base(A, G, C, or T) HO一P—0—P-0—P—0—CH OH b annealed primer growing end of DNA 50 OH 3 template strand Ac GTCGACGIT C GAco IT C GACGT 3 HO ⊙5 dsDNA SSDNA Figure 8-3 Substrates required for DNA synthesis.Figure 8-3 Substrates required for DNA synthesis