1. DNA REPLICATION

2. DNA Replication Anchor S11.B.2.2 Objectives: You should be able to:
Explain the need for replication
Describe and model the steps of replication
Identify the work of the enzymes of replication
Distinguish leading and lagging strands
Define “semiconservative”

3. Vocabulary Replication Semi-conservative Replication fork
Leading strand
Lagging strand
Okazaki fragments
Helicase
DNA polymerase
DNA ligase

4. Why DNA?

5. DNA REPLICATION
The purpose of replication is to create two identical strands of DNA (chromosomes) prior to cell division.
If either of the two new cells being produced lack a chromosome or have too many chromosomes or have an error in the DNA, a mutation will occur.

6. DNA REPLICATION The replication of DNA is said to be semi-conservative
because one half of each newly created molecule is the original strand, and the other half is the newly synthesized strand.

7. Semi-conservative Replication

8. Origin of Replication Located by DNA polymerase
There are generally several origins on a eukaryotic chromosome because it is linear
This speeds the replication process
Circular DNA of bacteria is opened at one origin, but replicated in both directions.

9. Origins of Replication

10. Origin of Replication in Prokaryotes v. Eukaryotes

11. DNA REPLICATION DNA is unwound and “unzipped” by helicase.
Helicase breaks the hydrogen bonds between the nitrogen bases.
The point of separation (“unzipping”) of the DNA molecule is known as the replication fork.

12. Find the replication fork

13. DNA REPLICATION
DNA polymerase adds nucleotides in a 5’ to 3’ direction along both sides of the unzipped DNA strand.

14. THE LEADING STRAND
The side of the DNA molecule designated as 3’ is the template for the leading strand.
It is called leading because nucleotides can be added in a continuous motion toward the replication fork.

15. THE LAGGING STRAND
The side of the DNA molecule designated as 5’ is the template for the lagging strand.
Nucleotides cannot be added in a continuous motion because they are being added away from the replication fork.

16. THE LAGGING STRAND Nucleotides are added in small segments known as
Okazaki fragments.
Okazaki fragments are joined together by the enzyme called
DNA ligase.

18. DNA REPLICATION
Following replication, DNA polymerase “proofreads” the new strands for any mistakes.
If base pairs have been mismatched, DNA polymerase corrects the errors.

19. Replication in Action