Question

Which of the following statements about initiation of DNA replication in eukaryotes is/are true?

• A. DNA replication is initiated at the origin of replication licensed by loading of Mcm helicase complex
• B. Loading of Mcm helicase complex takes place in S phase
• C. Mcm helicase complex are activated by S-Cdks
• D. Mcm helicase complex is responsible for loading of origin recognition complex

Hint:

The Mcm helicase complex is essential for unwinding DNA during replication and is activated by cyclin-dependent kinases (S-Cdks).

Answer 1

The Correct Option is A, C

In eukaryotic DNA replication, several key steps occur to initiate the process at the origin of replication:

Step 1: Licensing of the origin
DNA replication is initiated at the origin of replication. The Mcm helicase complex is loaded onto the DNA in the G1 phase to "license" the origin for replication.
Thus, \( \boxed{A} \) is correct.

Step 2: Activation of Mcm helicase complex
The Mcm helicase complex is activated by S-Cdks (cyclin-dependent kinases in the S phase). This activation is a crucial step to start unwinding the DNA at the replication fork.
Thus, \( \boxed{C} \) is correct.

Step 3: Loading of Mcm helicase complex
The loading of the Mcm helicase complex occurs during the G1 phase, not in the S phase.
Therefore, \( \boxed{B} \) is incorrect.

Step 4: Origin recognition complex
The origin recognition complex (ORC) is responsible for the initial binding to the origin of replication and for recruiting the Mcm helicase complex.
Therefore, \( \boxed{D} \) is incorrect.

Final Answer:
The correct answers are \( \boxed{A}, \boxed{C} \).