Question

Why are frameshift mutations likely to be more detrimental than point mutations, in which a single pyrimidine or purine has been substituted?

Short answer

Frameshift mutations are more likely to be detrimental than single purine or pyrimidine substitutions because they cause a shift in the reading frame for translation, leading to significant alterations in the amino acid sequence of the synthesized protein and a higher likelihood of protein dysfunction. This can result in nonfunctional or malfunctioning proteins, which may cause severe problems for the organism. In contrast, point mutations involving single purine or pyrimidine substitutions often have more localized effects, with some not even causing changes in the amino acid sequence, making them less likely to disrupt protein function.

Step-by-step solution

Define Frameshift Mutations and Point Mutations

Frameshift mutations are genetic mutations caused by the insertion or deletion of nucleotides in a DNA sequence, which shifts the reading frame for translation. This can result in a completely different sequence of amino acids in the synthesized protein, often leading to a nonfunctional or malfunctioning protein. On the other hand, point mutations are changes in a single nucleotide in the DNA sequence, either through substitution, insertion, or deletion. In this case, the question specifically refers to substitutions of single purines or pyrimidines. This type of mutation has a more localized effect on the gene, potentially changing a single amino acid or having no effect at all due to redundancy in the genetic code.

Consequences of Frameshift Mutations

Due to the reading frame shift in frameshift mutations, a completely different set of amino acids might be translated from the mutated gene. This might lead to a complete loss of protein function or even the formation of a harmful protein. These mutations often result in truncated proteins, meaning that the premature introduction of a stop codon cuts the protein synthesis short. Truncated proteins are usually nonfunctional and can lead to severe dysfunction in some cases.

Consequences of Point Mutations

Point mutations involving single purine or pyrimidine substitutions may have mild, severe, or no impact on the encoded protein. Cases where the mutation leads to an amino acid with similar properties might not significantly impact protein function. Due to the degenerate nature of the genetic code, some point mutations do not even result in an amino acid change, as multiple codons can code for the same amino acid. In some instances, a point mutation may result in the substitution of an amino acid with significantly different properties, which might affect the protein function. In extreme cases, a point mutation could introduce a premature stop codon, leading to a similar truncation as seen in frameshift mutations. However, the overall probability of these severe outcomes is low compared to frameshift mutations.

Compare the Effects of Frameshift and Point Mutations

While both frameshift and point mutations have the potential to be detrimental to protein function, frameshift mutations are more likely to have severe consequences due to the drastic changes in the amino acid sequence and potential truncation of the protein. In comparison, point mutations are usually limited to changing a single amino acid at most, with some not even having an effect on the amino acid sequence.

Conclusion

Frameshift mutations are likely to be more detrimental than point mutations because they drastically change the reading frame for translation, causing significant alterations to the resulting protein sequence and a higher likelihood of protein dysfunction. In contrast, point mutations involving single purine or pyrimidine substitutions often have localized effects, which may or may not cause amino acid changes and are less likely to result in major disruptions to protein function.