Genomic Library vs. cDNA Library
What is Genomic Library?
In gene cloning process, the gene of interest is copied out of DNA separated from an organism. When DNA is separated from an organism, its all genes are extracted at one time. DNA of organism contains thousands of different genes. Genetic engineer finds one specific gene which encodes the specific protein of interest. There is no one technique by which a specific gene from DNA can be found so Scientists make gene libraries to catalog the organism’s DNA. Scientists, then select the desired gene from the library. Gene library is a collection of living bacteria colonies that have been transformed with different pieces of DNA from the organism that is the source of the desired gene. DNA are extracted from organism to construct a library which is an organized form of DNA. Genomic library and cDNA are two types of gene libraries. Various techniques of gene cloning have been used as gene strategies in recombinant technology. DNA fragments are separated by cutting with specific restriction enzymes from parent DNA. These fragments are ligated into vector molecules, and the collected molecules are transferred into host cells, one molecule in each cell. The genomic library consists of introns, junk DNA, and many other fragments. In this library, DNA is broken into smaller fragments within a cell. After this, all the little parts are inserted into a vector to make a library. The genomic library contains all DNA of the entire cell and genes consists all of their introns. Genomic DNA is the translation of the whole genome. It does not code the entire part on one codon because of the size of introns. There is no splicing mechanism in a genomic library which causes difficulty in the expression of genes taken from this library.
What is cDNA Library?
cDNA library is constructed by selecting one cell or tissue type. Then mRNA is isolated from that cell or tissue. A DNA copy of mRNA molecule is made using specific enzyme reverse transcriptase enzyme. So cDNA library contains that particular DNA which is present in mRNA. No introns and no DNA sequence are present in this library. In this library, all clones are full-length. Moreover, a cDNA clone is necessary to transect cells for protein production or for cell-based assays.