Nucleic Acids in Chemistry and Biology

414 Chapter 10

α α

α

ADP

+Pi

ADP

+Pi

Empty

γ

F1-ATPase

NDP

+Pi

NDP

+Pi

NTP

NTP

Empty

Empty

Helicase

DNA

a

b

Figure 10.19 The structure and function of DNA helicases. (a) The T7 gene four-ring helicase, which is a
homohexamer with three non-equivalent states (PDB: 1EOK). (b) The winding mechanism involves
the DNA visiting different sites around the ring (right), which changes affinity for the nucleic acid as
it binds and hydrolyses nucleotide triphosphate then releases the nucleoside diphosphate and
inorganic phosphate. Because of the helical symmetry of the DNA, it translates during the cycle.
The mechanism is analogous to the rotatory process of the F1-ATPase (left)

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