Upstream and downstream (DNA)

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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 carbons on the deoxyribose (or ribose) ring. Relative to the position on the strand, downstream is the region towards the 3' end of the strand. Since DNA strands run in opposite directions, downstream on one strand is upstream on the other strand.

Upstream and downstream.svg

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Transcription and translation of DNA and mRNA, respectively, have their direction defined by the newly synthesized strand, that is, in downstream direction (5' → 3'). However, it is in the upstream direction (3' → 5') for the copied template strand.

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