Several lines of experimental evidence pointed to a triplet genetic code. Identify three pieces of information that supported the triplet hypothesis of genetic code structure.

Verified step by step guidance

1. Understand that the triplet genetic code hypothesis proposes that three nucleotide bases (a codon) specify one amino acid in a protein sequence.
2. Consider the experimental evidence from frameshift mutations, where insertions or deletions of one or two nucleotides cause a shift in the reading frame and drastically alter the protein, but insertions or deletions of three nucleotides often restore the reading frame, supporting the idea that codons are triplets.
3. Examine the work of Crick and Brenner, who showed that adding or removing three nucleotides (or multiples of three) in bacteriophage genes could restore function, indicating that the genetic code is read in sets of three nucleotides.
4. Look at the biochemical evidence from synthetic RNA experiments (e.g., Nirenberg and Matthaei), where specific trinucleotide sequences were shown to direct the incorporation of specific amino acids during protein synthesis, confirming that codons are triplets.
5. Review the fact that the number of possible triplet codons (4³ = 64) is sufficient to code for all 20 amino acids plus stop signals, which aligns with the observed complexity of the genetic code.

Key Concepts

Frameshift Mutations and Their Effects

Frameshift mutations, caused by insertions or deletions of nucleotides, disrupt the reading frame of mRNA. Experimental evidence showed that adding or removing three nucleotides often restored the original reading frame, supporting the idea that the genetic code is read in triplets.

Crick, Brenner, and Colleagues’ Experiments

The experiments by Crick and colleagues using bacteriophage T4 demonstrated that mutations in multiples of three nucleotides could restore protein function. This indicated that codons consist of three nucleotides, as changes in triplets preserved the downstream reading frame.

Triplet Codon Specificity in Protein Synthesis

Early biochemical studies showed that each amino acid is encoded by a sequence of three nucleotides (a codon). This triplet nature explained how 20 amino acids could be specified by combinations of four nucleotides, providing a logical framework for the genetic code.