Question

What are DNA libraries?

Answer 1

DNA library technology is based on molecular biology, genetic engineering and protein engineering. There are two types of DNA libraries based on the source of DNA used- Genomic library and cDNA library. In the genomic library genomic DNA of the organism is used whereas in cDNA library, complementary DNA is produced using mRNA of the organism. Preparation of the DNA library requires a cloning vector and a host organism.

Complete answer:
A DNA library is a collection of DNA fragments from an organism that were cloned in vectors for ease of purification, storage and analysis. These libraries help scientists to identify and isolate desired genes for genetic studies.
Two types of DNA libraries can be constructed- Genomic DNA library and cDNA library. A genomic library is a set of clones that represents the entire genome of a given organism. Here, DNA is extracted from the cell, digested, inserted into a cloning vector, transformed and then amplified. Genomic libraries are useful in determining the complete genome sequence of any organism. It can be used for the generation of transgenic animals through genetic engineering. It is also helpful in the study of genetic mutations in cancer tissues.
In cDNA library, mRNA is purified from a particular cell or tissue and it’s converted back to a DNA template by the use of an enzyme called reverse transcriptase. cDNA library represents the genes that were being actively transcribed in that particular source under the physiological and environmental conditions that existed when the mRNA was purified. These libraries are useful in reverse genetics, discovery of novel genes, in vitro study of gene function, study of mRNA expression etc.

Note:
There is another type of library called the synthetic mutant library. Here variations are created artificially in the gene sequence using techniques like error-prone PCR, DNA shuffling or transposon based indels to produce variants of the original gene. The expressed proteins are then screened for variants which exhibit favourable properties. cDNA library is useful in protein engineering and experimental evolution studies.