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10.6. Translation or protein biosynthesis

Protein translation or synthesis

The DNA is transcribed in the nucleus and the mRNA is formed it contains all the information needed to synthesize proteins in the cytoplasm.

Protein biosynthesis is called translation, since a language change occurs, going from a nucleotide sequence to an amino acid sequence.

The mRNA carries this information to the ribosomes, where the translation will take place, going from the language of nucleic acids (combinations of four letters: A, U, C and G) to the language of proteins (combinations of twenty amino acids). It is the ribosomes that read the nitrogenous bases of the mRNAs and translate them into amino acids.

The nucleotide sequence of the mRNA is divided, three by three, forming triplets or codons. Each of these triplets encodes a specific amino acid. The ribosome and tRNA molecules translate this code to produce proteins. The correspondences between each codon (triplet) and amino acid are determined by the genetic code. It is the tRNA molecules that actually establish these correspondences, since:

  • Each tRNA is bound to a specific amino acid.
  • In one of their arms they have an anticodon, a triplet complementary to the codon of the mRNA.

The translation is done in two phases:

  • The  aminoacyl-tRNA synthetases enzymes are responsible for recognizing a specific amino acid (20 different enzymes, one for each amino acid) and a sequence of bases of the tRNA close to the point where the amino acid will bind. These sequences are characteristic for each amino acid and different from the anticodon. These enzymes allow each amino acid to bind with its tRNA.
  • Then, the tRNA with its amino acid binds, through its anticodon, to the corresponding codon of the mRNA. The ribosome is what allows this binding to take place.