1. Journal 5-3: Modeling DNA

2. Nucleotides Monomers of DNA Each Nucleotide has 3 parts
Phosphate group
Sugar (Deoxyribose)
Nitrogenous Base

3. Nucleotides (cont) Every nucleotide has a phosphate and a sugar
Nitrogenous Bases vary
Purines
Adenine
Guanine
Pyrimidines
Cytosine
Thymine

4. Nucleotides (cont) CUT the Py
Purines - nucleotides with a 2-ring nitrogenous base
Adenine and Guanine
Pyrimidines - nucleotides with a 1-ring nitrogenous base
Thymine and Cytosine
CUT the Py

6. Nucleotide Bonding
Dehydration synthesis reaction connects the phosphate group from one nucleotide to the sugar group from another nucleotide.

7. Base Pairing
2 bonds
Nitrogenous bases connect together with hydrogen bonds
3 bonds

8. DNA Structure (Watson/Crick/Franklin)

9. DNA Replication Why does a cell replicate it’s DNA?
To make an identical copy!
When would a cell need to do that?
When it is dividing, so…
To make new cells

10. DNA Replication
Step 1: Helicase binds to the DNA and unwinds the 2 strands (exposing nitrogenous bases)
What kinds of bonds does helicase break?
Helicase

11. DNA Replication
Step 2: DNA Polymerase adds complementary nucleotides to the exposed bases on the original strand
This forms a NEW strand attached to the OLD one
What kinds of bonds are being formed?
Helicase
DNA
Polymerase
DNA
Polymerase

12. DNA Replication
Step 3: New DNA molecules wind back up to form a double helix
Why do we say DNA replication is “Semi- conservative?”
There are now two DNA molecules, each containing one OLD strand and one NEW strand
Helicase
DNA
Polymerase
DNA
Polymerase

13. DNA Replication video