DNA is the molecule most commonly referred to as a Double Helix. There are however other types of DNA that do not take this shape, but the majority of the molecules of DNA in the body exist in this manner. The double helix of DNA is called "B-DNA". When we think of RNA, it appears as "half" of a DNA strand - it only has one "staircase". There are times when when two RNA strands are paired, but because of some of the molecular properties, it only forms small helices. These are also short lived, so this form is often ignored. If this was a test question, I would disregard RNA as ever having a helix form - this is just additional information for fun. Carbohydrates are comprised of rings of carbon and oxygen molecules. These rings will often join together to make rather large polymers (such as glycogen). Hope this helps! --SP

1) "The ring form of ribose is a component of ribonucleic acid (RNA). Deoxyribose, which is missing an oxygen at position 2, is a component of deoxyribonucleic acid (DNA). In nucleic acids, the hydroxyl group attached to carbon number 1 is replaced with nucleotide bases." Source and further information: http://www.scientificpsychic.com/fitness/carbohydrates.html 2) "Genetic material in earthly life often contains poly 5′-3′, 2′-deoxyribose nucleotides, in structures called chromosomes, where each monomer is one of the nucleotides deoxy- adenine, thymine, guanine or cytosine. This material is commonly called deoxyribonucleic acid, or simply DNA for short. DNA in chromosomes forms very long helical structures containing two molecules with the backbones running in opposite directions on the outside of the helix and held together by hydrogen bonds between complementary nucleotide bases lying between the helical backbones. The lack of the 2′ hydroxyl group in DNA appears to allow the backbone the flexibility to assume the full conformation of the long double-helix, which involves not only the basic helix, but additional coiling necessary to fit these very long molecules into the very small volume of a cell nucleus. In contrast, very similar molecules, containing ribose instead of deoxyribose, and known generically as RNA, are known to form only relatively short double-helical complementary base paired structures. These are well known, for instance, in ribosomal RNA molecules and in transfer RNA (tRNA), where so-called hairpin structures from palindromic sequences within one molecule." Source and further information: http://en.wikipedia.org/wiki/Deoxyribose