Applications Of Biotechnology

[(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.

(a) Step 1: Step 4 involves producing multiple copies of the recombinant DNA.
Step 2: The correct technical term for this process is cloning.
Step 3: Cloning allows amplification of the gene of interest inside the host cell.
(b) Step 1: To ligate both vector and foreign DNA, compatible ends are required.
Step 2: If different enzymes (like EcoR I and Hind III) are used, the ends will not match and ligation will be unsuccessful.
Step 3: Therefore, the correct option is (ii): EcoR I to cut both the plasmid and alien DNA.
Step 4: Using the same restriction enzyme ensures that both DNA fragments have complementary sticky ends that can easily join.

Plasmid pBR322 and Its Cloning Sites

The plasmid pBR322 is a widely used E. coli cloning vector. It contains several restriction enzyme recognition sites that can be used for inserting foreign DNA. The rop gene in pBR322 codes for proteins involved in the replication of the plasmid.

The restriction enzyme Pvu II has a unique recognition site within the rop gene of pBR322. Insertion of foreign DNA at this site would disrupt the rop gene function, potentially affecting the plasmid copy number. The other restriction enzymes listed (Pst I, EcoR I, BamH I) have cloning sites in different regions of the pBR322 plasmid, primarily within the antibiotic resistance genes (ampicillin resistance or tetracycline resistance) or outside the rop gene.

Therefore, the cloning site present in the rop site of E. coli cloning vector pBR322 is for Pvu II.