QuestionSBA
QuestionChoice
Due to the twisting nature of DNA, the progression of the replication fork rapidly causes super-coiling of the DNA which halts further progression unless topoisomerases cut the DNA and unwind it. Topoisomerase 1 cuts a single strand to unwind single DNA double helices, whilst topoisomerase 2 cuts both strands of the double helix to allow another to pass through to unwind the super-coiling. Topoisomerase inhibitors, therefore, inhibit replication fork progression and are used as antibiotics and chemotherapeutics.
10001126
a
Replication fork progression
QuestionChoice
DNA polymerase 3 is the leading strand DNA polymerase in bacterial DNA replication. Its continuous activity without dissociation during the replication of the leading strand is facilitated by its association with the sliding B-clamp processivity factor. Topoisomerases are not directly involved in this process.
10001129
d
DNA polymerisation
QuestionChoice
DnaG is the bacterial primase which adds a single RNA primer to the leading strand and numerous RNA primers to the lagging strand to prime each Okazaki fragment. Topoisomerases are not directly involved in this process.
10001128
c
Priming by an RNA primer
QuestionChoice
In bacteria, primers are replaced by DNA polymerase 1 which mediates nick translation. This involves the removal of RNA nucleotides and replacement with DNA nucleotides in the 5' to 3' direction. Once DNA polymerase 1 dissociates, the strands are re-joined by DNA ligases. Topoisomerases are not directly involved in this process.

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10001130
e
Primer replacement
QuestionChoice
DnaA is the origin recognition complex used to bind DnaA boxes, unwind AT-rich regions and load DnaC. This loads the DnaB helicase and then the DnaG primase, the DNA polymerase 3 holoenzyme and the B-clamp processivity factors to form the bacterial DNA replication complex. Topoisomerases are not directly involved in this process.
10001127
b
Binding of DnaA to bacterial origins
Concept
Chapter
2693
3887
Antibiotics
Topic
148
Microbiology
12772
Topoisomerase inhibitors prevent which part of DNA replication?
a