Molecular Genetics Community Medicine


#1

Q-21. Two transgenic plants are genetically engineered using recombinant DNA technology. One plant was transformed using a plasmid vector with Green Fluorescent Protein gene and other plant was transformed with fire fly luciferase gene. Which plant will glow in the dark?
a) Both plants will glow
b) Neither will glow
c) Plant expressing green fluorescent protein will glow
d) Plant expressing fire fly luciferase will glow

Answer: Plant expressing fire fly luciferase will glow
Explanation:
Bioluminescence is defined as the ability of living organisms to emit light through the chemiluminescence phenomenon.
The light emission is due to transfer of electrons from a substrate, in presence of an enzyme called Luciferase. The electrons are transferred to a lower energetic level, with an output of energy in the form of light radiation.
Among the animals, it can be found insects, shellfishes and molluscan.
Green Fluorescent Protein is a protein produced by a jellyfish Aequorea victoria; which produces glowing points of light around the margin of its umbrella.
The light arises from photogenic cells. These cells generate light by a process of bioluminescence, whose components include a calcium-activated photo-protein (Aequorin) that emits blue-green light and an accessory green fluorescent protein, which accepts energy from aequorin and re-emits it as green light. Green fluorescent protein will not glow in dark in absence of Aequorin.
Important points:
A few years back the bioluminescence phenomenon found application in the healthcare field, in particular in the fight against cancer.
The Bioluminescent activated destruction technique consists in the transformation of tumorigenic cells so that they express both the photo-sensibilizing and the luciferase gene from the firefly.
This way the cells, emitting bioluminescence, commit some sort of suicide because the photo-sensibilizing reacts to the luminescence producing toxins.

Q-22. Cell fusion is an innovative method of preparing specific antibody technique to induce cell fusion includes following all except?
a) Attaching inactive viral particle on cell membrane
b) Adding ethylene glycol
c) Applying a small electric current
d) Reducing the viscosity of the membrane

Answer: Reducing the viscosity of the membrane
Explanation:
During the fusion process, B cells are isolated from the mouse spleen previously injected with an antigen, mixed with the mouse myeloma cell line and fusion is induced with polyethylene glycol (PEG).
The resulting hybridomas are then cultured in tissue culture medium containing hypo-xanthine, aminopterin, and thymidine (HAT).
Hybridoma multiplies and myeloma and B cells die.
Important point:
Hybridomas provide long term sources of highly useful monoclonal (Mono-specific) antibodies.

Q-23. What factor is responsible for deciding whether an antibody will remain membrane bound, or get secreted?
a) Carbohydrate content
b) Class switching
c) Differential RNA splicing
d) Surface charge

Answer: Differential RNA splicing
Explanation:
Differential RNA processing explains the progression from membrane-bound to secreted antibody.
Production of two forms of immuno-globins occurs by differential transcription of the germline C region of each heavy chain.
Membrane bound immuno-globin is identical to secreted immuno-globin except for an extra stretch of amino acids at C terminus of each heavy chain.
Their additional amino acids transverse the cell membrane and anchor the molecule in lipid bilayer.

Q-24. All of the following statements about lambda phage are true Except
a) In Lysogenic Phase, it fuses with host chromosome and remains dormant
b) In Lytic Phase it fuses with host chromosome and replicates
c) Both Lytic and Lysogenic Phases occur together
d) In Lytic Phase it causes cell lysis and releases virus particles

Answer: Both Lytic and Lysogenic Phases occur together
Explanation:
Lambda Bacteriophage:
In Lysogenic Phase, it fuses with host chromosome and remains dormant
In Lytic Phase it fuses with host chromosome and replicates
In Lytic Phase it causes cell lysis and releases virus particles
Important point:
Both Lytic and Lysogenic Phases do not occur to gather.

Q-25. The following methods can be used to detect the point mutation in the beta-globin gene that causes sickle cell anemia except?
a) Polymerase chain reaction with allele-specific oligo-nucleotide hybridization
b) Southern blot analysis
c) DNA sequencing
d) Northern blot analysis

Answer: Northern blot analysis
Explanation:
To detect the point mutation in the beta-globin gene that causes sickle cell anemia require DNA analysis.
Northern blot analysis is used to study the RNA.

Q-26. To synthesize insulin on a large scale basis, the most suitable starting material obtained from the beta cells of the pancreas is: (AIIMS Nov 2005)
a) Genomic DNA
b) Total cellular RNA
c) c-DNA of insulin
d) m-RNA of insulin

Answer: m-RNA of insulin
Explanation:
Insulin is synthesized on a large scale basis from complementary DNA (c-DNA), but this is not the starting material because these c-DNAs are derived from mRNAs with the help of Reverse transcriptase and DNA polymerase 1.
The c-DNA produced by this method is inserted into an appropriate cloning vector which produces a large number of c-DNA clones.

Q-27. Blue-White screening is used in molecular cloning for: (AIIMS May 2008)
a) To identify desired chromosomal DNA insert in plasmid vectors
b) To detect host DNA in situ
c) To detect gene mutation
d) To screen for recombinant vectors

Answer: To identify desired chromosomal DNA insert in plasmid vectors
Explanation:
The blue-white screen is a screening technique that allows for the rapid and convenient detection of recombinant bacteria in vector-based molecular cloning.
DNA of interest is ligated into a vector. The vector is then inserted into a competent host cell (bacteria), viable for transformation, which are then grown in the presence of X-gal. Cells transformed with vectors containing recombinant DNA will produce white colonies; cells transformed with non-recombinant plasmids (i.e. only the vector) grow into blue colonies.

Q-28. In karyotyping chromosomes are visualized through light microscope with resolution of
a) 5 kb
b) 500 Kb
c) 5 Mb
d) 50 Mb

Answer: 5 Mb
Explanation:
Karyotype analysis is a technique where chromosomes are visualized under a microscope.
The chromosomes are stained with certain dyes that show a pattern of light and dark bands (called the banding pattern). These bands reflect regional differences in the amounts of A and T versus G and C.
The banding pattern for each chromosome is specific and consistent allowing identification of each of the 24 chromosomes.
Karyotype analysis can detect large chromosomal abnormalities such as loss or gain of an entire chromosome or portions of a chromosome.
The chromosomes are stained with a dye (Geimsa), resulting in a banding pattern of light and dark stripes, known as G-banding. The patterns are specific, allowing us to identify each chromosome.
Important point:
Karyotype analysis detects both numerical and structural chromosomal aberration with overall resolution of 5 Mb and breakpoint resolution of 5-15 Mb.