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 overlapping genetic codes, a point mutation potentially affects two adjacent amino acids. In nonoverlapping genetic codes, a point mutation affects only one amino acid.

Step-by-step solution

Define overlapping and nonoverlapping codes

In a genetic code, the codons are sequences of three nucleotides. The difference between overlapping and non-overlapping codes lies in how contiguous codons are organized in the gene. - In an overlapping code, a single nucleotide can be a part of two or more codons. - In a nonoverlapping code, each nucleotide belongs to only one codon, and codons are read consecutively, without overlap.

Determine the effect of a point mutation on overlapping code

In an overlapping code, a single nucleotide change in any of the codons will impact both the codon where the mutation occurred, as well as any adjacent codons that share the mutated nucleotide. Thus, if we have the sequence "ABCDEF" where letters represent nucleotides, a mutation in nucleotide "C" would affect both the ABC and CDE codons. Since a single codon corresponds to one amino acid, this means that a point mutation in an overlapping code will potentially affect two adjacent amino acids.

Determine the effect of a point mutation on nonoverlapping code

In a nonoverlapping code, each nucleotide is only a part of a single codon. Therefore, a point mutation will only affect the single codon where the mutation took place. As a result, only one amino acid would be impacted by this mutation.

Answering the questions

In an overlapping code, a point mutation will potentially affect two adjacent amino acids due to nucleotide(s) being shared by adjacent codons. In a nonoverlapping code, a point mutation will affect only one amino acid, as each nucleotide belongs to only one codon.

Key concepts

Nonoverlapping Code

In the genetic world, a nonoverlapping code is a system where each nucleotide in a DNA sequence is a part of only one codon. Codons, which are groups of three nucleotides, are read from start to finish, without any of the nucleotides overlapping with others. This simplicity is critical for accurately translating genetic information into proteins. Since each nucleotide contributes to only one codon, any change in the sequence impacts just one codon and, consequently, one amino acid.

For example, if we have the DNA sequence "ATGCCG," the first codon is "ATG," and the second one is "CCG." A mutation in the middle nucleotide of "ATG" would only affect "ATG," ensuring that "CCG" remains unchanged. This is how nature keeps potential errors from cascading across multiple amino acids, preserving the functional integrity of proteins.

Overlapping Code

The overlapping code is an interesting theoretical format where each nucleotide could be a part of multiple codons. This can be visualized by imagining a sliding window across a sequence. In overlapping codes, the boundaries between codons are blurred, meaning that the last nucleotide of one codon might also be the first nucleotide of the next.

Consider a sequence "ABCDEF," where "ABC," "BCD," and "CDE" could all be codons. If there is a mutation in "C," it affects not just one, but all the codons it participates in: "ABC," "BCD," and "CDE." Consequently, this type of coding would mean one point mutation could lead to changes in several different amino acids, which could be detrimental. While overlapping codes allow for more compact genetic material, they are not favored in nature due to complexity and potential for error propagation.

Point Mutation Effect

A point mutation is a single nucleotide alteration in a DNA sequence, which could potentially lead to changes in the protein produced by that sequence. The effect of such a mutation depends heavily on whether the genetic code is overlapping or nonoverlapping.

In a nonoverlapping code, the impact of a point mutation is limited to a single codon and its corresponding amino acid. This scenario isolates the mutation's effect, preventing widespread protein malfunction.

• Single nucleotide alteration affects one codon.
• The result is a change in only one amino acid.

Conversely, in an overlapping code, a point mutation might have a ripple effect. Since nucleotides belong to multiple codons, one small mutation could alter multiple amino acids, leading to more drastic changes in the protein structure.

• Mutation can alter several codons.
• Potentially affects two or more amino acids.

Understanding the effect of point mutations helps in appreciating why nature has predominantly chosen a nonoverlapping scheme to minimize the risk of error during genetic translation.