Biology 9700 · AS & A Level · Principles of genetic technology

Principles of genetic technology — practice question

The artificial plasmid pBR322 was designed to function as a vector. It has frequently been used to transfer human genes, for example the human insulin gene, into the bacterium Escherichia coli. This plasmid was made with two genes, each conferring resistance to a different antibiotic: an ampicillin resistance gene and a tetracycline resistance gene. It also contains a recognition site for the restriction enzyme, BamHI, positioned in the centre of the tetracycline resistance gene. A pBR322 plasmid was cut with BamHI and the cDNA gene for human insulin was inserted into it. Fig. 2.1 shows pBR322 and the recombinant plasmid.
(a)[4]

With reference to Fig. 2.1, describe the method by which a cDNA human insulin gene can be inserted into pBR322 after it has been cut by BamHI.

(b(i))[3]

Explain why the bacteria were initially plated on ampicillin-containing agar.

(b(ii))[3]

Explain why, when identifying bacteria that have successfully taken up the recombinant plasmid, it matters that on pBR322 the BamHI target site is located in the middle of the tetracycline resistance gene.

(b(iii))[1]

Use a label line together with the letter $C$ to pick out, on Fig. 2.2, a bacterial colony containing the recombinant plasmid. Place your answer on Fig. 2.2 on page 5.

(c(i))[2]

Explain why antibiotic resistance genes are now seldom used.

(c(ii))[2]

State one kind of gene that has taken the place of antibiotic resistance genes in plasmid vectors and say how its presence can be detected.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Sticky ends are formed” …

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI