TABLE OF CONTENTS DNA (deoxyribonucleic acid) is a very long, thin, thread-like macromolecule that is made up of a long chain or backbone that is the same (except for length and order) in all nucleic acid molecules. Attached to this backbone at regular intervals are one of four groups that are called bases. The sequence of these bases characterizes the specific nucleic acid. Alternately, we can say that this heteropolymer is made of deoxyribonucleotides a unit that consists of three functional groups: a base, a sugar, and a phosphate group (PO 4). The bases of the DNA molecule carry genetic information, while the sugar and phosphate are important as structural elements. This structure is shown schematically in Fig. 12.6.
The genes of all cells and some viruses are made of DNA. However, some viruses use RNA (ribonucleic acid) as their genetic material. These names follow from the sugars that are part of molecules. The sugar in RNA is D-ribose, while the sugar in DNA is 2-D-deoxyribose. The difference is simple: in RNA there is an OH ? group at a given position, while in DNA a hydrogen atom occupies the same position. The hydrogen in DNA leads to a more stable structure than the OH ? in RNA under physiologic conditions.
The variable part of either a DNA or a RNA molecule is not this backbone but the bases. In both DNA and RNA there...
