Which of the following restriction enzymes produces blunt ends? [2016]
SalI
EcoRV
XhoI
Hind III
EcoRV is a type II restriction endonuclease isolated from certain strains of E. coli. It creates blunt ends. It recognises the palindromic sequence of 6 bases. SalI, XhoI and Hind III restriction enzymes produce sticky ends.
Which of the following is not a feature of the plasmids? [2016]
Transferable
Single-stranded
Independent replication
Circular structure
Plasmids are extra-chromosomal, self-replicating, usually circular, double-stranded DNA molecules that serve as vectors which carry foreign DNA segment and replicate inside host cell.
Which of the following is a restriction endonuclease? [2016]
DNase I
RNase
Hind II
Protease
Hind II is the first restriction endonuclease. It was isolated from Haemophilus influenzae Rd. It always cuts DNA at specific position producing blunt ends. DNase I is an endonuclease that cleaves DNA preferentially at phosphodiester linkages adjacent to a pyrimidine nucleotide. RNase is a type of nuclease that catalyses the degradation of RNA into smaller components. It can be endoribonuclease or exoribonuclease. A protease is an enzyme that performs proteolysis, i.e., protein catabolism by hydrolysis of the peptide bonds.
The introduction of T-DNA into plants involves [2015]
exposing the plants to cold for a brief period
allowing the plant roots to stand in water
infection of the plant by Agrobacterium tumefaciens
altering the pH of the soil, then heat-shocking the plants.
Ti plasmid (tumor inducing) from the soil bacterium Agrobacterium tumefaciens is effectively used as vector for gene transfer to plant cells. The part of Ti plasmid transferred into plant cell DNA, is called the T-DNA. This T-DNA with desired DNA spliced into it, is inserted into the chromosomes of the host plant where it produces copies of itself. Such plant cells are then cultured, induced to multiply and differentiate to form plantlets. By transferring into soil, the plantlets grow into mature plants, carrying the foreign gene, expressed throughout the new plant.
Which vector can clone only a small fragment of DNA? [2014]
Bacterial artificial chromosome
Yeast artificial chromosome
Plasmid
Cosmid
Plasmids have been modified to be used as vectors. They can clone DNA fragments of about 10 kbp size while cosmid can carry upto 45 kbp, YAC can carry upto 1000–2500 kbp and BAC can carry around 300–350 Kbp long DNA fragments.
Commonly used vectors for human genome sequencing are [2014]
T - DNA
BAC and YAC
expression vectors
T/A cloning vectors
Bacterial artificial chromosome (BAC) vectors are based on natural, extra-chromosomal plasmid of E. coli. BAC vector contains genes for replication and maintenance of the F-factor, a selectable marker and cloning site. These vectors can accommodate upto 300–350 kb of foreign DNA and are also being used in genome sequencing project. Yeast artificial chromosome (YAC) vectors are used to clone DNA fragments of more than 1Mb in size. Therefore, they have been exploited extensively in mapping the large genomes, e.g., in the Human Genome Project. These vectors contain the telomeric sequence, the centromere and the autonomously replicating sequence from yeast chromosomes.
