Question

You perform an experiment in which you add a synthetic mRNA to a test tube that contains all components required for translation (it was just lacking the mRNA). You find that a polypeptide consisting of 122 amino acids is produced. Then you perform another experiment, this time adding the mRNA from a mutant version of the gene and find that a polypeptide consisting of 48 amino acids was produced. What is a likely explanation for this observation?

	A.	The mutant version of the gene must have a frameshift mutation upstream of the promoter, therefore a truncated protein is produced.
	B.	The mutant version of the protein has a frameshift mutation close to the 3' end of the protein coding region, so that a truncated version of the protein is produced.
	C.	The mutant version of the gene has a nonsense mutation, so that a truncated protein is produced.
	D.	The mutant version of the gene has a synonymous mutation so that a truncated version of the protein is produced.

Answer 1

Answer:

Frameshift mutations lead to a change in the frame of how codons are read by translation machinery. This generally leads to a change in amino acid sequence of the protein.

Non-sense mutations are those which lead to generation of a "stop-codon". Stop codons are those which lead to termination of translation and the size of protein gets reduced.

Synonymous mutations do not lead to any change in the message encoded by a codon.

It is given that from 122 amino acids, protein size was reduced to 48 amino acids in the mutant. This can be most likely due to a non-sense mutation.

Hence, correct choice should be:

c	The mutant version of the gene has a nonsense mutation, so that a truncated protein is produced.