D1.1 HL Details of DNA Replication (Prokaryote)
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Key words for Prokaryotic replication (extra details):
Prokaryotic circular DNA Origin of replication (oriC) Bidirectional replication Two replication forks DNA gyrase (topoisomerase) Torsional strain
key words for Enzyme functions (extended):
Helicase → unwinds helix, breaks hydrogen bonds Primase → lays down RNA primers DNA polymerase III → extends strand, uses dNTPs, requires free 3′-OH group DNA polymerase I → removes RNA primers, replaces with DNA nucleotides DNA ligase → seals nicks between Okazaki fragments, forms phosphodiester bonds
key words for Directionality:
5′ → 3′ synthesis 3′ → 5′ template reading Free 3′-OH group Okazaki fragments Multiple primers on lagging strand
Ket words for Proofreading / Accuracy:
Proofreading activity Exonuclease function Error correction Fidelity Mutation prevention
key words for Applications / Connections:
Antibiotics targeting DNA gyrase or DNA polymerase PCR (polymerase chain reaction) DNA sequencing
Helicase?
Unwinds and separates double-stranded DNA.
DNA primase?
Synthesizes RNA primer for DNA polymerase to start replication.
DNA polymerase III?
Extends RNA primer with DNA nucleotides.
DNA primase?
Synthesizes RNA primer for DNA polymerase to start replication.
DNA polymerase I?
Removes RNA primers and replaces them with DNA.
DNA ligase?
Joins Okazaki fragments on lagging strand.
Topoisomerase?
Relieves tension by breaking and rejoining DNA ahead of fork.
What is the significance of 3’ and 5’ ends?
Polymerase adds nucleotides to 3’ end → replication is directional.
Why is proofreading essential?
Maintains DNA sequence fidelity, prevents mutations.
Leading strand vs lagging strand synthesis?
Leading = continuous, one primer; Lagging = discontinuous, multiple primers, Okazaki fragments.
Explain DNA proofreading.
DNA polymerase detects mismatches, removes incorrect nucleotides (3’-5’ exonuclease), mismatch repair fixes remaining errors.
How is CRISPR-Cas9 related to DNA replication?
Uses DNA repair and ligation mechanisms to insert new sequences.
Why is semi-conservative replication advantageous evolutionarily?
Conserves original DNA template → reduces mutation rate, ensures accurate inheritance.
How does directionality impact drug targeting in antibiotics?
Some antibiotics inhibit bacterial DNA polymerase → prevents replication
Why is it called “semi-conservative”?
Because half of the original DNA is conserved in each new molecule.
What does “semi-conservative replication” mean?
Each new DNA molecule has one original (parent) strand and one newly synthesized (daughter) strand.
How did Meselson and Stahl prove semi-conservative replication?
Grew bacteria in heavy N → transferred to light N → after one generation, DNA was intermediate; after two, half intermediate, half light.
What would be seen if replication were conservative instead?
One molecule entirely original DNA, one entirely new DNA; no intermediate.
Which strand is synthesized continuously during replication?
Leading strand.