1. DNA
Structure
Chapter 8

2.
Be ready to write down 3 things you remember from the video!

3. DNA Stands for… DNA: Deoxyribonucleic acid
Very large biomolecule made up of nucleotides
Called the “blueprints of life” because it contains genetic information for the construction of proteins.

4. Floats freely in the cytoplasm of prokaryotes
Protected in the nucleus of eukaryotes

5. Nucleotide: DNA subunit (monomer) made up of 3 parts
Deoxyribose sugar
Phosphate group
Nitrogenous base

6. DNA Structure
Made of 2 nucleotide chains that wrap around each other to form a double helix (looks like a spiral staircase)
The sides: Alternating Sugar, phosphate, sugar, phosphate
The middle: Nitrogen bases paired together.

7. Scientists Involved in Discovery of DNA
James Watson & Francis Crick
developed double helix model of DNA
other scientists working on finding the structure:
Rosalind Franklin
Maurice Wilkins
Linus Pauling
Franklin
Wilkins
Pauling
Watson & Crick’s model was inspired by 3 recent discoveries:
Chargaff’s rules
Pauling’s alpha helical structure of a protein
X-ray crystallography data from Franklin & Wilkins

8. 1953 article in “Nature”
Watson and Crick
Watson
Crick

9. Nitrogenous Bases
There are 2 groups of nitrogenous bases: purines and pyrimidines
Purines: Made up of two rings of carbon and nitrogen
Adenine (A), Guanine (G)

10. Pyrimidines: Bases that have one ring of carbon and nitrogen
Thymine (T), Cytosine (C)

11. Identifying the structure…
Purine + purine: too wide
Pyrimidine + pyrimidine: too narrow
Purine + pyrimidine: width consistent with X-ray data

12. pair with Pyrimidine (C, T)
Conclusion:
Purine (A, G)
pair with Pyrimidine (C, T)
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)

13. Chargaff’s Base Pairing Rules
DNA composition: “Chargaff’s rules”
varies from species to species
all 4 bases not in equal quantity
bases present in characteristic ratio
humans:
A = 30.9%
T = 29.4%
G = 19.9%
C = 19.8%
1947
That’s interesting! What do you notice?

14. A pairs with T “Always Together” G pairs with C “Get Closer”
Chargaff’s Base Pairing Rules:
A pairs with T
“Always Together”
G pairs with C
“Get Closer”

15. Summary Summarize what we just talked about by:
Come up with 3 alternate titles for our notes
OR Drawing a picture to remember base pairing
OR Writing about how DNA structure is like a staircase