Question

Sydney Brenner argued that the code was nonoverlapping because he considered that coding restrictions would occur if it were overlapping. A second major argument against an overlapping code involved the effect of a single nucleotide change. In an overlapping code, how many adjacent amino acids would be affected by a point mutation? In a nonoverlapping code, how many amino acid(s) would be affected?

Short answer

Answer: In an overlapping code, a point mutation would affect 2 adjacent amino acids, whereas in a nonoverlapping code, it would affect only 1 amino acid.

Step-by-step solution

1. Understanding overlapping and nonoverlapping codes

An overlapping code is when a single nucleotide is part of more than one codon (a sequence of 3 nucleotides that code for a specific amino acid). In contrast, a nonoverlapping code is when a single nucleotide is part of only one codon.

2. Considering point mutations in overlapping codes

In an overlapping code, a point mutation (change in one nucleotide) would affect the amino acid coded by the codon it is a part of, as well as the amino acid(s) encoded by the adjacent codon(s) sharing the mutated nucleotide. This is because the mutated nucleotide is part of more than one codon.

3. Calculating the number of affected amino acids in overlapping codes

Let's consider a point mutation occurs at the second nucleotide of a codon, in an overlapping code: Original: A-T-A | T-G-C Mutation: A-G-A | G-G-C The mutated nucleotide affects two codons and their encoded amino acids because the second nucleotide (T) is part of both the first and second codons (bolded): ATA - Original amino acid 1 *AGA - New amino acid 1 due to mutation* TGC - Original amino acid 2 *GGC - New amino acid 2 due to mutation* So, in an overlapping code, a point mutation would affect 2 adjacent amino acids.

4. Considering point mutations in nonoverlapping codes

In a nonoverlapping code, a point mutation would affect only the amino acid coded by the mutated codon, since that nucleotide is not part of any other codon.

5. Calculating the number of affected amino acids in nonoverlapping codes

Let's consider a point mutation occurs at the second nucleotide of a codon, in a nonoverlapping code: Original: A-T-A | G-C-A Mutation: A-G-A | G-C-A The mutated nucleotide affects only one codon and its encoded amino acid: ATA - Original amino acid 1 *AGA - New amino acid 1 due to mutation* GCA - Unaffected amino acid 2 So, in a nonoverlapping code, a point mutation would affect only 1 amino acid. In summary, in an overlapping code, a point mutation will affect 2 adjacent amino acids, while in a nonoverlapping code, it will affect only 1 amino acid.