Question

Answer the following questions:

[(i)] Explain why the insecticidal protein produced by Bacillus thuringiensis does not kill the bacteria itself.

[(ii)] How has man exploited this protein to produce cotton bollworm-resistant Bt cotton plant?

[(i)] Identify the selectable markers labelled as ‘a’ and ‘b’ in the given diagram of E. coli vector.

[(ii)] How is the coding sequence of enzyme \(\beta\)-galactosidase considered a better marker than the ones identified by you in the diagram? Explain.
[(iii)] List any two uses of cloning vectors in biotechnology.

Hint:

The Bt toxin gene works only inside insect gut as it requires an alkaline pH for activation, thus remaining harmless to the bacteria itself.

Answer 1

[(i)] The protein produced by Bacillus thuringiensis is in inactive form (protoxin) inside the bacteria. It becomes active only in the alkaline gut of insects.
[(ii)] The gene coding for this protein has been incorporated into cotton plants. This makes Bt cotton produce the insecticidal protein, which kills bollworm pests on consumption.
[(i)] In the diagram of pBR322 vector:

‘a’ is amp$^{r}$ gene (ampicillin resistance)

‘b’ is tet$^{r}$ gene (tetracycline resistance)

[(ii)] The \(\beta\)-galactosidase gene produces a visible colour change when active. This allows for blue-white screening, a simpler and faster method to identify recombinant colonies.
[(iii)] Uses of Cloning Vector:

For producing multiple copies of a specific gene.
For transferring desirable genes into host organisms.