What is tRNA?


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Transfer Ribonucleic Acid

tRNA is a nucleic acid that is involved in protein synthesis - specifically translation. When mRNA arrives in the cytoplasm, the large and small subunits of the ribosome come together and attach to the mRNA. The codons (three nitrogen bases of mRNA) are read and matched up with the anti-codons (complementary three bases to mRNA) of tRNA. Each codon codes for one amino acid, though one amino acid may code for many codons.

The ribosome has three grooves which are holding sites for the tRNA. The first codon is AUG, called a "start codon". It also codes for the amino acid Met (methionine). So tRNA with the anti-codon sequence of UAC carrying the amino acid Met bonds to the mRNA codon. Another tRNA bonds to the next codon in the next groove with the next respective amino acid. Peptidyl transferase breaks the bond between the tRNA and the first amino acid and then reforms a peptide bond between the first amino acid and the second. This elongation process repeats until a long chain of amino acids is formed, creating a polypeptide. The tRNA exits the ribosome on the "E" site and returns to the cytoplasm. It will then pick up another of the same amino acid from the pool of amino acids stored in the cytoplasm and return to translation.

In two dimensions, tRNA has three loops, one of which is the anti-codon. Opposite the anti-codon is the amino acid attachment site. In three dimensions, tRNA is "L" shaped; bent in the middle. See related links below for images.