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Summary of DNA Replication
DNA replication begins when the protein helicase locates the origin of replication and binds to it via electric forces. Helicase then proceeds to unwind the double helix of the DNA by breaking the hydrogen bonds between the nitrogenous bases. DNA gyrase, a topoisomerase, then binds to the double helix and induces negative supercoils, which decreases the stress that is involved with the unwinding process. Another enzyme called primase (which is an RNA polymerase) then forms RNA primers, which are short sequences of nucleotides that signal DNA polymerase to begin the synthesis of the new daughter strands. DNA polymerase lays down the free nucleotides found in the surrounding environment and catalyzes the formation of phosphodiester bonds. DNA polymerase has a proof-reading mechanism that gives it the ability to fix any mismatches that are made during the replication process. Since DNA polymerase can only read the parent strand in the 3' to 5' direction and synthesize the strand in the 5' to 3' direction, only the leading stand is synthesized continuously. The other daughter stand, known as the lagging strand, must be synthesized in a piece-by-piece, discontinuous fashion. Each one of these pieces is known as an Okazaki fragment. Once all the fragments are synthesized, a protein called DNA ligase connects the fragments by catalyzing the formation of phosphodiester bonds.
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