derDNAReplikation

DerDNAReplikation is the process by which a cell copies its genome prior to division. It is semi-conservative, meaning each daughter molecule inherits one strand from the parent and one newly synthesized strand. In bacteria, replication starts at a single origin and proceeds bidirectionally; in eukaryotes, replication begins at multiple origins along linear chromosomes, proceeding to replicate the entire genome during S phase.

Initiation involves origin recognition and helicase loading. Helicases unwind the double helix, creating a replication fork; topoisomerases relieve torsional strain; single-strand binding proteins stabilize exposed strands. The process sets the stage for priming and synthesis, ensuring that replication proceeds smoothly.

Primase lays RNA primers; DNA polymerases extend from primers in the 5' to 3' direction. The leading strand is synthesized continuously, while the lagging strand is made as short Okazaki fragments that are later joined by DNA ligase. In prokaryotes, DNA polymerase III is the main replicative enzyme; in eukaryotes, DNA polymerases alpha, delta, and epsilon perform priming, elongation, and proofreading.

Proofreading by DNA polymerases minimizes errors; mismatch repair corrects remaining mistakes. RNA primers are removed and replaced with DNA, and gaps are sealed by DNA ligase. Sliding clamps (PCNA in eukaryotes, the beta clamp in bacteria) enhance polymerase processivity and help coordinate synthesis on both strands.

Replication is tightly regulated to occur once per cell cycle and to finish before cell division. Licensing factors such as ORC, Cdc6, Cdt1, and the MCM complex ensure origins fire only once; activation by kinases triggers S-phase replication. Eukaryotic chromosomes also end with telomeres, maintained by telomerase in many cells.