Question

How can a mutation that retains an intron's sequence and a triplet repeat mutation have a similar effect on a gene's encoded protein?

Short answer

Both a mutation that retains an intron and a triplet repeat mutation can cause changes to a protein's structure and function. This is because they both cause errors in the sequence of amino acids in the protein: the mutation that retains the intron may add extra amino acids or cause a reading frame shift, while the triplet repeat mutation leads to the repetition of an amino acid, both of which can disrupt the protein's form and function.

Step-by-step solution

Understanding Introns and Mutations

Introns are regions in the DNA sequence that do not code for proteins. During transcription, both the coding regions (exons) and non-coding regions (introns) are initially transcribed into RNA. Post transcription, the introns are spliced out of the RNA sequence during pre-mRNA splicing, and the exons are joined together to form a continuous coding sequence. However, when a mutation retains an intron's sequence, this splicing does not occur properly, leading to the inclusion of the intronic sequence in the final mRNA. This can lead to a shift in the reading frame or inclusion of extra amino acids, affecting the protein's structure and function.

Understanding Triplet Repeat Mutations

A triplet repeat mutation occurs when a sequence of three nucleotides is repeated a larger number of times than normal in the gene's DNA. This can lead to the abnormal repetition of an amino acid in the encoded protein, resulting in a protein with altered structure and function.

Comparing the Effects on the Gene's Encoded Protein

Both mutations result in a protein product with an incorrect sequence of amino acids. For the mutation that retains an intron, it may add extra or incorrect amino acids or cause a reading frame shift, leading to erroneous translation of the protein. The triplet repeat mutation also adds additional amino acids, altering the structure of the protein. Therefore, both types of mutation can have similar impacts on the encoded protein's structure and function potentially leading to a non-functioning or deleterious protein.