In
molecular biology
Molecular biology is a branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, biomolecular synthesis, modification, mechanisms, and interactio ...
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 Augustinians, Augustinian ...
, upstream and downstream both refer to relative positions of
genetic code
Genetic code is a set of rules used by living cell (biology), cells to Translation (biology), translate information encoded within genetic material (DNA or RNA sequences of nucleotide triplets or codons) into proteins. Translation is accomplished ...
in
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
or
RNA
Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...
. 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
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 comp ...
) 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 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.
The terms upstream and downstream are sometimes also applied to a polypeptide sequence, where upstream refers to a region
N-terminal and downstream to residues
C-terminal of a reference point.
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 ...
References
Molecular biology
Orientation (geometry)
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