Doppelstrang
Doppelstrang is a term used in biology to refer to a molecule composed of two nucleic acid strands that are complementary and held together by base pairing. The most familiar example is double-stranded DNA, but double-stranded RNA also exists in some viruses and cellular processes. In a typical double-stranded molecule, the two polynucleotide chains run antiparallel, one from the 5' end to the 3' end and the other in the opposite direction. The sugar-phosphate backbones are on the outside, while the bases pair inside: adenine with thymine (or uracil in RNA) and guanine with cytosine. This arrangement forms a double helix in many conditions, most commonly the right-handed B-form in DNA, with major and minor grooves that proteins recognize for regulation and replication. The term "double strand" can also describe alternative DNA forms, such as Z-DNA, which adopts a left-handed helix under certain conditions, and double-stranded RNA, which generally adopts an A-form geometry.
Biologically, the double-stranded arrangement is crucial for storing genetic information and for faithful replication. During cell