A helix (pl: helixes or helices) is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Helices are important in biology, as the DNA molecule is formed as two intertwined complementary antiparallel helices, and many proteins have alpha helices in what is known as their secondary structures. The word helix comes from the Greek word ἕλιξ, "twisted, curved".
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