Double helix (disambiguation)
The double helix (plural double helices; ancient Greek helix, turn ',' spiral ') is a geometric structure, in which - in contrast to the simple helix - the subject of the thread appears twice.
There are two types of double helices:
- Type 1 consists of two umeinanderlaufenden simple helices, it is referred to as two -hand screw (Fig. 1)
- Type 2 is in contrast from only one strand. This is wound into a helix, which is in turn wound into a helix having a larger radius. This type is also called a double helix ( Fig. 2).
In biochemistry, the term double helix is usually used to describe a secondary structure for the type 1. He refers to two parallel strands of macromolecules, the helically revolve around one another. The most prominent example is the structure of occurring in all living things deoxyribonucleic acid molecule. The course of the DNA strands is here additionally opposite ( anti-parallel ). The actual helices are formed from the backbone of DNA, composed of phosphates and sugars. The so-called " bars " are bases that connect the two single strands by hydrogen bonding.
The DNA double helix is often misrepresented as a double strand, in which the individual strands interlocking orbit (see Figure 1, red / blue). In fact, however, about a common axis both strands run parallel to each other ( see figure below). In this arrangement, the major and minor grooves of the DNA are visible which are not visible in the simplified representation.
Within the chromosomes of these DNA duplexes are again compressed spirally arranged around nucleosomes, which are in turn presumably spirally wound in a "super- super helix ".
A special form of the double helix is found in the structure of keratins in actin filaments. The special feature of this structural protein is that the individual strands are wound in this double helix of type 1 itself into a helix, for themselves so represent a double helix of type 2.
In such cases, one speaks of a coiled-coil structure in which up to seven individual strands may be involved.
In filaments in incandescent lamps is type 2 This double helices consist of a coiled wire, which in turn is formed into a spiral again. This makes it possible to accommodate a longer wire for a short distance, so that illuminate the individual turns against each other, which thus increases light output and luminance on the principle of cavity radiation, the emissivity of the forest, and.
One application in architecture is the appropriate arrangement of spiral staircases.
Near the center of the Milky Way is an approximately 80 light-years long plasma cloud is in the form of a double helix in which wind their two fog strands around each other. The longitudinal axis of the gigantic double helix structure here is * aligned on the 300 light- years distant supermassive black hole Sagittarius A at the center of the Milky Way, its extremely strong magnetic field interacts with the matter of the dust cloud.