What is a frameshift mutation and how can it affect protein function?

• A. Insertions or deletions not in multiples of three shift the reading frame, often creating premature stop codons and nonfunctional or truncated proteins.
• B. A single nucleotide substitution that changes one amino acid but preserves reading frame.
• C. It changes only noncoding regions.
• D. It increases folding complexity with no functional impact.

Answer: (A)

Frameshift mutations happen when nucleotides are inserted or deleted in a coding region in a number not divisible by three. Since the genetic code is read in triplets (codons), shifting the reading frame means every downstream codon changes, so the amino acid sequence after the mutation is altered. This often creates a premature stop codon, producing a truncated, nonfunctional protein. The disruption can affect important domains and overall folding, leading to loss of function. If insertions or deletions occur in multiples of three, the reading frame stays intact (an in-frame indel), so the protein may be longer or shorter but the downstream sequence isn’t shifted.