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 phosphorylating MCM helicase.
C)MCM helicase loading by M phase cyclins.
D)G1 cyclin/cdk activation of E2F.

Question

Quizplus · Accepted Answer

During the S phase of the cell cycle, the cyclin-dependent kinase (Cdk) complex phosphorylates the minichromosome maintenance (MCM) helicase, which is essential for DNA replication initiation, allowing it to unwind DNA. The MCM helicase loading by M phase cyclins occurs during G1 phase and is essential for DNA replication initiation. Although ORC guides the initial binding of the pre-RC to origins, it does not prevent re-replication; that is the role of the licensing factors Cdc6p and Cdt1p, which are destroyed during S phase. Similarly, G1 cyclin/cdk activation of E2F only regulates the expression of genes involved in DNA replication, not the initiation of replication itself.

DNA Replication at Each Origin Occurs Only Once During the Cell