Upstream and downstream
The terms upstream and downstream are referred to the molecular biology and in the genetics the direction of transcription and the position of nucleotide sequences comprising a coding region ( English coding region surrounded). The coding region must not be confused with the exon or exome , since an exon contains a coding region as well as a 3 ' and 5' untranslated region that does not code for the actual protein.
Each DNA or RNA strand has a 5 ' and 3' end , which refers to certain carbon atoms of the ( deoxy ) ribose . It was determined that upstream or downstream refers to the 5 '→ 3' direction of DNA transcription. The direction of transcription to the 3 'end is referred to as downstream . The opposite direction to the 5 'end is called upstream . In the case of double-stranded DNA, this always depends on the codogenic strand (template strand) of the respective gene. Due to the antiparallelism of the DNA, the upstream and downstream of the non-template strand - viewed from the template strand - are reversed.
The position +1 is assigned to the first transcribed nucleotide ( transcription start point ) . Nucleotides downstream of the start of transcription are assigned positive numbers; those that are upstream from the starting point are given negative positions. A nucleotide assigned the position +34 is located 34 nucleotides downstream from the start of transcription, whereas a nucleotide with the position -75 is located 75 nucleotides upstream from the start of transcription. A nucleotide with position 0 does not exist.
See also
Individual evidence
- ↑ Harvey Lodish: Molecular Cell Biology . Ed .: WH Freeman. 2008, ISBN 978-0-7167-7601-7 , pp. 285 ff . ( limited preview in Google Book search).
- ^ Benjamin A. Pierce: Genetics . A conceptual approach. 5th edition. WH Freeman and Company, 2014, ISBN 978-1-4641-0946-1 , pp. 363 .