Genomic library and cDNA library

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What is a DNA Library

Genomic Library: Bank of DNA that represents the genome of
specific cell/organism/species

cDNA Library: Bank of cDNA representing mRNA of a specific cell.

Originally libraries made in vectors- allow replication in E.Coli

Later, linker libraries for PCR based cloning-

”Marathon Libraries”



Genomic Library:

ways to make a genomic library:

Complete digestion (at all relevant restriction sites)

Produces a large number of short DNA clones.
Genes containing two or more restriction sites may be cloned in two or more pieces.

Mechanical shearing

Produces longer DNA fragments.
Ends are not uniform, requires enzymatic modification before fragments can be inserted into a cloning vector.

Partial digestion



cDNA Library:

cDNA is derived from mature mRNA, does not include introns.

cDNA may contain less information than the coding region.

cDNA library reflects gene activity of a cell at the time mRNAs are isolated (varies from tissue to tissue and with time).

mRNA degrades quickly after cell death, and typically requires immediate isolation (cryoprotectants can increase yield if immediate freezing is postponed by field work).

Creating a cDNA library:

Isolate mRNA

Synthesize cDNA

Clone cDNA