Unwinding the Double Helix: Meet DNA Helicase

In previous articles (see herehere and here), I’ve been reviewing the molecular nano-machinery needed for the replication of DNA. Before DNA polymerase is able to synthesize the new complementary strands, it needs to be given access to the nucleotides of the single-stranded template DNA. The internal base pairing in the double helix must therefore be broken and the helix unwound. Generally, the initial opening of the double helix (at the origin of replication) is performed by an initiator protein (Stenlund, 2003). DNA helicases can melt base pairs using the energy released during the process of binding, hydrolysis and release of ATP.

DNA helicase travels ahead of the replication fork, continuously opening and unwinding the DNA double helix to provide the template needed by the DNA Polymerase. With a rotational speed of up to 10,000 rotations per minute, the helicase rivals the rotational speed of jet engine turbines. When I first encountered and studied the mechanisms of DNA replication in my early undergraduate days, I was stunned by its complexity and elegance. I later came to the realization, however, that my initial conception of the sophistication of these molecular machines was a gross underestimation. The closer I inspected the nanomachinery responsible for information processing in the cell, the more I felt a sense of astonishment and marvel. You could write an entire book about each and every one of the numerous nanomachines needed for successful DNA replication. Indeed, such a book on DNA helicases and related DNA motors was recently published.

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