(1) The four nitrogen bases constitute the genetic alphabet. They form the
blueprints for cell reproduction and are the building blocks of life. Figure 4-12 is an
example of an unwound DNA molecule. Notice that the sugar phosphate chain forms
The weakest link in this complex chain is the point where the nitrogen bases join
together. This is a hydrogen bond, one of the weakest chemical bonds known. Also
note the sequence of the nitrogen bases in figure 4-12. Each variety of cell will have a
certain sequence. This sequence is the critical factor when the DNA molecule performs
its two functions--replication and control of cellular activity.
Figure 4-12. Segment of DNA molecule unwound.