Question

- Describe what happens to a protein produced as a result of a point mutation.


- Describe what happens to a protein produced as a result of a frameshift mutation.


- Which type of mutation is most likely to result in a functional protein? Explain.

Answer 1

- Protein from a point mutation
- A point mutation is a single-base substitution. Its effects on the protein depend on the codon change:
- Silent (synonymous) — the codon still encodes the same amino acid → protein sequence and function usually unchanged.
- Missense (nonsynonymous) — one amino acid is replaced by another. Outcome ranges from benign (if the substitution is conservative or occurs in a non‑critical region) to harmful (if it disrupts an active site, folding, stability, or interactions). It can also occasionally produce a new or harmful function.
- Nonsense — the substitution creates a stop codon → truncated protein that is usually nonfunctional and often degraded (e.g., by nonsense‑mediated decay).
- The effect also depends on location (active site, structural core, targeting sequences, splice sites) and on whether the change alters mRNA stability or splicing.

- Protein from a frameshift mutation
- A frameshift results from insertion or deletion of nucleotides not in multiples of three. It changes the reading frame from the mutation onward, so:
- Every downstream codon is altered, producing a run of incorrect amino acids.
- A new premature stop codon is commonly encountered, yielding a truncated, typically nonfunctional protein that is often unstable or degraded.
- Frameshifts almost always cause severe loss of normal protein function; in rare cases they may create a different functional product, but that is uncommon.

- Which is more likely to yield a functional protein?
- Point mutations are far more likely to produce a functional protein than frameshift mutations. Reason: a point change affects at most one amino acid (and can be silent or conservative), whereas a frameshift alters the entire downstream amino‑acid sequence and frequently introduces an early stop codon. (Exceptions exist: a point mutation that creates a nonsense codon or disrupts a critical residue can be catastrophic; an in‑frame indel of three bases is not a frameshift and can be tolerated.)