Restriction endonucleases have played a very significant role in rDNA technology. Explain the roles of EcoRI and DNA ligase in formation of recombinant DNA.

Hershey and Chase carried out their experiment under three steps: (a) Infection, (b) Blending, and (c) Centrifugation. Explain each one of these steps that helped them to prove that DNA is the hereditary material.

OR

(a) Why does DNA replication occur within a replication fork and not in its entire length simultaneously?

(b) ‘‘DNA replication is continuous and discontinuous on the two strands within the replication fork.’’ Give reasons.

(a) What is the breeding of crops for enhancing their nutritional value called? Why is the need felt for enhancing the nutritional value of the crops?

(b) Rice, wheat and maize are the most commonly used food grains the world over. How have these grains improved in their nutritional value in comparison to their conventional varieties?

OR

(a) Write the scientific names of the source plants from where opioids and canabinoids are extracted.

(b) Write their receptor sites in the human body. How do these drugs affect the human beings?

Why DNA cannot pass through the cell membrane? How can the bacteria be made competent to take up a plasmid? Explain a method for introduction of alien DNA into a plant host cell. Name a pathogen that is used as a disarmed vector.

Study the figure of vector pBR322 given below.

Identify A, B and C and explain their roles in cloning a vector.

OR

Many people are apprehensive of accepting GM crops. Give three reasons so as to convince them to use these crops.