The end‑replication problem (telomere problem) exists in eukaryotic chromosomes and is characterized by the chromosomes shorteni
ng with each round of DNA replication. Select the statements that best explain why the end-replication problem exists in eukaryotic chromosomes. 1) The RNA primer is removed in a 3′ to 5′ direction. 2) DNA ligase links the 5′ OH group of one fragment to the 3′ phosphate group of an adjacent fragment. 3) DNA polymerase synthesizes DNA from the phosphate end to the hydroxyl end. 4) DNA polymerase requires a primer for DNA synthesis. 5) The lagging strand is synthesized from the hydroxyl end to the phosphate end.
The correct answers are option 3) "DNA polymerase synthesizes DNA from the phosphate end to the hydroxyl end" and 4) "DNA polymerase requires a primer for DNA synthesis".
Explanation:
The end‑replication problem (telomere problem), refers to the shortening of the telomeres because linear DNA molecules are not entirely replicated by conventional DNA polymerases. Two of the reasons why this problem exists in eukaryotic chromosomes are that DNA polymerase synthesizes DNA from the phosphate end to the hydroxyl end and DNA polymerase requires a primer for DNA synthesis. The incomplete synthesis takes place at the lagging strand during eukaryotic replication, where a RNA primer is needed for the synthesis of the Okazaki fragments and DNA polymerase leaves a 3' hydroxyl group at the end of the sequence. This problem is assessed by the cells with the recruitment of a reverse transcriptase called telomerase that adds telomeric repeats in the unfilled sequences.
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