Correct option is C
Explanation-
Statement A: "Camptothecin causes intra-strand and inter-strand crosslinks in DNA, leading to stalling of replication forks." - INCORRECT
Camptothecin does not cause DNA crosslinks. It inhibits Topoisomerase I, leading to single-strand breaks during DNA replication. Crosslinking is caused by agents like cisplatin or mitomycin C, not camptothecin.
Statement B: "Prevention of reinitiation of DNA replication during the same cell cycle is mediated by regulating the loading of the initiator complex ORC." - MISLEADING
Partially correct but misleading.
ORC (Origin Recognition Complex) does initiate replication, but its loading happens in G1 phase. What prevents re-replication in S/G2/M phases is not just ORC, but also inhibition of other components like Cdc6, Cdt1, and licensing factors, regulated by cyclin/CDK levels. So this statement oversimplifies and may mislead if taken strictly.
Statement C: "A glu → ala mutation in the nucleotide building pocket of DNA polymerase III could lead to the incorporation of ribonucleotides in the extending DNA chain." - CORRECT
Glutamate is negatively charged and helps discriminate between dNTPs and rNTPs. Mutation to alanine may lose this specificity, allowing ribonucleotides to be incorporated.
Statement D: "A mutation in the gene encoding Topoisomerase II could lead to entanglement of DNA daughter strands during replication." - CORRECT
Topoisomerase II is essential to decatenate daughter DNA strands. Mutations can impair this and result in chromosome entanglement and segregation defects.
Final Answer:
Correct statements: C and D only
So the right answer is: Option c → C and D only
