DNA Replication and Key Enzymes

Study Notes

DNA Replication Overview

DNA replication is the process of creating two identical DNA molecules from a single original molecule.
It's crucial for cell division and passing genetic information to daughter cells.

Key Enzymes Involved

DNA polymerase: Adds nucleotides to the growing DNA strand, proofreads for errors.
Helicase: Unwinds the DNA double helix, creating the replication fork.
Primase: Synthesizes RNA primers for DNA polymerase to start replication.
Ligase: Joins Okazaki fragments on the lagging strand.
Single-strand binding proteins (SSBs): Prevent DNA strands from re-annealing.
Topoisomerase: Relieves torsional strain ahead of the replication fork.

Mechanisms of Replication

Semiconservative Replication: Each new DNA molecule has one original and one new strand. Maintains genetic fidelity.
Leading Strand: Synthesized continuously in the 5' to 3' direction.
Lagging Strand: Synthesized discontinuously in Okazaki fragments (5' to 3' direction, opposite of the replication fork). Joined by DNA ligase.

Replication Initiation

Replication starts at specific sites called origins of replication.
Eukaryotic chromosomes have multiple origins to speed up replication of large genomes.
Initiation involves unwinding the DNA double helix and binding replication proteins.

Replication Elongation

DNA polymerase adds nucleotides to the 3' end of the growing strand.
The leading strand replicates continuously, the lagging strand discontinuously.
The process continues as the replication fork moves along the DNA molecule.

Replication Termination

Replication ends at specific termination sequences.
These prevent replication machinery from colliding or causing errors.
Termination ensures complete replication and accurate chromosome separation.

Errors and Repair

DNA polymerase proofreads, minimizing errors.
Occasional errors can still occur.
DNA repair mechanisms correct mistakes (mismatched base pairs, damage).

Importance of Cell Cycle Regulation

DNA replication occurs during the S phase of the cell cycle.
Precise coordination with other cell cycle events is key for accurate replication and division.
Errors in cell cycle control can cause DNA damage, mutations, and diseases (such as cancer).

Description

This quiz explores the process of DNA replication and the key enzymes involved, such as DNA polymerase, helicase, and ligase. Understand the critical roles these enzymes play in ensuring accurate DNA replication for cell division. Test your knowledge on how genetic information is transmitted to daughter cells.