Lecture 11_250 review

Exam 2 Review Topics

Lecture 11: DNA Replication

Prokaryote Replication

• Initiation

  • Bidirectional, semiconservative: DNA replication occurs in two directions and conserves half of the original DNA strand.

  • Control: The replication process is tightly regulated to ensure accuracy.

  • Components involved:

    • OriC: The origin of replication in prokaryotes.

    • Initiator: Protein that recognizes and binds to OriC to start replication.

    • Helicase Loader: Facilitates the loading of helicase onto DNA.

    • Helicase: Unwinds the DNA helix at the replication fork.

    • SSB proteins: Single-strand binding proteins that stabilize unwound DNA.

    • Dna primase: Synthesizes short RNA primers needed for DNA synthesis.

    • Replication forks and replication bubble: Sites where DNA is unwound and replication occurs.

  • DnaA interaction with OriC: DnaA binds to OriC, initiating the unwinding of DNA.

• Elongation

  • DNA polymerases in prokaryotes: Prokaryotes have three different DNA polymerases.

  • Synthesis direction: DNA synthesis occurs in the 5' to 3' direction.

  • Function of polymerases:

    • DNA Pol I: Removes RNA primers and fills gaps.

    • DNA Pol II: Involved in DNA repair processes.

    • DNA Pol III: Main enzyme for DNA synthesis during replication.

    • RNase H: Removes RNA primers.

    • DNA ligase: Joins Okazaki fragments on the lagging strand.

    • DNA gyrase: Relieves torsional strain ahead of the replication fork.

  • Leading vs. Lagging Strand

    • Leading strand: Synthesized continuously in the same direction as the replication fork.

    • Lagging strand: Synthesized in short segments (Okazaki fragments) away from the fork.

• Termination

  • Ter and Tus: Proteins that help terminate replication by preventing further elongation.

  • Catenane links: Circular linked DNA molecules resolved by topoisomerase IV to separate them.

Eukaryote Replication

• Differences from prokaryotes

  • Linear genome: Eukaryotic DNA is linear compared to circular in prokaryotes.

  • Similarities: Still bidirectional and semiconservative.

  • Origin of replication: Eukaryotes have multiple origins of replication to accommodate larger genomes.

• DNA Replication

  • Initiation

    • ORC role: Origin recognition complex initiates the formation of the replication machinery.

  • Elongation

    • Polymerases and roles: Multiple DNA polymerases are involved in the replication process.

    • RNase H role: Removes RNA primers during eukaryotic replication.

  • Termination

    • End-replication problem: Issue arising due to incomplete replication of the ends of linear DNA.

    • Production of overhangs: Result of the inability to fully replicate chromosome ends.

• Telomere: Structure at the end of a chromosome that protects it from deterioration.

• Telomerase role: Enzyme that extends telomeres, allowing for complete replication of chromosome ends.