High temperature about $94^{\circ}C$ is required for the process of denaturation which is the first step of PCR. Ligation of DNA fragments is performed with the help of an enzyme called DNA ligase. Annealing is performed at $50^{\circ}C-60^{\circ}C$ which is the second step that can get affected. Addition of nucleotides to the primer, synthesizing a new DNA strand using only the template sequences with the help of DNA polymerase is called primer extension/polymerisation.