Question

A frameshift mutation from nucleotide insertion at position 4 of a 900-base mRNA is observed. What is the likely outcome?

• A. No change in the final protein
• B. Partial protein production
• C. Complete change in protein production
• D. No change due to RNA editing

Hint:

Frameshift mutation early in a coding sequence usually has a severe effect because all downstream codons change.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
A single nucleotide is inserted at the 4th position of an mRNA sequence.
We need to determine the effect of this mutation on the resulting amino acid sequence.
Step 2: Detailed Explanation:

The Triplet Code: mRNA is read in groups of three nucleotides called codons. Each codon specifies one amino acid.

Frameshift Mutation: When a number of nucleotides not divisible by three (in this case, 1) is inserted, it shifts the entire reading frame for all subsequent codons.

Analyzing the Mutation Site: The mutation occurs at position 4.

The first codon (positions 1, 2, 3) remains intact.

However, because of the insertion at position 4, the second codon (formerly 4, 5, 6) now consists of the inserted base and the original 4th and 5th bases.

Downstream Effect: Every single codon from position 4 to the end of the 900-base sequence is now altered.

Outcome: Since the mutation happened at the very beginning of a long protein (900 bases = 300 amino acids), nearly 99% of the protein will consist of completely different amino acids compared to the original sequence.

Often, frameshifts also result in the early appearance of a stop codon, but the hallmark is a "complete change" in the protein's primary structure.

Step 3: Final Answer:
An insertion at position 4 disrupts the triplet reading frame for almost the entire protein, leading to a complete change in protein production.