(i) Describe the characteristics that a cloning vector must process.
(ii) Why DNA cannot pass through the cell membrane ? Explaine. How is a bacterial cell made competent to take up recombinate DNA from the medium?
(i) 1. Vectors are used to deliver an alien piece of DNA into a suitable host which is called cloning vector or gene carrier. The desired gene is introduced into a vector wherein recombinate DNA is formed.
Example: Plasmids and Bacteriophage vectors
2. If alien piece of DNA is linked with Bacteriophage or plasmid DNA we, can multiply its number of the plasmid or Bacteriophage.
3. They also help in selection of recombinants from non-recombinants.
(ii) 1. DNA is a hydrophilic molecule. It cannot pass through cell memberances. In order to force bacterial cells must be first made 'competent'. This is done by treating them with a speciefic concentration of a divalent cation of calcium. This increases the effciency with which DNA enters the cell through the pores in its cell wall. rDNA can then be forced into such cells by incubating the cells with rDNA on ice followed by placing them thatC (heart shock) and them putting back on ice. This enables the bacteria to take up to rDNA.
2. Microinjection: rDNA is directly injected into the nucleus of an animal cell.
3. Biolistics or Gene gun : It is suitable for plants. Cells are bombarded with high velocity micro particles of gold or tungsten coated with DNA.
4. Disarmed pathogen vectors like Agrobacterium tumifacience which when allowed to infect the cell transfer the rDNA in to the host.