DNA Replication IB Topic 3.4 Campbell Chapter 16

Replication – How DNA copies itself  In order that a copy of each chromosome can pass into the daughter cells at cell division, the DNA of the chromosomes must first be copied (replicated) Why is this important? When does this happen?  DNA carries the genetic message Replication must be extremely accurate Why?

DNA Replication is Semi-Conservative  At the end of DNA replication, we have two new strands of DNA Double helix shape  Both (new) DNA molecules are composed of an original strand and a newly synthesized strand Semi-conservative

Steps of Replication  The DNA double helix unwinds  The hydrogen bonds holding the strands together are broken  The enzyme helicase (and some others) is involved in these steps and holds the strands apart while replication occurs

Steps of Replication  Both strands act as templates  New nucleotides (complementary base pairing!) line up opposite the bases of the exposed strand A = T & C = G  The sequence on one DNA strand determines the sequence of the other strand They’re complementary

Steps of Replication  Hydrogen bonds hold together the complementary bases  The sugar/phosphate groups of adjacent nucleotides of the new strand condense together Reaction is catalyzed by the enzyme DNA polymerase

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