Which types of RNA are involved in protein synthesis?

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mvcdc eNotes educator| Certified Educator

Proteins are chains of amino acids of varying length that perform crucial roles in the body and enable life to happen. Synthesis of proteins is controlled at the DNA level - i.e. the sequence of amino acids in the protein which determines, in a way, its structure and hence function, is dictated by the sequence in the DNA bases. An amino acid corresponds to a codon - three consecutive bases in a DNA. For example ATG corresponds to methionine in the protein. Protein synthesis, however, does not directly use DNA, but uses RNA.

RNA is also a sequence of bases, not very different from DNA except for a few things. Instead of the base thymine (T), RNA has uracil (U). Also, the sugar contains an extra OH group (the D in DNA stands for deoxy). DNA is first transcribed into mRNAs (messenger RNAs). Transcription involves the 'copying' of genetic information from the DNA. The mRNA is single stranded. Ultimately, this mRNA is what gets translated into the amino acid sequence of the protein (in this case, for example, methionine is encoded from AUG, as T is replaced by U).

The mRNA is then 'read' and codons are translated to amino acids. The translation of the three-base codon to the amino acid is done by tRNAs (transfer RNAs). tRNAs have a conserved structure. They contain an anti-codon to the mRNA sequence. The anti-codon matches with the codon, and that is how the mRNA is 'read.' For instance, the AUG codon matches with the UAC anti-codon. At one end of the tRNA, a base is attached via an ester bond (see attached image). Each amino acid has one or more tRNAs dedicated to it, and each of these tRNA will have the corresponding anti-codon. For instance, the tRNA for M will have M attached on it via an ester bond, and an anti-codon sequence (UAC) that is complementary to the M codon (ATG). As the mRNA is read, tRNAs sequentially come in, and the amino acids are linked together via peptide bonds as their ester bond to the tRNA is cleaved.

Protein synthesis occurs in the ribosomes. Ribosomes are cell structures that contain proteins and rRNAs (ribosomal RNAs). These protein-RNA complexes are what moves along the mRNA, that catalyzes the formation of the bonds between the amino acids.

In brief:

There are three types of RNAs that are mainly involved in protein synthesis - mRNA, which carries the genetic material to be translated to the amino acid sequence, tRNA which allows for the translation of the codon into amino acid by bringing in the amino acid corresponding to that codon, and rRNA, which comprises the ribosome where protein synthesis occurs.

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