Q1. Source: ICMR JRF 2020
Microinjection is a method used to:
a. Produce sticky ends of DNA
b. Provide protection against pathogens
c. Purify the DNA
d. Inject recombinant DNA into the nucleus of an animal cell
Microinjection is a technique in which a very fine glass micropipette is used to directly introduce substances such as recombinant DNA, RNA, proteins, or CRISPR components into individual cells. It is commonly used to deliver recombinant DNA into the nucleus of animal cells, particularly fertilized eggs or embryos, for the production of transgenic animals.
Statement Analysis
A. Produce sticky ends of DNA: Incorrect. Sticky ends are generated by restriction endonucleases, not by microinjection.
B. Provide protection against pathogens : Incorrect. Protection against pathogens is achieved through the immune system or vaccination, not by microinjection itself.
C. Purify the DNA : Incorrect. DNA purification is carried out using extraction and purification techniques such as column-based or phenol-chloroform methods.
Correct answer: d. Inject recombinant DNA into the nucleus of an animal cell
Q2. Source: CSIR NET NOV 20; Session I
In a cloning experiment, a DNA molecule isolated as a PstI fragment was inserted into the PstI site of a cloning vector that is 3 kb in length. Digestion of the confirmed clones with PstI resulted in the appearance of a single band corresponding to 3 kb in an agarose gel. Based on this information, what is the probable size of the cloned fragment?
a. 6 kb
b. 1.5 kb
c. 3 kb
d. 4.5 kb
The cloning vector is 3 kb long and contains a single PstI restriction site. The DNA insert was also generated using PstI, so after ligation, the recombinant plasmid contains two PstI sites flanking the insert.
When the recombinant plasmid is digested with PstI, it is expected to produce two DNA fragments:
- the vector (3 kb), and
- the insert.
However, the agarose gel shows only one band at 3 kb. This can occur only if both fragments are exactly the same size (3 kb). DNA fragments of identical length migrate together during electrophoresis and appear as a single, brighter band.
Therefore, the cloned DNA fragment must also be 3 kb in size.
Correct Answer: c. 3 kb
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