a single nucleotide deletion during DNA replication: – causes one amino acid of the protein to be incorrect – causes all of the amino acids of the protein to be incorrect – causes the amino acids encoded by nucleotides after the deletion to be incorrect – causes the amino acids encoded by nucleotides before the deletion to be incorrect – has no effect on the resulting protein
The Correct Answer and Explanation is :
The correct answer is: causes the amino acids encoded by nucleotides after the deletion to be incorrect.
Explanation
A single nucleotide deletion during DNA replication results in a frameshift mutation, which alters the reading frame of the genetic code. The genetic code is read in triplets, known as codons, with each codon specifying a particular amino acid. When one nucleotide is deleted, all downstream codons (the codons that follow the point of deletion) are shifted left by one position.
For example, consider a DNA sequence represented as follows:
Original Sequence:
5′ – ATG GCT ACG TGA – 3′
This translates to the following amino acids (using a simple codon table):
Amino Acids:
Met (ATG) – Ala (GCT) – Thr (ACG) – Stop (TGA)
If a single nucleotide deletion occurs at the first position (e.g., deleting the “A” in ATG), the sequence becomes:
Modified Sequence:
5′ – TG GCT ACG TGA – 3′
Now, the codons are read as:
New Codons:
TGG – CTA – CGT – A (which translates to)
Trp (TGG) – Leu (CTA) – Arg (CGT) – and continues until it hits the stop codon.
As a result, every amino acid encoded after the deletion is likely to be different from the original sequence. This can have significant effects on the protein’s structure and function, potentially rendering it nonfunctional or even harmful.
In contrast, the amino acids encoded by nucleotides before the deletion remain unchanged, as they are still being read by the same codons. However, the subsequent amino acids become increasingly altered due to the new reading frame created by the deletion. In summary, a single nucleotide deletion primarily affects the amino acids downstream of the deletion point, leading to a potentially nonfunctional protein.