DNA LIBRARY (Part 1)

 DNA Library ( Gene library )

What is DNA library ....?

The collection of the clone DNA fragments that represent the entire genome of a species is referred as gene library .

- Gene library is a collection of different DNA sequences from an organism where each sequences has been cloned into suitable vector .

Type of gene library :- 

Depending upon the availability of source DNA gene library is of two type 

1) genomic library 

2) cDNA library 

1) Genomic Libraries :- 

It is a collection of all clone of DNA fragment that represent the complete genome of an organism .

Construction of genomic library :-

For construction of genomic library, the requirements are :- 

1) Isolated genomic DNA 

2) Restriction enzyme 

3) Plasmid ( vector DNA )

                Fig. 1 ( step of genomic libraries) 

Procedure of construction of genomic library :- 

- Genomic libraries have the potential to contain a clone of every gene found in the cells of any organism. 

- This is because the starting material in a genomic library is the DNA extracted from the cells of the organism of interest. 

The steps performed to make a genomic library are listed below.

1) Isolate a sample of DNA from the organisms cells

2) Cut the DNA into “gene-size” pieces with a restriction enzyme or enzymes.

3) Cut a cloning plasmid with the same restriction enzymes.

4) Add the cut plasmid and genomic DNA to the same test tube and add DNA ligase. This will make a collection of recombinant and non recombinant plasmids.

5) Transform the collection of plasmids into a laboratory strain of E. coli that is susceptible to antibiotics.

6) Plate the bacteria on Amp/X-gal plates. Incubate at body temperature overnight.

7) Observe the plates, select white colonies and transfer to new Amp plates.

8) Make a large collection of white colonies to form the genomic library.

Once a library is made it can be a resource used to isolate colonies that contain any gene of the organism. 

Advantages of genomic library :-

- It is easy to construct and screen .

- It contain DNA fragments of entire genome .

- All the cloned DNA are in stable form .