Inactive double hexamers of the replicative helicase core Mcm2–7 are loaded onto origins at the end of mitosis/G1 phase (origin licensing). Origins are activated during S phase with the assembly of the active replicative helicase, also known as CMG (Cdc45-Mcm2–7-GINS), which involves the recruitment of GINS and Cdc45 to the Mcm2–7 complex. While double hexamers of Mcm2–7 encircle dsDNA, CMGs encircle ssDNA and translocate in an ‘N-terminus first' direction thus passing each other within the origin (origin firing). Replisomes are built around CMGs and they progress through the chromatin unwinding DNA and promoting DNA synthesis in a semi-discontinuous way (elongation). Replication forks from neighbouring origins finally converge, leading to complete replication of sister chromatids (termination).