1. Compare and contrast the use of plasmids and bacteriophage vectors in gene cloning. Your answer should include diagrams of named vectors, a description of standard protocols for their usage and an...

Running head MOLECULAR GENETICS: STRUCTURAL AND FUNCTIONAL APPROACHES
Molecular Genetics: Structural and Functional Approaches
Name:
Professor:
Course:
Date:
2
Molecular Genetics: Structural and Functional Approaches
1. Vectors: Introduction and Key characteristics
Vector means; carrier molecule which can be used for transfer of a moiety (for instance,
gene) from one place to another as; from one organism to another creature. There could be
observed various vectors such as; Plasmids and Bacteriophages which are termed as;
considerably valuable tools by Molecular biologists (Hao et al., 2002).
Plasmid
Plasmid may be defined as; a comparatively small, double-stranded, closed-circular DNA
molecule which can be found in the host organism as an extra-chromosomal moiety. These are
quite popular vectors among Genetic engineers because of their specific features such as; (i)
small size (thus; easy to handle), (ii) presence of origin of replication (that can assist in
replication of plasmid as well as DNA fragment inserted in it) and marker (ease the selection
procedure) in it, and (iv) its appreciable ability to produce several copies of the inserted molecule
etc (Roberts et al., 2003).
Application method
How plasmid is used by scientists for the purpose of expression of novel characteristics in
prokaryotic and eukaryotic cells it can be understood as follows:
1. Isolation of plasmid from E.coli.
2. Application of Restriction Endonuclease (R.E) enzyme to cut the plasmid at a particular
site.
3. Isolation of gene from donor, and its insertion into plasmid.
4. Application of Ligase to seal the plasmid.
5. Introduction of plasmid into host cell (as; E.coli) through cell transformation technology
(for example, electroporation) and,
3
Molecular Genetics: Structural and Functional Approaches
6. Production of several copies of thus introduced gene (Chen et al., 1995).
Amp
R
(Ampicillin Resistance marker sequence)
Tet
R

(Tetracycline Resistance
marker sequence) pBR322
Ori
(Origin of replication) Insertion of foreign sequence
via application
of R.E and Ligase
Recombinant Plasmid
Inserted DNA
Introduction into host cell (as; E.coli)
Transformed host cell
Cloned fragments of inserted DNA
4
Molecular Genetics: Structural and Functional Approaches
Bacteriophage Vectors
Besides plasmids, bacteriophages are also applied as cloning vectors in a universal
manner. Phage consists of a DNA molecule which might be cut via R.E for the purpose of
insertion of a foreign gene and thus produced chimeric phage particle might be sealed further
with the help of ligase enzyme. When such recombinant phage attacks on bacterium then
because of production of its multiple copies, gene inserted in original phage also gets amplified
which might be isolated and purified after a lytic cycle (Roberts et al., 2003).
Applications
Though, bacteriophages are popular cloning vectors, but their application as vector
restricts the size of foreign DNA that could be cloned due to the limited capacity of phage- head
to accommodate such particles. To conquer this trouble, such DNA segments might be
eliminated from phage that do not contain vital genes (Lander & Botstein, 1986).
Lambda Phage Genome (49 kb)
Replaceable region
DNA Recombination
Target DNA
Packaged Assembly
Host cell (as; E.coli)
Multiple copies of phage particle (Lytic cycle)
5
Molecular Genetics: Structural and Functional...