Double Helix DNA and Pentose Sugars

Double Helix DNA

DNA is double stranded helical model for DNA is shown in the graphic on the left. The easiest way to visualize DNA is as an immensely long rope ladder, twisted into a cork screw shape. Sides of the ladder are alternating sequences of deoxyribose and phosphate while the rungs of the ladder are made in two parts with each part firmly attached to the side of the ladder. Parts in the rung are heterocyclic amines held in position by hydrogen bonding. Then most DNA exists as open ended double helices, some bacterial DNA has been found as a cyclic helix. Some time DNA has also been found as a single strand.

Pentose Sugars in DNA
In nucleic acids two types of pentose sugars can be found. This difference is reflected in their names deoxyribonucleic acid indicates the presence of deoxyribose and ribonucleic acid indicates the presence of ribose

These sugars in the graphic on the left, the structures of both ribose and deoxyribose are shown. Note the red OH on one and the red H on the other are the only differences. The alpha and beta designations are interchangeable and are not a significant difference between these tow types