1. DNA is the master molecule of the cell and carries all of the cell's genetic information in its sequence of nucleotides.
2. DNA is a double-stranded helical molecule with a backbone composed of covalently bonded sugar and phosphate groups. The purine and pyrimidine bases extend into the center of the helix. (Figure 2.25a)
3. The two strands of DNA are complementary and are held together by hydrogen bonds between the bases.
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