The mechanism of translation of mRNA to proteins
The translation is similar in prokaryotes and eukaryotes, but there is some difference. For example, the mRNA of prokaryotes does not need maturation, so as it is synthesized, it is read by ribosomes to translate its information into amino acids of a protein.
In contrast, in eukaryotic cells, the primary transcribed mRNA is synthesized in the nucleus and has to undergo a maturation process before becoming functional RNA that traverses the pores of the nuclear membrane into the cytoplasm. Then, in the rough endoplasmic reticulum or in the cytosol, ribosomes will translate their information into proteins.
The following stages are distinguished in the biosynthesis of proteins:
- Activation of amino acids or formation of the amino acid-transfer RNA complex.
- Elongation of the polypeptide chain.
- Association of several polypeptide chains and, sometimes, prosthetic groups, to constitute proteins.
Before starting protein synthesis, it is necessary for the amino acid to be activated, binding to the CCA triplet of tRNA. The aminoacyl-tRNA synthetases enzymes are specific for each amino acid, and are responsible for making this union, but the energy provided by the hydrolysis of ATP is necessary. There are 20 aminoacyl-tRNA-synthetase, one for each amino acid. These enzymes are very specific, as they have to bind each amino acid to the corresponding tRNA.
The amino acid joins at its carboxyl end (-COOH) to the 3' end of the tRNA (specifically, to the hydroxyl group (-OH) of the 3' carbon of the last nucleotide, which always carries adenine), and is renamed aminoacyl-tRNA.
Amino acid + ATP + tRNA ↔ aminoacyl-tRNA + AMP + PPi
As you may recall, tRNA molecules have four arms: D, T, amino acid acceptor, and anticodon.
The 3' and 5' ends of the chain are located on the amino acid acceptor arn:
- At the 3' end, the CCA triplet always appears, to which the amino acid binds.
- The 5' end always ends with a guanine nucleotide.
The tRNA molecules are the intermediaries between the nucleotide sequence of the mRNA and the amino acid sequence, since, in addition to providing the amino acid attached to their 3' end, they are responsible for recognizing the RNA codon complementary to its anticodon.
When the aminoacyl-tRNAs have already been formed, protein synthesis occurs. The process is carried out in three stages: