In genetics, a library is a collection of DNA fragments that have been propagated from a population of different species or organisms by scientists by the process of molecular cloning. Hence in molecular biology, there are many different types of DNA libraries. The two main types of libraries are cDNA, and genomic libraries. The application of the libraries depends on the DNA of original species before molecular cloning even though DNA library technology is the mainstay of current molecular biology.
In addition, there are many different types of cloning techniques utilized to propagate DNA. The most common way is to insert a piece of DNA fragment into a cloning vector and combine it with a recombinant DNA before placing it into a bacteria or yeast culture. From there scientists observe how the culture grows and analyze the amount of DNA molecules are propagated or cloned.
cDNA library is a combination of cloned cDNA fragments packed into a collection of host cells. cDNA is produced by transcribed mRNA that has been fully complete. Because it has been produced by mRNA, it only contains expressed genes of organism that the mRNA has copied. This often leads to possible mutation attack because the cDNA houses the expressed genes and if anything changes, the cDNA library can confirm the change and induce a mutation or viral infection. Usually cDNA library are used for eukaryotic genomes to reduce the amount of non-coding regions. Also they are used in prokaryotes to express any possible eukaryotic genes. cDNA is only powerful when reverse genetics is used because there isn’t a lot od genomic information that needs to be encoded.
To go through cDNA, it has to go through mRNA extraction and cDNA construction. To get mRNA, RNA has to be purified from the rest of the unwanted RNA in the strands. A way to do this is by using nucleotide coated resins where the poly-A tail binds to one of the RNA and cleaves the rest of the RNAs. After the mRNA is eluted by buffering and heat to melt the coating away and have the mRNA be isolated. cDNA construction is a continuation of the mRNA extraction. In this process the mRNA is tagged with a primer which allows the poly-A tail to be attached still. Then RNAse is released which removes the mRNA and leaves a single cDNA. The cDNA is then converted into a double stranded DNA by DNA polymerase and an OH binder. The last step is the action of ligase which cleaves and clones DNA sequences into bacterial plasmids. These plasmids are then selected and grown to be observed in cDNA.
A genomic library is a set of clones that are clustered together and represent the entire genome of the organism. The way the genomic library is set up is that they determine by the size of the genome and the toleration of the cloning system. The most common usage of genomic DNA is for tissues because the human body contains essentially the same DNA pieces. Some application of the genomic library includes determining the complete genomic sequences of an organism, source of genomic sequence for generations by genetic engineering, and how cancer arise from genetic mutation.
Since both libraries have their advantages and flaws, it is safe to say that both different types of libraries are reliable. In addition, with improving technologies, the DNA libraries will be much easier to use so that research for cancer and finding where in the cDNA is there a problem is easier. Not only we are able gain information about the genomes and DNA fragments, we can store the information in the libraries for future use.