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Genomic library and CDNA library are used in gene cloning to isolate different DNAs. The key difference between these two libraries is that genomic library contains DNA fragments that express the whole genome of an organism while in cDNA library, mRNA is taken from specific cells of an organism, and then cDNA is made from that mRNA in a reaction which is catalyzed by an enzyme.
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.
Genomic Library vs. cDNA Library
- The genomic library has been composed directly of the genomic DNA.
- cDNA Library has been formed by using mRNA as a template.
- Genomic library expresses entire genome of the organism.
- cDNA library represents only genes of specific conditions.
- Two enzymes, restriction endonucleases, and ligases are significant for genomic library construction.
- Reverse transcriptase enzyme plays a major role in cDNA library construction.
- Genomic library expresses the DNA of both prokaryotic and eukaryotic organisms.
- cDNA library represents the DNA of only eukaryotic organisms.
- A genomic library is not capable of expression in the prokaryotic organism because they possess introns and the prokaryotic organism has no machinery to process introns.
- cDNA library is capable of genome expression in bacteria which is prokaryotic because they lack introns.