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Introduction to Heterocycles

DNA - Deoxyribonucleic Acid

Section of a DNA molecule.

Deoxyribonucleic acid (DNA), which carries genetic information in all living beings, contains the nitrogen-containing heterocycles adenine and guanine (purine bases), as well as cytosine and thymine (pyrimidine bases). Ribonucleic acid (RNA) additionally contains the pyrimidine base uracil. Genetic information is saved in the sequence of these purine and pyrimidine bases in the DNA and RNA chains.

Genes consist of double-stranded DNA. Each DNA strand is composed of a long chain of alternating deoxyribose (blue) and phosphate (green) residues. Each deoxyribose carries a purine or a pyrimidine base (red). In the double-stranded DNA, two of these DNA strands are twined together. As a result, a double-helix structure is obtained. The two DNA strands are held together by hydrogen bridge bonds between the purine and pyrimidine bases. The double-helical structure enables only two different base pairs. The purine base adenine (A) of one DNA strand is always connected with the pyrimidine base thymine (T) of the other DNA strand, while the purine base guanine (G) is always combined with the pyrimidine base cytosine. Thus, only the two base pairs AT and GC appear in double-helical DNA molecules. These base pairs are known as Watson-Crick base pairs, named after James Watson and Francis Crick, who elucidated the DNA structure in 1953. Try to discover the double-helical DNA's structure by manipulating the interactive, three-dimensional molecular model below with your mouse (Chime).

DNA (3D representation)
This 3D molecule is from a DNA-Tutorial

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