Overview Nitrogenous bases purines structure 2 rings examples adenine (A), guanine (G) found in DNA and RNA xanthine, hypoxanthine, uric acid not found in either DNA or RNA pyrimidines structure 1 ring examples cytosine (C) found in DNA and RNA thymine (T) found in DNA uracil (U) found in RNA Nucleoside nitrogenous base + ribose Nucelotide nitrogenous base + ribose + phosphate 3'-5' phosphodiester bond connects ribose and phosphate DNA nucleotide interactions H-bonding G with C 3 H-bonds stronger A with T 2 H-bonds weaker A with U in RNA melting or denaturing H-bonds disrupted with changes in temperature, pH, chemical agents ↑ GC content = ↑ melting temperature DNA can form correct structure again if disrupting agent is removed slowly (reanealing) key principle of Southern blotting and PCR see Biological lab techniques section strands antiparallel right handed double helix Chargaff's rules A % = T/U % G % = C % Clinical importance anticancer drugs can intercalate DNA daunorubicin, doxorubicin can bind DNA cisplatin