Question

The following sequences show the wildtype and mutant alleles of part of a gene. What is the name of this type of mutation?

Wildtype DNA:       5’           AAC – AGC – CTG – CGT – ACG – GCT – CTC 3’

Wildtype protein: Asn – Ser – Leu – Arg – Thr – Ala – Leu

Mutant DNA:          5’ AAC – AGC – CTG – CTT – ACG – GCT – CTC 3’

Mutant protein: Asn – Ser – Leu – Leu – Thr – Ala – Leu

Select one:

a. Frameshift mutation

b. Silent mutation

c. Missense mutation

d. Antisense mutation

What effect will a nonsense mutation in a coding triplet have on the encoded protein?

Select one:

a. Replacement of the affected amino acid with a different amino acid

b. No change to the amino sequence

c. Loss of the affected amino acid but retention of all remaining amino acids downstream of mutation

d. Loss of the affected amino acid and all other amino acids downstream of the mutation site

Once a polypeptide is produced by translation, which cellular organelle is it transported into for correct folding?

Select one:

a. The nucleus

b. The ribosome

c. The endoplasmic reticulum

d. The Golgi

Which two techniques can be used to generate many identical copies of one specific DNA sequence?

Select one:

a. i) Digestion of DNA with Restriction enzymes; and ii) ligation with DNA ligase

b. i) Polymerase chain reaction; and ii) Transformation of bacteria with a recombinant DNA plasmid

c. i) Digestion of DNA with Restriction enzymes; and ii) Transformation of bacteria with a recombinant DNA plasmid

d. i) Polymerase chain reaction; and ii) digestion of DNA with Restriction enzymes

Answer 1

Answer: c. Missense mutation

[Missense mutation is caused when one codon is changed into another codon that codes for a different amino acid. In this case, Arg is replaced by Leu after the mutation.

Other options are incorrect because: Silent mutations are changes in a codon that still codon for the same amino acid. Missense mutation occurs when a codon for any amino acid is mutated into a stop-codon which causes premature termination os translation. There exists no such mutation as antisense mutation]

Answer: d. Loss of the affected amino acid and all other amino acids downstream of the mutation site

[Missense mutation changes a codon to stop codon. Thus, a truncated peptide is formed beyond the point of this mutation due to premature termination of protein synthesis]

Answer: c. The endoplasmic reticulum

[After the synthesis of peptide/protein, it is transported to the Endoplasmic reticulum which is the main site of protein folding for secreted proteins, membrane proteins, etc. Golgi is the main site for glycosylation, which is a covalent post-translational modification. Nucleus is the organelle containing DNA and folding does not occur there. The ribosome is the machinery required during protein synthesis and not during folding.]

Answer: d. i) Polymerase chain reaction; and ii) digestion of DNA with Restriction enzymes

[The DNA sequence to be modified is amplified using sequence specific primers which also contain the site of restriction enzyme. This is followed by digestion of the amplicons using restriction enzymes for further ligation into vectors]

_________________________

[Kindly give a thumbs up]