In
molecular biology and
genetics,
upstream and
downstream both refer to a relative position in
DNA or
RNA. Each strand of DNA or RNA has a
5' end and a
3' end, so named for the carbon position on the
deoxyribose (or
ribose) ring. By convention, upstream and downstream relate to the 5' to 3' direction in which RNA
transcription takes place. Upstream is toward the 5' end of the RNA molecule and downstream is toward the 3' end. When considering double-stranded DNA, upstream is toward the 5' end of the
coding strand for the gene in question and downstream is toward the 3' end. Due to the anti-parallel nature of DNA, this means the 3' end of the
template strand is upstream of the gene and the 5' end is downstream.