Question

DNA replication at each origin occurs only once during the cell cycle because of:

a) specificity of the origin-recognition complex (ORC)

b) S phase CDK phoshporylating MCM helicase

c) MCM helicase loading by M phase cyclins

d) G1 cyclin/CDK activation of E2F

Answer 1

A is the correct answer

To mantain genome integrity, the cell has a regulating mechanism that allows the occurence of DNA Replication event only once during each cell cycle at each origin

This replication licensing is drived by a group of molecules that regulates the replication process

This molecules are CDK , initiator proteins of ORC and MCM complex( microchromosome maintenance complex)

The process occurs in 2 steps:

1- ORC proteins forms a pre replicative complex in late mitosis and early G1 phase

2- proteins of MCM complex initiate origin firing and DNA replication initiates in S phase.