FIGURE 5-29 Leading-strand and lagging-strand DNA synthesis. Nucleotides are added by a DNA polymerase to each growing daughter strand in the 5′→3′ direction (indicated by arrowheads). The leading strand is synthesized continuously from a single RNA primer (red) at its 5′ end. The lagging strand is synthesized discontinuously from multiple RNA primers that are formed periodically as each new region of the parent duplex is unwound. Elongation of these primers initially produces Okazaki fragments. As each growing fragment approaches the previous primer, that primer is removed and the fragments are ligated. Repetition of this process eventually results in synthesis of the entire lagging strand.