Our genes are made of deoxyribonucleic acid (DNA). This remarkable molecule contains all the information necessary to make a cell, and DNA is able to pass on this information when a cell divides. This chapter describes the structure and properties of DNA molecules, the way in which our DNA is packaged into chromosomes, and how the information stored within DNA is retrieved via the genetic code.

Deoxyribonucleic acid is an extremely long polymer made from units called deoxyribonu-cleotides, which are often simply called nucleotides. These nucleotides differ from those described in Chapter 2 in one respect: the sugar is deoxyribose, not ribose. Figure 4.1 shows one deoxyribonucleotide, deoxyadenosine triphosphate. Note that deoxyribose, unlike ribose (page 29), has no OH group on its 2' carbon. Four bases are found in DNA; they are the two purines adenine (A) and guanine (G) and the two pyrimidines cytosine (C) and thymine (T) (Fig. 4.2). The combined base and sugar is known as a nucleoside to distinguish it from the phosphorylated form, which is called a nucleotide. Four different nucleotides join to make DNA. They are 2'-deoxyadenosine-5'-triphosphate (dATP),

Cell Biology: A Short Course, Second Edition, by Stephen R. Bolsover, Jeremy S. Hyams, Elizabeth A. Shephard, Hugh A. White, Claudia G. Wiedemann ISBN 0-471-26393-1 Copyright © 2004 by John Wiley & Sons, Inc.

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