In
molecular biology
Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...
and
genetics
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar work ...
, upstream and downstream both refer to relative positions of
genetic code in
DNA or
RNA. Each strand of DNA or RNA has a
5' end
Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. In a single strand of DNA or RNA, the chemical convention of naming carbon atoms in the nucleotide pentose-sugar- ...
and a
3' end, so named for the carbon position on the
deoxyribose (or
ribose
Ribose is a simple sugar and carbohydrate with molecular formula C5H10O5 and the linear-form composition H−(C=O)−(CHOH)4−H. The naturally-occurring form, , is a component of the ribonucleotides from which RNA is built, and so this com ...
) ring. By convention, upstream and downstream relate to the 5' to 3' direction respectively 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
When referring to DNA transcription, the coding strand (or informational strand) is the DNA strand whose base sequence is identical to the base sequence of the RNA transcript produced (although with thymine replaced by uracil). It is this 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.
Some genes on the same DNA molecule may be transcribed in opposite directions. This means the upstream and downstream areas of the molecule may change depending on which gene is used as the reference.
See also
*
Upstream and downstream (transduction)
The upstream signaling pathway is triggered by the binding of a signaling molecule, a ligand, to a receiving molecule, a receptor. Receptors and ligands exist in many different forms, and only recognize/bond to particular molecules. Upstream ex ...
References
Molecular biology
Orientation (geometry)
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