Question

Answer the following questions:

(a) [(i)] Explain how some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans but do not kill the Bacillus.

[(ii)] How is the above mechanism exploited for the production of Bt cotton plant by biotechnologists?

(b) [(i)] Explain how the amplification of gene of interest is done using PCR.

[(ii)] State two applications of the desired amplified fragment of DNA.

Hint:

Bt cotton is an example of genetic engineering used for pest resistance. PCR revolutionized molecular biology by allowing fast amplification of DNA for multiple applications.

Answer 1

[(i)] Some strains of Bacillus thuringiensis (Bt) produce crystal proteins called Cry proteins. These are toxic to insects like lepidopterans (e.g., bollworms) when ingested. The Cry protein binds to specific receptors in the gut of the insect, causing cell lysis and death. These receptors are absent in Bacillus and in humans, hence they remain unaffected.

[(ii)] Biotechnologists isolate the gene coding for Cry protein from Bt and insert it into the genome of cotton plants. These genetically modified plants express the Cry protein, making them resistant to insect pests like bollworms. This results in reduced pesticide use and better crop yield.

[(i)] Polymerase Chain Reaction (PCR) is a technique used to amplify a specific gene of interest. It involves repeated cycles of denaturation, annealing of primers, and extension by a thermostable DNA polymerase. Billions of copies of the desired gene can be synthesized in a few hours.

[(ii)] Two applications of the amplified DNA fragment are:

Used in DNA fingerprinting and forensic analysis.

Used in diagnostics for detecting genetic disorders or pathogens.