Study guides › B/B › Biology
DNA Replication, Repair & Chromosomes
Cells copy their genome once per cycle, protect its ends, fix damage, and pack it into chromatin. You will learn the enzymes at the replication fork, how telomeres and repair pathways work, and how chromatin structure controls gene access.
Study this chapter in PrepMed (free)
What this chapter covers
- Semiconservative Replication & the Replication Fork. Fork diagrams with labeled enzymes and 5'/3' ends appear again and again on the MCAT.
- Leading Strand, Lagging Strand & Proofreading. Okazaki fragments, primer removal, and the sliding clamp explain why replication is accurate and processive.
- Telomeres & Telomerase. Linear chromosomes shorten every division unless telomerase steps in, which links replication to aging and cancer.
- Mutations & DNA Repair. Know each mutation type by its effect on the protein and each repair pathway by the damage it fixes.
- Chromatin & Chromosome Structure. How tightly DNA is packed decides whether genes can be read, and histone tail chemistry is the switch.
Key points to know
- Replication is semiconservative (Meselson-Stahl)
- Helicase unwinds, SSB stabilizes, topoisomerase relieves supercoils, primase primes
- Leading strand: continuous, toward the fork; lagging strand: Okazaki fragments, away from the fork
- Pol I removes RNA primers; ligase seals nicks
- The end-replication problem affects the lagging-strand 5' end of linear chromosomes
- Telomerase carries its own RNA template and works as a reverse transcriptase
- Silent, missense, nonsense, frameshift: know the protein effect of each
- Uracil in DNA is removed by base excision repair
Try a practice question
Which enzyme breaks the hydrogen bonds between base pairs to open the double helix at the fork?
- Primase
- Helicase
- DNA ligase
- DNA polymerase I
Show the answer
B. Helicase uses ATP to separate the parental strands. Primase makes primers, ligase seals nicks, and polymerase I replaces RNA primers with DNA.
Common questions
What does this chapter cover?
DNA Replication, Repair & Chromosomes covers Semiconservative Replication & the Replication Fork, Leading Strand, Lagging Strand & Proofreading, Telomeres & Telomerase, Mutations & DNA Repair, Chromatin & Chromosome Structure.
What should I know first?
Replication is semiconservative (Meselson-Stahl) Helicase unwinds, SSB stabilizes, topoisomerase relieves supercoils, primase primes Leading strand: continuous, toward the fork; lagging strand: Okazaki fragments, away from the fork
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.