DNA Double Helix

DNA Double Helix

In Molecular Biology, the double helix refers to the structure of DNA. The DNA double helix is a right-handed spiral polymer of nucleic acids, held together by nucleotides which base pair together. A single turn of the helix constitutes ten nucleotides. The double helix structure of DNA contains a major groove and minor groove, the major groove being wider than the minor groove. Given the difference in widths of the major groove and minor groove, many proteins which bind to DNA do so through the wider major groove.

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Double-Stranded Helical Model
Double-Stranded Helical Model
The easiest way to visualize DNA is as an immensely long rope ladder, twisted into a cork-screw shape. The sides of the ladder are alternating sequences of deoxyribose and phosphate (backbone) while the rungs of the ladder (bases) are made in two parts with each part firmly attached to the side of the ladder.
Alternative Double-Helical Structures
Alternative Double-Helical Structures
DNA exists in many possible conformations. However, only A-DNA, B-DNA, and Z-DNA have been observed in organisms. Which conformation DNA adopts depends on the sequence of the DNA, the amount and direction of supercoiling, chemical modifications of the bases and also solution conditions, such as the concentration of metal ions and polyamines. Of these three conformations, the "B" form described above is most common under the conditions found in cells. The two alternative double-helical forms of DNA differ in their geometry and dimensions.
Three-Helical Structure
The scientist Linus Pauling was eager to solve the mystery of the shape of DNA. In 1954 he became a Nobel Laureate in Chemistry for his ground-breaking work on chemical bonds and the structure of molecules and crystals. DNA is a winning formula for packaging genetic material. Therefore almost all organisms – bacteria, plants, yeast and animals – carry genetic information encapsulated as DNA. One exception is some viruses that use RNA instead.
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