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)] Certain strains of Bacillus thuringiensis (Bt) generate crystal proteins, known as Cry proteins, which are insecticidal to lepidopterans (e.g., bollworms) upon ingestion. The Cry protein attaches to specific gut receptors in insects, leading to cell lysis and mortality. These receptors are absent in Bacillus and humans, ensuring their immunity.

[(ii)] Biotechnologists extract the Cry protein gene from Bt and introduce it into cotton plant genomes. These genetically modified cotton plants produce the Cry protein, conferring resistance to pests like bollworms, thereby reducing pesticide application and improving crop yields.

[(i)] Polymerase Chain Reaction (PCR) is a method for amplifying specific DNA sequences. It employs cyclical denaturation, primer annealing, and extension by a heat-stable DNA polymerase, generating billions of gene copies within hours.

[(ii)] Amplified DNA fragments have two primary applications:

Application 1: Employed in DNA fingerprinting and forensic investigations.

Application 2: Utilized in diagnostic tests for identifying genetic disorders or pathogens.