Question

Western blotting is a technique that can detect a specific polypeptide using an antibody probe. In a Western blotting experiment, a mixture of cellular proteins is separated using gel electrophoresis according to their molecular masses. After the antibody has bound to the protein of interest within a blot of a gel, the protein is visualized as a dark band. In this example, an antibody is used to detect the presence, size, and quantity of B-globin polypeptide in a Western blot using three samples: a normal red blood cell sample (lane 1), a kidney sample (lane 2), and a red blood sample from a patient with the genetic disorder B-thalassemia (lane 3). Western blot 1 2 3 15.9 kDa 10.1 kDa Figure 2. Western Blot detecting B-globin from three genetically distinct individuals. Lane 1 shows a sample of proteins isolated from normal red blood cells. Lane 2 shows a sample of proteins isolated from kidney cells which do not produce B-globin. Lane 3 shows a sample of proteins isolated from a red blood cell of an individual with B-thalassemia (a genetic blood disorder due to mutated B-globin).

Based on the data above, the individual in lane 3 most likely has which of the following types of mutations in β-globin?

Group of answer choices

- Nonsense mutation

- Missense mutation

-Trinucleotide repeat expansion

-Silent mutation

-Back mutation

Answer 1

Nonsense Mutation

If we compare the molecular mass of the normal band with that of the mutated band on the gel, then we can see that the mass of the mutated band is less than that of the normal Band. It may be because of the fact that some of the nucleotides are absent in the mutated band. And this is possible if the mutation is a nonsense mutation. This is because a nonsense mutation leads to the formation of a premature stop codon leading to the premature termination of translation and formation of truncated peptide.

There will be almost no change in the mass of the mutated band if it was missense mutation or silent mutation.

If this was a trinucleotide repeat expansion, then the molecular mass of the mutated band would have increased because expansion leads to addition of nucleotides.

This cannot be back mutation because back mutation leads to the Restoration of the original phenotype and hence there would have been no difference in the mass of Band in the mutated and the normal ones.

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