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Replication Initiation in Eukaryotes

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Questions and Answers

What is the role of the Origin Recognition Complex (ORC) in eukaryotic DNA replication?

It phosphorylates the DNA polymerase during replication.

It binds to the origin of replication and recruits helicase loading proteins. (correct)

It directly initiates DNA synthesis.

It directly unwinds the DNA strands for replication.

What triggers the unwinding of DNA during the S phase of the cell cycle?

Binding of DNA polymerase to the ORC.

Activation of helicase via cyclin dependent kinase. (correct)

Phosphorylation of the replicator sequence.

Loading of helicase without any additional proteins.

What prevents the recruitment of additional helicase during the S phase?

Activation of cyclin dependent kinase and phosphorylation of ORC components. (correct)

Dissociation of helicase loader proteins.

Formation of the prereplicative complex in G1 phase.

Completion of DNA replication.

In which phase of the cell cycle does DNA replication occur?

<p>S phase only.</p> Signup and view all the answers

Which of the following accurately describes the ARS in yeast?

<p>It serves as a binding site for the Origin Recognition Complex.</p> Signup and view all the answers

Study Notes

Replication Initiation in Eukaryotes

Replication is restricted to the S-phase of the cell cycle.
In yeast, the replicator is an ARS (autonomously replicating sequence), which is a binding site for the Origin Recognition Complex (ORC).
The definition of a replicator is less clear in other eukaryotes.
ORC is a 6-protein complex that binds to the origin of replication.
It recruits helicase loading proteins, subsequently bringing in helicase, creating a pre-replicative complex in the G1 phase.
During S-phase, the helicase loading proteins detach, activating the helicase.
DNA unwinding begins, and the replication machinery is recruited.
When cells enter S-phase, the cyclin-dependent kinase (CDK) is activated.
CDK phosphorylates helicase loader proteins and components within the ORC complex.
This prevents further helicase recruitment, ensuring each origin fires only once per cell cycle.

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Description

This quiz covers the key concepts of replication initiation specifically in eukaryotic cells. It explores the role of ARS and the Origin Recognition Complex, along with the events that take place during the cell cycle’s S-phase. Test your understanding of how helicase and other proteins function during DNA replication.