Complementary DNA

Complementary DNA (cDNA) is DNA synthesized from an RNA template by reverse transcription. It typically represents a gene’s expressed sequences without introns.

Reverse transcription: The synthesis of DNA from an RNA template by a reverse transcriptase enzyme. It is the process that produces cDNA from RNA.
cDNA library: A collection of cloned DNA copies made from the RNA transcripts present in a sample. A cDNA library preserves a sample’s expressed sequences as a searchable collection.
Messenger RNA: An RNA molecule that carries protein-coding information from DNA to cellular protein-synthesis machinery. Messenger RNA is a common template for making cDNA.
Genomic DNA: The DNA that constitutes an organism’s genome, including genes and noncoding regions. Unlike genomic DNA, cDNA made from mature RNA generally omits introns and regulatory regions.
Reverse transcriptase: An enzyme that synthesizes DNA using an RNA template. This enzyme copies the RNA sequence into cDNA.
RNA-seq: A sequencing method that measures RNA molecules by sequencing DNA copies made from them. Most RNA-seq workflows convert RNA into cDNA before sequencing.
Polyadenylation: The addition of a stretch of adenine nucleotides to the end of many eukaryotic RNA molecules. Poly(A) tails provide binding sites for oligo(dT) primers during cDNA synthesis.
Complementary RNA: An RNA molecule synthesized from a DNA or RNA template by complementary base pairing. cDNA is DNA copied from RNA, whereas complementary RNA remains an RNA molecule.
Oligo(dT): A short DNA primer composed of thymidine nucleotides, designed to bind polyadenylated RNA. It primes cDNA synthesis at the poly(A) tails of many eukaryotic messenger RNAs.
Quantitative polymerase chain reaction: A PCR method that tracks DNA amplification in real time to estimate the amount of a target sequence. Reverse-transcribed cDNA enables qPCR measurement of transcript abundance.

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