36 • Impacts of Applied Genetics — Micro-Organisms, Plants, and Animals 
Figure 8.— The Structure of DNA 
8b. The four bases form the four letters in the alphabet of 
the genetic code. The sequence of the bases along the 
sugar-phosphate backbone encodes the genetic in- 
formation. 
A schematic diagram of the DNA double helix. A three-dimensional representation of the DNA double helix 
8c. The DNA molecule is a double helix composed of two chains. The sugar-phosphate backbones twist around the out 
side, with the paired bases on the inside serving to hold the chains together. 
SOURCE; Office of Technology Assessnnent. 
