In terms of biochemistry, a DNA strand is a polymer—a large molecule built from repeating units. The units in DNA are composed of 2'-deoxyribose (a five-carbon sugar), phosphoric acid, and the four nitrogen- containing bases denoted A, T, G, and C. The chemical structures of the bases are shown in Figure 2.3. Note that two of the bases have a double-ring structure; these are called purines. The other two bases have a single-ring structure; these are called pyrimidines.
• The purine bases are adenine (A) and guanine (G).
• The pyrimidine bases are thymine (T) and cytosine (C).
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| Pyrimidines |
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| Purines |
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| Nucleoside & Nucleotide |
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