The genetic code contains 61 codons to specify the 20 common amino acids. Many organisms carry fewer than 61 different tRNA genes in their genomes. These genomes take advantage of isoaccepting tRNAs and the rules governing third-base wobble to encode fewer than 61 tRNA genes. Use these rules to calculate the minimal number of tRNA genes required to specify all 20 of the common amino acids.

Key Concepts

Codons and Amino Acids

Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids during protein synthesis. There are 64 possible codons (61 for amino acids and 3 stop codons) that encode for the 20 common amino acids. Understanding the relationship between codons and amino acids is essential for determining how many tRNA molecules are needed for translation.

tRNA and Isoaccepting tRNAs

Transfer RNA (tRNA) molecules are responsible for bringing amino acids to the ribosome during protein synthesis. Isoaccepting tRNAs are different tRNA species that can carry the same amino acid but have different anticodons. This redundancy allows organisms to use fewer tRNA genes than there are codons, as multiple tRNAs can recognize the same amino acid.

Wobble Hypothesis

The wobble hypothesis explains how the third base of a codon can pair loosely with the corresponding base of a tRNA anticodon, allowing for flexibility in base pairing. This means that a single tRNA can recognize multiple codons that code for the same amino acid, reducing the total number of tRNA genes required. This concept is crucial for calculating the minimal number of tRNA genes needed to specify all 20 amino acids.