center Genotype and Phenotype

- tRNA -

Transfer RNA (tRNA) ...
... molecules are short linear sequences of highly modified RNA. Most tRNA molecules are about 76 nucleotides in length, but they range from 60 to 95.

The tRNA molecules fold into a cloverleaf secondary structure that is held in shape by base pairing in at least four regions. This produces four stems or arms and three loops.

Amino acids are covalently joined to the 'stem' or arm of the molecule that is not looped.

Nine hydrogen bonds hold the molecule into an 'L' shaped tertiary structure (shown on the right above). The anticodon is on a loop at the opposite end of the molecule to the amino acid binding region.

tRNA molecules become 'charged' or aminoacylated in a two step reaction in which an enzyme first attaches most of a ATP molecule (AMP) to the amino acid to create a temporary intermediate. In the second step the tRNA molecule displaces the AMP from the amino acid and joins with it, forming an amino acid - tRNA complex.

The enzymes recognize unique features on every different tRNA molecule and will only join the correct amino acid to the correct tRNA.

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Science at a Distance
© 1997, 1998, 1999, 2000 Professor John Blamire