replication

Replication results in the copy of the DNA double helix, and, like transcription, proceeds 3' to 5' on the template strand and 5' to 3' on the replica strand. Replication is "semi-conservative" in that each new DNA double helix contains one of the original "parental" strands along with a newly synthesized strand.

Other possibilities for replication would have been
1. Fully conservative replication, with an original parental strand plus a complete new double stranded copy, or
2. Fully nonconservative replication ("dispersive") with disassembly, copying of fragments, and reassembly into two new randomly mixed strands each containing sections of the original and copied segments.)

Helicases are a critical part of the DNA replication process because they unwind double-stranded DNA to create single strands suitable for copying by the replication machinery. This and other helicase activity in the cell depends on the ability of the helicase's protein “engine” to crawl along the DNA strand. This locomotion is powered by ATP, the cell's ubiquitous energy source. Helicase ProteinA helicase protein moves rapidly on a highly flexible single-stranded DNA track. Repetitive movement on the DNA may keep it clear of potentially toxic proteins. Watch Animation 8KB Flash Animation(requires Flash Player)

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