How is DNA replicated-?

Answer 1

In a cell, DNA replication must happen before cell division can occur. DNA synthesis begins at specific locations in the genome, called "origins", where the two strands of DNA are separated. RNA primers attach to single stranded DNA and DNA polymerase extends from the primers to form new strands of DNA, adding nucleotides matched to the template strand. The unwinding of DNA and synthesis of new strands forms a replication fork. In addition to DNA polymerase, a number of enzymes are associated with the fork and assist in the initiation and continuation of DNA synthesis

by joieman04

Answer 2

The first step in DNA replication is the binding of DNA helicase, which unwinds the double helix of DNA. Single-stranded binding proteins attach to the separated strands to hold them apart. DNA gyrase, a type of topoisomerase, binds further down the strands. Gyrase breaks, twists, and rejoins the DNA strands to relieve the strain placed upon them by the unwinding of the helicase.

Replication always occurs 5' to 3'. Because of DNA's antiparallel structure, the two strands replicate in slightly different ways. The first strand, the leading strand, extends from the 3' end where the helicase first unwound the strands, to the 5' end, where the two strands are still attached. RNA primase binds to the 3' end and lays down an RNA primer of a small number of nucleotides. Once the primer is laid, DNA polymerase III (in prokaryotes) binds to the leading strand and begins the synthesis of the new strand of DNA, proceeding along 5' to 3'. Once the strand is complete, DNA polymerase I (again, in prokaryotes) replaces the RNA primer with DNA and ligase joins the gap from where the primer was.

The other strand, called the lagging strand, has an immediately apparent problem. It proceeds 5' to 3', from the origin of replication to the edge of the replication bubble - but the new strand must be synthesized from 5' to 3' as well. Therefore, the lagging strand is replicated in segments called Okazaki fragments, proceeding 5' to 3'. Each time a new fragment begins, they require an RNA primer. These primers will also be eventually replaced with DNA by DNA polymerase I and the gaps between the fragments are joined by ligase.

Answer 3

DNA replication begins with the "unzipping" of the parent molecule as the hydrogen bonds between the base pairs are broken.