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Outcomes DNA Replication 3.4.1 Explain DNA replication in terms of unwinding the double helix and separation of the strands by helicase, followed by formation of the new complementary strands by DNA polymerase. 3.4.2 Explain the significance of complementary base pairing in the conservation of the base sequence of DNA. 3.4.3 State that DNA replication is semiconservative. IB Biology Core Topic 3.4 DNA Replication replication is a process that copies a strand of DNA to produce a new strand with the same sequence of bases. When a cell is preparing to divide it must copy all of the DNA in effect doubling the amount of DNA found in the cell. When DNA is getting ready to replicate it is in the form of chromatin and not the highly condensed chromosomes. Two things are needed for DNA replication; enzymes which include DNA helicase and a group of enzymes called DNA polymerase and free floating nucleotides. The first step in the replication of DNA involves the unwinding of the parent strand. Once the double helix unwinds the two strands need to separate. DNA The hydrogen bonds between the complementary base pairs need to be broken in order to separate the DNA strands. The enzyme DNA helicase is used to break the hydrogen bonds and unzip the DNA strand. The unzipped strands of DNA now act as templates to build the new complementary strands. Free floating nucleotides that are found inside the nucleus form complementary hydrogen bonds with the nucleotides in both of the DNA parent strands. The nucleotides are also forming covalent bonds as the sugar and phosphate backbone of one side of the DNA is forming. This forms two new strands of DNA The enzyme DNA polymerase is responsible for attaching the free floating nucleotides to the parent strands to form the replicated DNA. The result is two identical strands of DNA, each containing half of the original parent strand and they will wind back into double helices Complimentary Base Paring The complementary base pairing ensures that each of the new strands is complementary to the template used to make it which ensures exact copying and the base sequence of DNA nucleotides is conserved. Due to the fact that each nitrogen base will only fit with one other base, it ensures that the two new daughter strands are identical to each other and the parent strand from which they were made. SemiSemi-Conservative Replication DNA replication is a process that copies a strand of DNA to produce a new strand with the same sequence of bases. DNA replication is semi-conservative because each new strand produced by replication contains half of the original parent strand. In other words, half the parent strand is conserved in each of the new daughter strands. An Animation (only the first two parts for SL!) http://www.youtube.com/watch?v=oNW_ ykH3AvA&feature=related