Cloning Vector - Plasmid & Bacteriophages

Recombinant DNA technology is a procedure that aims to change the phenotype of a creature (host). This is achieved by introducing and integrating genetically altered vector into the genome of the creature. Inserting the desired gene into the genome of the host is not as easy as it sounds. Fundamentally this process includes the initiation of a foreign piece of DNA into the genome containing the gene of our interest.  A cloning vector is crucial for this genetic engineering.

Cloning Vector

A recombinant DNA is formed by the desired gene which is integrated and carried by the help of a cloning vector. The host organism receives the desired genes from cloning vector as they are the essential segment of the tools concerning recombinant DNA technology and act as the ultimate vehicle. Due to having a high copy number, in recombinant DNA technology bacteriophages and plasmids are very commonly used as vectors.

Cloning of a vector is achieved with the help of the following features.

  • Origin of replication (Ori): The vectors are made up of an origin of replication. The replication begins from this sequence of nucleotide. In addition, it controls the number of DNA to be copied.

Cloning vector

  • Selectable marker: Insertion of the gene of interest, for example, genes encoding resistance to antibiotics, into host organism is called as transformation and such organisms are called transformants. The selectable marker in a vector sorts out the transformants from a non-transformants and allows the growth of the transformants. The normal E. coli cells do not carry genes which show resistance to antibiotics while a recombinant one show resistance to certain antibiotics like ampicillin. These genes act as a selectable marker in E.coli.
  • Site Cloner: Also known as recognition site. It is the site recognized by the restriction enzymes where the desired DNA’s are inserted. Multiple recognition sites may complex the process of cloning. The restriction enzymes split vectors at their recognition site to get the complementary sticky notes. Then the foreign DNA is ligated at this site.

Vectors for Gene Cloning

The vectors used for cloning can be a bacteriophage or plasmid of few bacteria which can trigger various diseases in both plants and animals. These pathogenic genes of the organism are altered and their pathogenicity could be inactivated.  This is used for delivering a gene of interest to the host without damaging the host cell. For example, a plasmid of Agrobacterium tumefaciens; it could induce tumour in plants which are modified to deliver recombinant DNA to the host plants.

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Practise This Question

Transcribed regions present in mature mRNA arise from ---(i)-- and transcribed regions not present in mature  mRNA arise from  ----ii----.