Which mechanism of DNA replication requires cleavage of the sugar-phosphate backbone on a single strand of the DNA?

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BlackTom AI · Accepted Answer

To tackle this question, I’ll compare the replication mechanisms listed and identify which one specifically requires a nick, or cleavage, in the sugar-phosphate backbone of a single DNA strand.
Option 1: Linear chromosome replication. In linear chromosome replication (as seen in eukaryotes), replication begins at origins and proceeds bidirectionally with replication forks, using RNA primers and DNA polymerases. This process does not rely on cleavage of a single DNA strand’s backbone as an initiation step, so this option is incorrect.
Option 2: Theta replication. Theta replication occurs in many prokaryotic plasmids and chromosomes and forms a theta-shaped intermediate during the bidirectional unwinding and synthesis. The initiation involves origin-specific unwinding and primer synthesis but not a required nick in one strand’s backbone. Therefore, this option is not the mechanism described by the prompt.
Option 3: Rolling circle replication. This mechanism is characteristic of certain plasmids, viral genomes, and some circular DNA elements. It begins with a site-specific nick in one strand of the circular DNA, creating a 3’ end for continuous polymerase-driven synthesis and displacing a single-stranded tail that is later converted to double-stranded DNA. The essential feature here is the cleavage (nick) of the sugar-phosphate backbone on a single strand, which drives the process. This option fits the description exactly, making it the correct mechanism under the given criterion.
Option 4: All of the above require cleavage of the DNA to be replicated. Since neither linear chromosome replication nor theta replication requires a nick in a single strand as an indispensable initiation step, this blanket statement is incorrect.
In summary, the key distinguishing feature is the prerequisite nick in one strand’s backbone that initiates rolling circle replication, which is not a universal requirement for the other two mechanisms. The comparison shows that only rolling circle replication matches the described mechanism, while the other options fail to meet that criterion.

BIOL_2004_81774_202509 Homework 3

Which mechanism of DNA replication requires cleavage of the sugar-phosphate backbone on a single strand of the DNA?

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