1. August 11, 2015 Bell Work: Objective: The student will be able to…
What are the four nitrogen bases found in DNA?
Objective:
The student will be able to…
Build a model of DNA using puzzle pieces and class notes.
Describe DNA replication by taking notes and using a model.

2. Today in History
2000 Pat Buchanan won the Reform Party presidential nomination.
2006 The Transportation Security Administration banned all liquids, gels and aerosols from passenger cabins on airliners one day after a thwarted terrorist attack.

3. DNA Model
Build a model and answer the questions on the worksheet.

4. DNA Replication

5. DNA Replication
The process of making a copy of DNA is called DNA replication
Occurs during the S phase of the cell cycle

6. DNA Replication Step 1 The double helix unwinds using DNA helicases
DNA helicases break the hydrogen bonds that link the complimentary nitrogen bases between the two strands.
Once separated additional proteins attach and keep the strands apart (preventing them from assuming their double-helical shape)

7. DNA Replication Step 1 Step 2
Replication forks: the area where the double helix separates
Step 2
Enzymes known as DNA polymerases move along each of the DNA strands
Add nucleotides to the exposed nitrogen bases forming two new strands of DNA

8. DNA Replication Step 3 End product
The process continues until all of the DNA has been copied and the polymerases are signaled to detach
End product
Two identical DNA molecules each composed of one new and one original strand

9. Checking for Errors Errors do occur during DNA replication
DNA polymerases have a “proofreading” role
This means that DNA polymerases can back track if they have mismatched nucleotides
Reduces errors to about 1 per billion nucleotides

10. Rate of Replication
DNA Replication does not begin on one end and end at the other
Prokaryotes: two replication forks start at the same point and move away from each other until they have completely replicated the circular strand of DNA.

11. Rate of Replication
In eukaryotic cells each chromosome is composed of a single long strand of DNA.
There are multiple replication forks on each strand
Each chromosomes is replicated in approximately 100 sections that are 100,000 sections long.

12. DNA Worksheet

13. Crash Course Biology

14. Ticket Out
Explain why DNA replication is semi- conservative.