Before going into the details of how DNA translation is given, we will talk about the two elements that make it possible to read mRNA and to synthesize 1 strand: Ribosomes and transfer RNA.
RNA transfer (tRNA)
Transfer RNA (tRNA) is a type of RNA that serves as a molecular bridge to connect mRNA codons to the amino acids they code for. Without this type of RNA, it would not be possible to link an amino acid to the triplet of nucleotides present in the mRNA..
At each tRNA is an end that has a three-nucleotide sequence, called an 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 that look like two burger doughs.: The large subunit and the small subunit. In the ribosome, furthermore, there are three empty sites where tRNA binds to mRNA: sites A, P and E. It is in ribosomes that polypeptides are constructed.
Large and small subunits come together around mRNA, and through enzymatic action, the ribosome catalyzes a chemical reaction that binds amino acids in tRNA to form a polypeptide chain.
DNA translation: the process
Every second, our cells produce hundreds of proteins. It is for this reason that translation is such an important process for life, because without it we would be deprived of the ability to transform the information in genes into something useful. DNA translation occurs in three stages: initiation, elongation and termination.
Initiation of DNA translation occurs in the ribosome. This organelle attaches itself around an mRNA molecule, from which a tRNA will come.
This latter type of RNA must carry the amino acid methionine, encoded by the AUG codon, which is the signal for initiating the synthesis of the polypeptide chain.
This ribosome-tRNA-mRNA-methionine set is known as the initiation complex and is necessary for translation to occur.
Elongation, as the name suggests, is 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, 1 corresponding tRNA binds. The existing chain of amino acids binds to the amino acid in tRNA through a chemical reaction. The mRNA shifts a codon on the ribosome, exposing a new codon to read.
Within the lengthening, we can distinguish three stages:
In the first, an anticodon, that is to say a tRNA triplet containing the bases complementary to those of an mRNA triplet, Is “paired” with an exposed codon of mRNA at site A.
A peptide bond is formed, by the catalytic action of aminoacyl-tRNA synthetase, between the new amino acid introduced and the one immediately preceding it. The new amino acid is found in the A site of the ribosome, while the previous one is in the P. After forming the bond, the polypeptide is transferred from the P site to the A site.
The ribosome advances a codon in the mRNA. The tRNA at site A carrying the polypeptide moves to site P. It then moves to site I and exits the ribosome.
This process is repeated several times, as many new amino acids are placed if no signal has appeared previously indicating that the continuation of the polypeptide chain should be stopped.
Termination is when the polypeptide chain is released, ceasing to grow. It begins when a stop codon (UAG, UAA or UGA) appears in mRNA. this when introduced into the ribosome, it triggers a series of events that cause the strand of its tRNA to separate., Allowing it to float towards the cytosol.
It may be that, despite completion, the polypeptide still needs to assume the correct three-dimensional shape, so that it becomes a well-formed protein.
Although proteins are essentially polypeptide chains, their difference from the newly made polypeptide chains in the ribosomal complex is that they have a three-dimensional shape, while the new new polypeptide chain is basically a very linear chain of amino acids.
- Pamela C Champe, Richard A Harvey and Denise R Ferrier (2005). Lippincott Illustrated Reviews: Biochemistry (3rd ed.). Lippincott Williams and Wilkins. ISBN 0-7817-2265-9
- David L. Nelson and Michael M. Cox (2005). Lehninger’s Principles of Biochemistry (4th ed.). WH Freeman. ISBN 0-7167-4339-6
- Hirokawa et al. (2006). The ribosome recycling stage: consensus or controversy? Trends in Biochemical Sciences, 31 (3), 143-149.