Animation showing the synthesis of the lagging strand of DNA (deoxyribonucleic acid) during replication. The lagging strand is synthesised in small segments, known as Okazaki fragments, rather than in a continuous process as on the leading strand. The process is started by DNA primase (red), which adds a short RNA (ribonucleic acid) primer (blue) to the strand to be synthesised. DNA polymerase III (white) then attaches to the primer and synthesises a new DNA strand from the template strand (bottom). When DNA polymerase III meets another RNA primer it detaches from the DNA. DNA polymerase I (green) then attaches and removes the RNA primer and replaces it with DNA. The gaps between the Okazaki fragments are then joined by DNA ligase (pink).