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A helicase is an enzyme that plays a crucial role in the DNA replication and repair processes. Its primary function is to unwind the double-stranded DNA molecule by breaking the hydrogen bonds between the complementary base pairs, allowing the DNA strands to separate.
The replication fork is a structure that forms within the long helical DNA during DNA replication. It is produced by enzymes called helicases that break the hydrogen bonds that hold the DNA strands together in a helix. The resulting structure has two branching "prongs", each one made up of a single strand of DNA.
DNA gyrase, or simply gyrase, is an enzyme within the class of topoisomerase and is a subclass of Type II topoisomerases [1] that reduces topological strain in an ATP dependent manner while double-stranded DNA is being unwound by elongating RNA-polymerase [2] or by helicase in front of the progressing replication fork.
An enzyme called DNA ligase connects the gap in the backbone by forming a phosphodiester bond between each gap that separates the Okazaki fragments. The structural and chemical aspects of this process, generally referred to as 'nick translation', exceed the scope of this article.
The enzyme is integrated into thylakoid membrane; the CF 1-part sticks into stroma, where dark reactions of photosynthesis (also called the light-independent reactions or the Calvin cycle) and ATP synthesis take place. The overall structure and the catalytic mechanism of the chloroplast ATP synthase are almost the same as those of the bacterial ...
In both prokaryotes and eukaryotes, replication is accomplished by unwinding the DNA by an enzyme called the DNA helicase. New strands are created by enzymes called DNA polymerases. Both of these follow a similar pattern, called semi-conservative replication, in which individual strands of DNA are produced in different directions, which makes a ...
The steric model hypothesizes that the helicase encircles dsDNA and, after local melting of the duplex DNA at the origin, translocates away from the origin, dragging a rigid proteinaceous "wedge" (either part of the helicase itself or another associated protein) that separates the DNA strands. [32]
Reverse gyrase, which occurs in thermophilic archaea, comprises a type IA topo coupled to a helicase, and is the only known enzyme that can introduce positive supercoils into DNA. [24] The gene encoding reverse gyrase is also found in some groups of thermophilic bacteria, where it was likely transferred by horizontal gene transfer from Archaea.