stem, where it can cause a cancerous growth known as
a crown gall. The bacterium, which infects dicotyledonous
plants only, contains plasmid (known as a Ti plasmid)
that carries the genes for tumour formation. When the
bacterium invades the host cells, the Ti plasmid enters the
host nuclei. Part of the Ti plasmid become inserted into the
chromosome, where it produces copies of itself. For using Ti
plasmid as a vector, researchers have eliminated its tumour
causing properties while keeping its ability to transfer DNA
into plant cells. This bacterium is called natural genetic
engineer because genes carried by Ti plasmid produce effect
in several parts of the plant.
- (a) Proinsulin has A, B and C polypeptide strands. It is
non-functional. The mature insulin has only A and B
polypeptide strands and it is functional.
(b) From the human cell, DNA containing insulin gene is
isolated. The two DNA sequences corresponding to A
and B chains of human insulin is introduced into the
plasmids of E. coli to produce insulin chains A and B.
The extracted chains A and B are combined by creating
disulphide bonds to form human insulin (humulin).
(c) The insulin prepared by rDNA technology does not
produce sensitive allergic reactions and immunological
reactions. Those insulin used earlier, produced allergic
reactions and other complications to the foreign
protein as earlier insulin were extracted from pancreas
of slaughtered cattle and pigs.
- Competent host is essential for biotechnology experiment.
Since DNA is a hydrophilic molecule, it cannot pass through
membranes, so the bacterial cells must be made capable to
take up DNA i.e., made competent.
This can be achieved by :
(i) Treatment of DNA with divalent cation of CaCl 2 or
rubidium chloride. Treating them with a specific
concentration of a divalent cation, increases the
efficiency with which DNA enters the bacterium
through pores in its cell wall.
(ii) Heat shock treatment of DNA – Recombinant DNA
(rDNA) can be forced into cells by incubating the cells
with recombinant DNA on ice, followed by placing
them briefly at 42°C (heat shock) and then putting
them back on ice. This enables the bacteria to take up
the recombinant DNA.
- Different steps involved in RNA interference are as follows:
(i) Double stranded RNAs are processed into approximately
21-23 nucleotide RNAs with two nucleotides. An
RNase enzyme called dicer cuts the dsRNA molecules
(from a virus, transposon, or through transformation)
into small interfering RNAs (siRNAs).
(ii) Each siRNA complexes with ribonucleases (distinct
from dicer) to form an RNA-induced silencing complex
(RISC).
(iii) The siRNA unwinds and RISC is activated.
(iv) The activated RISC targets complementary mRNA
molecules. The siRNA strands act as guides where the
RISCs cut the transcripts in an area where the siRNA
binds to the mRNA. This destroys the mRNA.
(v) When mRNA of the parasite is destroyed no protein is
synthesised. It results in the death of the parasite in the
transgenic host.
- (a) Benefits derived from transgenic animals are as follows:
(i) They produce useful biological products, that can be
created by introduction of portion of gene, which
codes for a particular product such as human protein
(a - 1- antitrypsin) from transgenic sheep is used to
treat emphysema.
(ii) Transgenic mice are being developed for use in testing
the safety of vaccine before they are used in humans.
(iii) They carry genes which make them more sensitive to
toxic substances than non-transgenic animals. They are
then exposed to toxic substances and the effects are
studied.
(b) The ethical issues concerned with the production of
transgenic animals include:
(i) Introduction of a transgene from one species into
another species violates the ‘integrity of species’.
(ii) Transfer of human genes into animals (and vice-versa)
dilutes the concept of ‘humanness’.
(iii) When animals are used for production of
pharmaceutical proteins, they are virtually reduced to
the status of a ‘factory’.
(iv) Use of animals in biotechnology causes great suffering
to them.
(v) It is disrespectful to living beings, and only exploits
them for the benefit of human beings.
(c) Neeraj shows ethical values as he is kind and concerned
about the animals while Mohit shows values towards
the betterment of human race. Both of them are
knowledgeable and have scientific aptitude.
- The cloning vectors are DNA molecules that can carry a
foreign DNA segment and replicate inside the host cell.
These are plasmids, bacteriophages, cosmids, phagemids,
yeast artificial chromosome (YAC), bacterial artificial
chromosome (BAC), transposons and virus.
Cloning vector carry rDNA and they generally have high
copy number, they can produce multiple numbers of
required gene. Vectors help in easy linking of foreign DNA
and in selection of recombinants from non-recombinants.
The entire procedure of gene cloning or recombinant DNA
technology may be classified into the following six steps for
the convenience in description and on the basis of the chief
activity performed.
(i) Production and isolation of the DNA fragments to be
cloned.
