1. DNA Replication
Ask why, when, and where they think replication occurs? Ask them to recall when copies are needed?

2. Facts: DNA replicates before a cell divides
Occurs during the S or synthesis phase of mitosis
Replication creates identical copies of DNA strands
Takes place in the nucleus

3. DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone 3

4. Replication: Begins at Origin of Replication
Two strands open forming a Replication Forks (Y-shaped region)
New strands grow at the forks
Replication
Fork
Parental DNA Molecule 3’ 5’

5. Enzymes
The Enzyme, Helicase, unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds
DNA polymerase adds nucleotides complimentary to the parental strand

7. Mutations
What do you think a mutation is?

8. Proofreading Replication occurs at multiple sites along the DNA
DNA polymerase is very accurate
However mutations do occur
Proofreading occurs continuously by DNA polymerase

9. More practice Write the complimentary strand:
T A C G G A C T A A C G C

10. More practice Write the complimentary strand:
T A C G G A C T A A C G C
A T G C C T G A T T G C G

11. Review:
If there is 20% Thymine bases on a DNA strand what are the percentages of the other three bases?

12. Answer: 20% Thymine = 20% Adenine 20% + 20% = 40 % 100% - 40% = 60%
60% / 2 = 30%
30% Cytosine and 30% Guanine

13. Review When and where does DNA replication occur?
What is the relationship between adenine and thymine called?
What are the two enzymes involved in DNA replication?
DNA replication occurs during the S or synthesis phase of cells, during mitosis and meiosis, in the nucleus
A and T are complimentary base pairs
Helicase, breaks hydrogen bonds and DNA polymerase, adds nucleotides and proofreads DNA

14. Activity
In pairs you are going to create your own DNA models.

15. Pieces Sugar - Black pentagon Phosphate - White tube
Nitrogenous bases -
Adenine - Orange (5)
Guanine - Yellow (4)
Cytosine - Blue (4)
Thymine - Green (5)
Hydrogen bonds - White rods

16. Procedure Create 18 nucleotides Put together a 9 rung ladder of DNA
Be sure to have correct base pairing
After having a complete DNA molecule create 18 more nucleotides

17. DNA replication Begin to “unzip” DNA molecule from one end
Add complimentary nucleotides to create two DNA molecules