A: Restriction enzymes:
Restriction enzymes are known to restrict growth of bacteriophages in bacteria.
Nearly 900 restriction enzymes are isolated from bacteria.
Each restriction enzyme recognises a different recognition sequence on DNA.
Restriction enzymes belong to the enzyme sub-class nucleases.
They are of two types:
Exonucleases and Endonucleases.
Exonucleases remove nucleotides from the ends of the DNA.
Endonucleases make cuts at specific positions within DNA.
For Example EcoRI is a restriction enzyme that recognises a
palindromic sequence on DNA and cuts between G and A.
Restriction enzyme cause staggered cuts and create sticky ends in DNA.
These enzymes are used in genetic engineering to form recombinant DNA molecules.
Q: What are different methods of insertion of recombinant DNA into the
host cell?
A: The recombinant DNA may be inserted into the host cell by any of
the following methods:
Heat shock: The host cells are incubated with rDNA on ice followed by
a heat shock at 42° temperature and putting them back on
ice. This enables the bacteria to take up rDNA.
Micro injection: In animals recombinant DNA is directly injected into
the nucleus using micro-injection.
Biolistic or gene gun method: This method is used for plant cells. The
host cells are bombarded with high velocity micro particles of gold or
tungsten coated with DNA.
Disarmed pathogen: In this method disarmed pathogen vectors are
allowed to infect the host cell to transfer the rDNA into the host.
Q: List out the beneficial aspects of transgenic plants.
A: Plants with desirable characters created through gene transfer
methods are called transgenic plants. Ti plasmid from Agrobacterium
tumifaciens is used as vector to transfer genes in plants. Some of the
beneficial aspects of transgenic plants are:
Transgenic plants are resistant to pathogens and pests.
Ex: Transgenic papaya (resistant to ring spot virus),
Transgenic tomato (resistant to bacterium Pseudomonas) and Transgenic
potato resistant to the fungus Phytophthora).
They are made suitable for food processing by developing an
impermeable fruit wall and bruise resistance for long storage and
higher shelf life. Ex: Flavr Savr tomato
Some transgenic plants have improved nutritional value. Ex: Golden
rice from Taipei enriched with vitamin A.
They may be made male sterile so as to reduce the cost of emasculation
and hybrid seed production. Ex: Brassica napus
Some of them are tolerant to abiotic stresses caused by cold, drought,
salt and heat.
Ex: Basmati rice, Roundup ready soyabean.
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