DNA Replication Chapter 12 Section 2

DNA Replication DNA is coped during the S phase of interphase. DNA Replication is semiconservative

Semiconservative Replication Begins with one double stranded DNA molecule. Semiconservative – Each new DNA molecule contains one strand from the original and one new strand.

Steps of DNA replication Unwinding Base pairing Joining Results in 2 Identical copies of original DNA Strand

DNA unwinding hydrogen bonds between nitrogenous bases “unzipped” by the enzyme DNA helicase at the replication fork Single stranded binding proteins hold the DNA strands apart RNA primer added to each strand of DNA

DNA Base pairing enzyme DNA polymerase adds nucleotides to the 3’ end of the new DNA strand (A T and C  G) Only adds in 5’ to 3’ Direction Results in Leading strand and lagging strand. Lagging strand broken into Okazaki fragments.

What is the 5’ and 3’ end? It is just the position on the 5 ring carbon

DNA Joining RNA Primer is removed Gaps in DNA are filled in by DNA polymerase. DNA Ligase bonds the Okazaki fragments together 2 Exact copies of original DNA!

Replication Summary 1) DNA strands pulled apart by helicase at replication fork 2) SSBs bind to keep strands apart 3) RNA primase adds RNA primer 4) DNA polymerase adds DNA nucleotides starting at primer 5’ to 3’ 5) RNA primer removed 6) Gaps filled in by DNA polymerase 7) DNA ligase joins Okazaki fragments

How does DNA get copied so quickly? Replication begins at thousands of points along a DNA molecule in eukaryotes In prokaryotes, the chromosome is circular, so replication begins at one site

How accurate is DNA replication? If a mistake is made, DNA polymerase normally fixes it. There is only about 1 error per billion nucleotide pairs. Any error in DNA replication is called a mutation and it can have serious consequences, some good and some bad.

Copy Questions to your notes! What enzyme unzips the DNA? What is added before DNA polymerase can add bases? The lagging strand is broken into ____________ fragments. Fragments are joined together by what enzyme? DNA Helicase RNA Primer Okazaki DNA Ligase

Replicate the DNA strand Original New Strand New Strand A T G C T A C G A T G C T A C G A T G C T A C G