Question

Protein sequence A: MGPLVPRGSMALIVLGGVAGLLLFIGLGIFFSVRSRHRRRQAERMSQIKRLLSEKKTSQSPHRFQKTHSPI

DNA sequence B:
ATGGGCCCGCTGGTGCCGCGCGGCAGCATGGCGCTGATT
GTGCTGGGCGGCGTGGCGGGCCTGCTGCTGTTTATTGGC
CTGGGCATTTTTTTTAGCGTGCGCAGCCGCCATCGCCGC
CGCCAGGCGGAACGCATGAGCCAGATTAAACGCCTGCTG
AGCGAAAAAAAAACCAGCCAGAGCCCGCATCGCTTTCAG
AAAACCCATAGCCCGATT

Primer Sequence C:
5’ CTGCTGCTGTTTATTGGC 3’

The first 20 amino acids in ‘Protein sequence A’ form a transmembrane helix. The remainder of the protein forms a globular cytoplasmic domain.

(i) Without copying out any sequence, describe the product you would expect to generate from a PCR reaction using ‘Primer sequence C’ as the forward primer, ‘DNA sequence B’ as the template and a reverse primer that matches the end of ‘DNA sequence B’? (2 marks)

(ii) Describe, without sequence, the protein this would encode. (2 marks)

(iii) Suggest a reason for cloning this product. (3 marks)

Answer 1

PCR is a technique used to amplified DNA fragments. For that, primer must be complement with a part of the DNA sequence. Two primers are necessary: a forward primer and a reverse primer. These two primers mark the beginning and the end of the DNA sequence to be copied.

In the example, primer sequence C does not much with DNA sequence B. As reverse primer does match the end of DNA sequence B, the final result of PCR would be copies of all the sequence. During PCR, enzyme would use reverse primer to copy all the DNA sequence B, without the limitation of the forward primer.