1. FIGURE 4.1. 2-deoxyadenosine-5-triphosphate.

2. FIGURE 4.2. The four bases found in DNA.

3. FIGURE 4.3. The phosphodiester link and the sugar-phosphate backbone of DNA.

4. FIGURE 4.4. The DNA double helix is held together by hydrogen bonds.

5. FIGURE 4.5. How DNA is packaged into chromosomes.

6. FIGURE 4.6. A spread of human chromosomes (at metaphase-see page 298). The orange signal reveals the gene called FMO3,which when mutated causes imethyl- aminuria (fish odor syndrome). There are two copies of the gene, one inherited from each parent, indicated by the arrows. The FMO3 gene is located on the long arm of chromosome 1, the longest human chromosome.

7. FIGURE 4.7. DNA makes RNA makes protein: the central dogma of molecular biology.

8. FIGURE 4.8. The genetic code. Amino acid side chains are shown in alphabetical order together with the three- and one-letter amino acid abbreviations. Hydrophilic side chains are shown in green, hydrophobic side chains in black; the significance of this distinction is discussed in Chapter 9. To the right of each amino acid we show the corresponding mRNA codons.

9. UNFIGURE 4.1.

10. FIGURE 4.9. Reading frames. The genetic code is read in blocks of three.

11. FIGURE 4.10. Mutations that alter the sequence of bases.