1. Do Now!!  Why must DNA be replicated?
Where do you think replication takes place?
Are mistakes ever made while replicating DNA?

2. DNA Replication!

3. Objectives
Explain what replication is and why it must occur in our bodies.
List the different enzymes involved in each step of replication and what they do.
Compare and contrast leading vs. lagging strands.

4. Replication video!

5. Semiconservative Replication
Parental strands of DNA separate
Each strand serves as template
DNA molecules produced have one strand of parental DNA (old) and one daughter strand (new):
“semi”- half
“conserve”- save

6. Enzymes involved Helicase- unzips the DNA strand
Primase- adds RNA Primer (tells the next enzyme where to begin!)
DNA polymerase- adds new nucleotides
DNA ligase- links together fragments

7. Steps to DNA Replication 1. Unwinding
DNA helicase (enzyme) unwinds and unzips the DNA – breaking the hydrogen bonds between the strands
Single-stranded binding proteins (SSB)- go to DNA strand to keep them separated during replication.
RNA primase adds a short segment of RNA, called an RNA primer, on each DNA strand.

8. 1. Unwinding (cont.) DNA unwinds at different spots (Origins)
At the replication fork, an enzyme (Helicase) breaks the
hydrogen bonds between the bases

9. Steps to DNA Replication (cont.) 2. Base Pairing
DNA polymerase (enzyme) adds complementary nucleotides to parent DNA strand
Only adds in the 5’ to 3’ direction!!!!!

10. 2. Base Pairing (cont.)
Two daughter strands of DNA are made differently
Leading Strand- Elongated as the DNA unwinds.
Built continuously without breaks
Lagging Strand- Elongates AWAY from replication fork.
Built discontinuously
makes several small fragments of DNA called Okazaki Fragments

11. Okazaki fragments

12. Steps to DNA Replication (cont.) 3. Joining
DNA Polymerase removes RNA Primer and fills its place with DNA nucleotides
DNA ligase links the Okazaki Fragments.

13. DNA Replication

14. Mistakes in DNA DNA replication takes a lot of energy
During replication, mistakes are made (mutations)
Enzymes “proof read” and repair the mistakes:
Ex: DNA polymerase, exonuclease

15. Eukaryotes vs. Prokaryotes
Eukaryotic DNA unwinds in multiple areas as DNA is replicated.
In prokaryotes, the circular DNA strand is opened at one origin of replication.

16. Do Now
Label the DNA Replication Diagram 7 1 6 2 5 3 4

17. Flash Tutorial *