7.013 Recitation 10

of Lectures 15 & 16: Library: A genomic library is a population of host bacteria, each of which carries a DNA molecule that was inserted into a cloning vector, such that the collection of cloned DNA molecules represents the entire genome of the source organism. The DNA molecules of an organism of interest are isolated, partially digested by an endonuclease restriction enzyme and ligated into vectors. The vectors can then be taken up by suitable hosts. The hosts are kept in liquid media and can be frozen at -80°C for a long period of time. Usually the hosts are bacteria that do not contain any plasmids, so as to be sensitive to antibiotics.A cDNA library is a collection of cloned complementary DNA (cDNA) fragments inserted into a collection of host cells. A cDNA is produced from fully transcribed mRNA found in the nucleus and therefore contains only the expressed genes of an organism. In eukaryotic cells the mature mRNA is already spliced, hence the cDNA produced lacks introns and can be readily expressed in a bacterial cell. While information in cDNA libraries is a powerful and useful tool since gene products are easily identified, the libraries lack information about introns, and other regulatory elements found in a genomic DNA library.