Explain the roles of the following with the help of an example each in recombinant DNA technology:

(a) Restriction Enzymes

(b) Plasmids


(a) Restriction enzymes :

  1. Restriction enzymes belong to the class of enzymes nucleases which breaks nucleic acids by cleaving their phosphodiester bonds.
  2. Since Restriction endonucleases cut DNA at specific recognition site, they are used to cut the donor DNA to isolate the desired gene.
  3. The desired gene has sticky ends which can be easily ligated to cloning vector cut by same restriction enzymes having complementary sticky ends to form recombinant DNA
  4. An example is EcoR1 which is obtained from E.coli bacteria “R” strain which cuts DNA at specific palindromic Recognition site.
    5‘ GAATTC 3‘
    3‘ CTTAAG 5‘

(b) Plasmids :

  1. Plasmids are autonomous, extrachromosomal circular double-stranded DNA of bacteria
  2. Since they are small and self replicating,they are used as cloning vectors in genetic engineering.
  3. Some plasmids have antibiotic resistance genes which can be used as marker genes to identify recombinant plasmids from non-recombinant ones.
  4. The plasmids are cut and ligated with desired genes and transformed into a host cell for amplification to obtain the desired products.
  5. An example of artificially modified plasmids is pBR322 ( constructed by Bolivar and Rodriguez) or pUC (constructed at university at California).


Define recombinant DNA.

Recombinant DNA is the artificially created DNA which incorporates DNA segments from different sources into one.
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What is genetic engineering ?


Genetic engineering is a technique for artificially and deliberately modifying DNA (genes) to suit human needs. It is used to change the genetic makeup of the cells by using Recombinant DNA technology 
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Name the most commonly used bioreactor and describe its working.


The most commonly used bioreactors are of stirring type. A stirred - tank reactors is usually cylindrical or with a curved base to facilitate the mixing of the reactor contents. The stirrer facilitates even mixing and oxygen availability throughout the bioreactor. The bioreactor has an agitator system, an oxygen delivery system and a foam control system, a temperature control system. pH control system and sampling ports so that small volumes of the culture can be withdrawn periodically.


What is the role of restriction endonuclease ?

Restriction endonucleases are specific enzymes which can cleave double stranded DNA at specific sites called recognition sequences. Restriction endonucleases provide protection to the bacteria by restricting the growth of bacteriophages. They also serve as tools for Recombinant DNA technology.

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