DNA Replication Tournament
Two onboarding diagrams place DNA replication inside the cell cycle. Then eight MCAT-DoK rounds: Okazaki fragments and lagging-strand logic, fluoroquinolone gyrase inhibition, Meselson-Stahl, the replisome enzymes in order, bidirectional replication timing, eukaryotic-specific features, and the Hayflick / telomerase story.
Where the S phase (DNA replication) fits in Cell cycle (mitotic)
DNA replication happens during S phase of the cell cycle - flanked by G1 and G2 quality-control checkpoints. To enter the tournament, click the highlighted S phase box.
Click the highlighted S phase (DNA replication) box to continue.
What this tournament tests
Each task maps to a distinct MCAT cognitive demand. The first two orient you in the broader topology; the next eight test the high-yield mechanism, regulation, sequence and quantitative reasoning that consistently appear on test day.
The Bigger Picture
Locate DNA replication inside Reactome's mitotic cell-cycle map (S phase).
Whole-Pathway Overview
Pan and zoom the WikiPathways DNA-replication figure before you play.
Fill in the Blank
Recall the lagging-strand Okazaki-fragment solution to 5' -> 3' polymerization.
Disruptor
Predict the consequence of fluoroquinolone (gyrase) inhibition on bacterial fork progression.
Sequence Ordering
Order the events at the fork from origin recognition to ligase-sealed nick.
Match the Pairs
Pair each replication enzyme/protein (helicase, primase, polymerase, ligase, telomerase) to its function.
Numeric Input
Compute the ~2300 sec doubling time of E. coli's circular chromosome under bidirectional replication.
Select All That Apply
Identify true facts about EUKARYOTIC replication (multiple origins, S-phase only, etc.).
Odd One Out
Distinguish replisome activities from post-replication repair (mismatch repair).
Hayflick Limit
Recall how somatic telomere erosion sets a finite division ceiling - and how cancer escapes it.
Public leaderboard
Your score posts to a global, persistent leaderboard scored by points first, time as tiebreaker.
DNA replication in 60 seconds
Replication is semi-conservative (Meselson-Stahl), proceeds 5' -> 3' only, and is bidirectional from each origin. Two forks per origin. The leading strand is continuous; the lagging strand is built as Okazaki fragments that are later joined by ligase.
The replisome cast: helicase (unwinds); topoisomerase II / gyrase (relaxes the supercoils generated ahead of the fork; targeted by fluoroquinolones); SSB / RPA (stabilize ssDNA); primase (lays RNA primers); Pol III (E. coli) or Pol δ / ε (eukaryotes); RNase H + FEN1 + Pol I (primer removal); DNA ligase (seals nicks).
Eukaryotic-specific features: linear chromosomes, multiple origins per chromosome, S-phase-only firing (licensing via ORC + Cdc6 + Cdt1, fired by S-CDK), and the end-replication problem solved by telomerase in stem / germ / cancer cells. Somatic cells without telomerase shorten by ~50-100 bp per division and reach the Hayflick limit after ~50 divisions.
Fidelity: base-selection (10^-5) + 3' -> 5' proofreading (10^-7) + mismatch repair after replication (10^-9 to 10^-10) cumulatively give E. coli its astonishing one-error-per-genome replication rate.
FAQ
Why are fluoroquinolones bactericidal at low doses?
They inhibit DNA gyrase (topoisomerase II in eukaryotes) and topoisomerase IV. With supercoils unrelaxed, the replication fork stalls and double-strand breaks accumulate. Bacteria die as soon as they next try to replicate.
What is the Hayflick limit?
The maximum number of divisions a somatic cell can undergo (~50) before reaching replicative senescence. Driven by progressive telomere erosion. Stem cells, germ cells, and ~85-90% of cancers re-express telomerase to evade the limit.
Do I need an account to play?
No. The tournament is fully public. You get a randomized handle and your score posts to the public leaderboard at the bottom of this page.
Keep going
Pol II, capping, splicing, polyadenylation - and where α-amanitin breaks the system.
Ribosomes, codon-anticodon, antibiotic targets, and the unique chemistry of the ribozyme PTC.
Overview diagram: Reactome Pathway R-HSA-69278, licensed CC BY 4.0.