There are two types of DNA libraries that are constructed by genetic engineers using scientific methods. These can be classified as cDNA libraries as well as Genomic libraries. The major distinction in cDNA as well as Genomic library is the fact that cDNA library is a repository for the complementary DNA cloned from the all mRNA in an organism whereas genome DNA libraries includes the cloned fragments from the complete genome of an organism. It is bigger that those of the cDNA library.
What is a cDNA library?
- The cDNA library is an assortment of DNA complementary (cDNA) created from the total mRNA in an organism.
- The procedure for making a product involves several stages. The purification of mRNA total from an animal is the initial step.
- Isolated mRNA can be transformed into cDNA strands through the reverse transcription process.
- Reverse transcription is assisted by an enzyme known as reverse transcriptase. It employs a 3′ primer to initiate the synthesis of the initial CDNA strand which is complementary to the template mRNA.
- Double stranded cDNA that result is transformed into smaller fragments by restriction enzymes and then put into vectors that are suitable for the.
- The recombinant molecules that have been constructed are later incorporated to host cells and grown in a medium to generate Clones.
- The collection of clones that contain cDNA fragments from an organism is called an cDNA library.
- Fully cut mature mRNA does not contain regulatory and intron regions. So non-coding segments are not found in cDNA libraries like in the genomic library.
- Libraries of cDNA are essential to study the functions of genes, coding regions and expression of genes, etc.
What is a Genomic Library?
- A genomic DNA collection is an assortment of clones that contain the fragments of the total genomic DNA in an organism.
- It contains the whole genome of the organism, including both coding or noncoding genes.
- The creation of a genome library is done using Recombinant DNA technology and is followed by the process of cloning (genetic engineering). There are various steps in the creation of a library.
- The process begins with genomic DNA extraction. Utilizing the appropriate DNA extraction method The genomic DNA total of an organism needs to be extracted.
- The DNA is then reduced to manageable size or into specific fragments through restricting endonucleases (DNA cutting enzymes).
- Fragmented DNA must be introduced into vectors with DNA Ligases (DNA joiners).
- A vector is an organism that self-replicates. Plasmids and bacteriophages are the most commonly utilized vectors in the technology of recombinant DNA.
- These ligated vectors are referred to as recombinant DNA because they contain both their own and inserting DNA sequences. Recombinant vectors are inserted into the host bacterium, and then modified to take up the recombinant vectors within the bacteria’s cell.
- Bacteria that have recombinant vectors (plasmids) must be cultivated in a culture medium. As a result of the bacterial multiplication process, bacteria’s DNA, in conjunction with recombinant DNA plasmids replicate their genomes, and produce Clones.
- The clones comprise the complete genome of the organism from which they originated. This is why it is referred to as a genomic library.
- Plasmids can be easily separated from the chromosomal DNA in bacteria to create the genome library of the organism.
- If a specific organism is home to gene expressions that are of interest it is possible to find it in the genome library using hybridization with the molecular probe (markers).
- Genomic libraries are essential to understand the function and structure of genomics specific genes, gene loci genetic mapping and mutations, as well as the sequencing of genes, the finding of novel therapeutic genes, etc.
Difference between genomic and cdna library
|Genomic DNA library||cDNA library|
|Genomic library is a collection of the clones bearing the total genomic DNA of an organism.||cDNA library is a collection of the clones bearing the complementary DNA to the mRNA of an organism|
|Genomic library consists of the entire genomic DNA including noncoding (introns and regulatory) DNA.||cDNA library contains only the coding sequences; it does not contain introns.|
|Genomic library is large.||cDNA library is small.|
|The starting material is DNA.||Starting material is mRNA|
|Reverse transcription does not happen.||Reverse transcription happens in the first cDNA strand synthesis.|
|It include all possible fragments of DNA from a given cell or organism.||cDNA library carries only expressed gene sequences.|
|Vector used genomic library include plasmid, cosmid, lambda phage, BAC and YAC in order to accommodate large fragments||Vectors used cDNA library include plasmid, phagemids, lambda phage etc to accommodate small fragments as cDNA has no introns.|
|Restriction endonucleases and ligases are important for its construction.||Reverse transcriptase enzyme plays an important role in its construction.|
|They carry introns also.||They lack introns.|
|They may represent the DNA of both eukaryotic and prokaryotic organisms.||They represent the DNA of only eukaryotic organisms.|
|They are not capable of expression in prokaryotes (like the bacteria) because they carry introns and prokaryotes do not have machinery to process introns.||They are capable of expression in bacteria because they lack introns.|