The genomic library and the CDNA library are used in gene cloning to isolate different DNAs. The key difference between these two libraries is that the genomic library contains DNA fragments that express the entire genome of an organism, whereas in the cDNA library, the mRNA is taken from specific cells of an organism and then the cDNA is made to starting from that mRNA in a reaction catalyzed by an enzyme.
|Genomic library||CDNA library|
|Definition||A genomic library is a collection of the total genomic DNA of a single organism. DNA is stored in a population of similar vectors, each of which contains a different DNA insert.||A CDNA library is a combination of cloned CDNA fragments inserted into a collection of host cells, which together form a part of the organism’s transcriptome.|
|Expression||Complete genome||Only specific genes.|
|Vector||It uses plasmids, cosmids, lambda phage, YAC and BAC for the accommodation of large fragments.||It has no introns, so it uses plasmids, phagemids, lambda phages to accommodate small fragments.|
What is the genomic library?
In the process of gene cloning, the gene of interest is copied from the separate DNA of an organism. When DNA is separated from an organism, all of its genes are extracted at the same time. The body’s DNA contains thousands of different genes. The genetic engineer finds a specific gene that codes for the specific protein of interest. There is no single technique by which a specific gene can be found in DNA, so scientists create gene libraries to catalog the organism’s DNA. Scientists then select the desired gene from the library. The gene library is a collection of colonies of living bacteria that have been transformed with different pieces of DNA from the organism that is the source of the desired gene. DNA is extracted from the body to build a library that is an organized form of DNA. The genomic library and the cDNA are two types of gene libraries. Various gene cloning techniques have been used as gene strategies in recombinant technology. The DNA fragments are separated by cutting them with specific restriction enzymes from the original DNA. These fragments are ligated into vector molecules and the collected molecules are transferred to host cells, one molecule in each cell. The genomic library consists of introns, junk DNA, and many other fragments. In this library, DNA is divided into smaller fragments within a cell. After this, all the small parts are inserted into a vector to make a library. The genomic library contains all the DNA of the whole cell and genes consist of all its introns. Genomic DNA is the translation of the entire genome.
The cDNA library is constructed by selecting a tissue or cell type. The mRNA is then isolated from that cell or tissue. A DNA copy of the mRNA molecule is made using enzyme-specific reverse transcriptase enzyme. So the cDNA library contains that particular DNA that is present in the mRNA. There are no introns or DNA sequences in this library. In this library, all clones are complete. Furthermore, a cDNA clone is necessary to section cells for protein production or for cell-based assays.
Genomic library vs. cDNA library
- The genomic library has been composed directly from genomic DNA.
- The cDNA library has been formed using mRNA as a template.
- The genomic library expresses the entire genome of the organism.
- The cDNA library represents only genes for specific conditions.
- Two enzymes, restriction endonucleases and ligases, are important for the construction of genomic libraries.
- The reverse transcriptase enzyme plays an important role in the construction of the cDNA library.
- The genomic library expresses the DNA of prokaryotic and eukaryotic organisms.
- The cDNA library represents the DNA of only eukaryotic organisms.
- A genomic library is not capable of being expressed in the prokaryotic organism because it has introns and the prokaryotic organism does not have machinery to process introns.
- The cDNA library is capable of expressing the genome in bacteria that are prokaryotic because they lack introns.