Biotechnology—Principles and Processes — BIOLOGY STD 12 Science — Question

A vector is a DNA molecule which is used for transporting exogenous DNA into the host cell. A vector is capable of self-replication and stable integration inside the host cell.
The molecular analysis of DNA has been made possible only after the discovery of vectors. The whole process of molecular cloning involves the following steps :
(1) Digestion of DNA fragments of the target segment and the vector DNA with the help of restriction enzymes.
(2) Ligation of the target segment with the vector DNA with the help of DNA ligases, and
(3) Introduction of the ligated segment into the host cell for propagation.
General characteristics of a vector :

• It should have an Origin of Replication, known as 'ori', so that the vector is capable of autonomous replication inside the host organism.
• It must possess a compatible restriction site for insertion of DNA molecule.
• A vector should always harbour a selectable marker to screen the recombinant organism. This selectable marker can be an antibiotic resistance gene.
• For easy incorporation into the host machinery, a vector should itself be small in size and be able to integrate size of the insert.

A cloning vector is also a fragment of DNA which is capable of self-replication and stable maintenance inside the host organism. It can be extracted from a virus, plasmid or cells of a higher organism. Most of the cloning vectors are genetically engineered. It is selected based upon the size and the kind of DNA segment to be cloned.
The cloning vectors must possess the following general characteristics :

• It should small in size.
• It must have an origin of replication.
• It must also be compatible with the host organism.
• It must prossess a restriction site.
• The introduction of donor fragment must not intervene with the self-replicating property of the cloning vector.
• A selectable marker, possibly an antibiotic resistance gene, must be present to screen the recombinant cells.
• It should be capable of working under the prokaryotic as well as the eukaryotic system.
• Multiple cloning sites should be present.

Importance of Cloning Vectors : Cloning Vectors are used as the vehicle for transporting genetic material into another cell. This foreign segment of DNA is replicated and expressed using the machinery of the host organism.
A cloning vector facilitates amplification of a single copy DNA molecule into many copies. Molecular gene cloning is difficult without the use of the cloning vectors.