CDNA LIBRARY

A 'cDNA library' is a collection of clones containing cDNAs. cDNA libraries are often intended to represent as many as possible of the mRNAs contained within a cell. Because working with mRNA is difficult (as mRNA is unstable and is easily degraded by RNases which can be found even on the skin), researchers use an enzyme called ''reverse transcriptase'' which will produce a DNA copy of each mRNA strand. Referred to as cDNA these reverse transcribed mRNAs are collectively known as the library.
Such a library has several uses. A cDNA of an eukaryotic organism (for example, a human) can be cloned into a prokaryotic organism (for example, ''E. coli'') and ''expressed'' (translated into the appropriate protein) there (with limitations, for example posttranslational modification). A cDNA library is also important for analysis through bioinformatics. The complete cDNA library of an organism gives the total of the proteins it can possibly express. Also, comparison of cDNA sequence between libraries constructed from cells derived from different organisms can provide insight into the genetic and evolutionary relationship between organisms through the similarity of their cDNA.

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cDNA Library Construction

cDNA Library vs. Genomic DNA Library

External links

See also

cDNA Library Construction

cDNA libraries are prepared by first isolating mRNA from cells. Typically these cells are grown in culture or are from tissue samples. Cells can be grown under certain conditions so gene expression under certain conditions can be examined. Cells are harvested and total poly(A)+ mRNA is isolated from cells and stripped of cellular debris. It is then converted into a single-stranded cDNA copy of the message using the enzyme reverse transcriptase. This single-stranded cDNA copy is then hybridized with a primer and DNA Polymerase is used to synthesise the complimentary strand forming double stranded cDNA. The cDNA fragments can be inserted into an appropriate plasmid, phage, or cosmid vector for maintenance and cloning. The population of recombinant vectors will represent the complete, or nearly complete, set of expressed genes in the cell from which the mRNA was isolated.

cDNA Library vs. Genomic DNA Library

In Eukaryotic genomes, the entire sequence of genes is often very large because coding sequence (exons) is interrupted by introns that do not contain coding DNA sequence. The advantage of a cDNA library is that only the exons, or DNA representing expressed sequence, are templates for the creation of DNA (via Reverse Transcriptase) to collect the preferred genes. On the other hand, genes from prokaryotic cells does not usually contain introns, and the DNA is therefore much shorter. Also, prokaryotic mRNA can be difficult to isolate; because of this a genomic library is more preferable for prokaryotic genomic studies.

External links

★ 'cDNA LIBRARY'- Properties, Construction, Isolation & Techniques available for cDNA cloning

★ Functional Annotation of the Mouse database

★ examples of cDNA synthesis and cloning

See also

Genomic library