How does a genomic library differ from a cDNA library?

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DNA extraction and recombinant DNA technology — recombinant DNA The process of DNA extraction is necessary to isolate molecules of DNA from cells or tissues. A series of steps, including the use of protease enzymes to strip proteins from the DNA, are required for isolating pure DNA that is suitable for use in later procedures, such as cloning or sequencing.

In the context of recombinant DNA technology, genomic and cDNA libraries differ primarily in their source material and the genetic information they represent:

Genomic Library: This library is created by extracting total DNA from an organism and fragmenting it. It contains the entire genome, including both coding sequences and non-coding regions, such as introns and untranscribed DNA.1
cDNA Library: This library is created using messenger RNA (mRNA) as the starting material. The enzyme reverse transcriptase is used to synthesize complementary DNA (cDNA) from the mRNA. Consequently, a cDNA library represents only the genes that were actively transcribed into mRNA at the time of extraction, excluding non-transcribed regions.1

Because genomic DNA from eukaryotes contains introns that cannot be processed by bacteria, cDNA is often preferred for studies involving gene expression, as it allows for the production of eukaryotic proteins in bacterial cells when used in expression libraries.1