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.

Verified step by step guidance

1. Understand the concept of codons and tRNAs: Codons are sequences of three nucleotides that specify amino acids. There are 61 codons for amino acids, but due to the degeneracy of the genetic code, multiple codons can specify the same amino acid. tRNAs are molecules that match codons with their corresponding amino acids during translation.
2. Learn about isoaccepting tRNAs: Isoaccepting tRNAs are different tRNA molecules that carry the same amino acid but recognize different codons. This reduces the number of distinct tRNA genes required in the genome.
3. Understand the wobble hypothesis: The wobble hypothesis explains that the third base of a codon can form non-standard base pairs with the first base of the anticodon in tRNA. This allows one tRNA to recognize multiple codons, further reducing the number of tRNA genes needed.
4. Determine the minimal number of tRNA genes: To calculate the minimal number of tRNA genes, consider the number of codons for each amino acid and how many of these can be recognized by a single tRNA due to wobble pairing. For example, codons ending in U or C can often be recognized by the same tRNA, and codons ending in A or G can be recognized by another tRNA.
5. Sum the minimal number of tRNAs required for all amino acids: For each of the 20 amino acids, calculate the minimum number of tRNAs needed based on the wobble rules and isoaccepting tRNAs. Add these numbers together to find the total minimal number of tRNA genes required to specify all 20 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 (including stop codons), but only 20 common amino acids. This redundancy in the genetic code allows for multiple codons to code for the same amino acid, which is crucial for understanding how fewer tRNA genes can still specify all amino acids.

tRNA and Isoaccepting tRNAs

Transfer RNA (tRNA) molecules are responsible for bringing amino acids to the ribosome during translation. Isoaccepting tRNAs are different tRNA species that can carry the same amino acid but have different anticodons. This allows a single amino acid to be encoded by multiple tRNA genes, reducing the total number of tRNA genes needed in an organism's genome.

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 differ in their third nucleotide, further decreasing the number of tRNA genes required to translate the genetic code into proteins.