Explain that a gene mutation is a result of substitution or deletion or insertion of nucleotides in DNA and outline how each of these types of mutation may affect the polypeptide produced

Sourav PanOctober 29, 2024

Answered

Gene mutations can arise from various alterations in the nucleotide sequence of DNA, primarily through substitution, deletion, or insertion of nucleotides. Here’s an explanation of each type of mutation and how they may affect the resulting polypeptide:

1. Substitution Mutations

• Definition: A substitution mutation occurs when one nucleotide in the DNA sequence is replaced by another nucleotide. This can involve changing one base for another, resulting in a different codon.
• Types:
  • Silent Mutation: If the substitution does not change the amino acid due to the redundancy of the genetic code (e.g., changing UUA to UUG, both of which code for leucine), the polypeptide remains unchanged.
  • Missense Mutation: If the substitution results in a different amino acid (e.g., changing AUC to GUC, which changes isoleucine to valine), this can alter the protein’s structure and function, potentially impacting its activity.
  • Nonsense Mutation: If the substitution creates a premature stop codon (e.g., changing UAC to UAA), this results in a truncated protein that is usually nonfunctional.

2. Deletion Mutations

• Definition: A deletion mutation occurs when one or more nucleotides are removed from the DNA sequence. This can shift the reading frame of the codons downstream from the deletion.
• Effects on Polypeptide:
  • Frameshift Mutation: The removal of nucleotides can lead to a shift in the reading frame, changing how the codons are read. For example, if three nucleotides (one codon) are deleted, the reading frame may be preserved, but the polypeptide may still lack that specific amino acid, potentially altering its structure and function.
  • If one or two nucleotides are deleted, the entire reading frame shifts, resulting in completely different amino acids being incorporated downstream, which often produces a nonfunctional protein.

3. Insertion Mutations

• Definition: An insertion mutation occurs when one or more nucleotides are added to the DNA sequence, which can also shift the reading frame of the codons.
• Effects on Polypeptide:
  • Frameshift Mutation: Similar to deletions, inserting one or two nucleotides leads to a shift in the reading frame, resulting in the incorporation of incorrect amino acids and potentially leading to a nonfunctional protein.
  • If three nucleotides are inserted (one codon), the reading frame remains intact, but the additional amino acid can alter the protein’s structure and function, which may affect its activity.