What does antiparallel mean?
Antiparallel describes things that lie parallel to one another but point in opposite directions. In mathematics and physics, two vectors are antiparallel when they have the same line of action but opposite senses, so one is effectively the negative of the other. In biochemistry, the term is essential to describing DNA: the double helix's two sugar-phosphate backbones run antiparallel, one strand running in the 5'-to-3' direction and its partner in the opposite direction, an arrangement that makes complementary base pairing possible. The word also appears in structural biology for antiparallel beta-sheets in proteins and in physics for antiparallel spin alignments in magnetic materials. Though rarely encountered outside technical writing, antiparallel is indispensable in these fields, capturing with a single adjective a precise geometric relationship that ordinary words like 'opposite' or 'parallel' cannot express on their own.
adjectiveParallel but pointing or running in the opposite direction; having lines, vectors, or structures that are parallel yet oppositely oriented.
- (Of vectors or lines) parallel but directed in opposite senses, as in mathematics and physics.
- (Of molecular structures, especially DNA strands or protein beta-sheets) arranged side by side but running in opposite chemical directions.
"The two strands of a DNA double helix run antiparallel to each other."
"In the magnetic material, neighboring electron spins aligned antiparallel, canceling out the overall magnetization."
"The antiparallel arrangement of the beta-strands created a pleated sheet stabilized by hydrogen bonds."
Every twist of your DNA depends on it: the two strands of the double helix only fit together because they run antiparallel — one up, one down.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of antiparallel
Antiparallel combines the Greek-derived prefix 'anti-' (against, opposite) with 'parallel', which itself traces back to Greek 'parallelos' ('beside one another'), from 'para-' (beside) plus 'allelon' (of one another). The word was formed in English as a scientific compound, likely in the nineteenth century as geometry and physics demanded precise terminology for oppositely directed parallels. It shares its roots with related terms such as parallax and antithesis, all drawing on the same Greek building blocks of 'para-' and 'anti-'.
How antiparallel is actually used
A technical term used almost exclusively in scientific contexts — mathematics, physics, biochemistry, and structural biology — rather than everyday speech. It carries no emotional connotation and is neutral in register, though formal by nature of its domain.
Easily confused with antiparallel
Parallel objects point in the same direction along their length, whereas antiparallel objects are parallel in alignment but oriented in opposite directions.