1. DNA Replication
Chapter 12 Section 2

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

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

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

5. 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

7. 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.

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

10. 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!

12. 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

13. 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

14. 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.

15. 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

16. 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