## DNA Helicase: The Unwinding Enzyme ### Function Helicase is the enzyme that unwinds the DNA double helix by breaking hydrogen bonds between complementary base pairs, creating the replication fork and allowing access to the template strands. ### Key Point: **Key Point:** Helicase uses ATP hydrolysis to provide energy for breaking hydrogen bonds and separating the two DNA strands during replication. ### Mechanism Helicase works in the 5' → 3' direction along the template strand, progressively unwinding the helix ahead of DNA polymerase. This creates single-stranded DNA (ssDNA) that is stabilized by single-strand binding proteins (SSB proteins). ### High-Yield: **High-Yield:** In prokaryotes, DnaB helicase is the primary replicative helicase. In eukaryotes, MCM2-7 complex serves this function. Both are essential for initiating and maintaining DNA replication. ### Distinction from Other Enzymes | Enzyme | Function | |--------|----------| | **Helicase** | Unwinds double helix; breaks H-bonds | | DNA Polymerase III | Synthesizes new DNA strand | | Primase | Synthesizes RNA primers | | Ligase | Joins Okazaki fragments | ### Clinical Pearl: **Clinical Pearl:** Defects in helicase function are associated with Xeroderma Pigmentosum (XP) and Werner syndrome, leading to impaired DNA repair and increased cancer risk.
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