1. The History of DNA
TSW explain how the genetic code is contained within DNA
TSW investigate the exploration of DNA structure

2. What is DNA? DNA stands for Deoxyribonucleic Acid
DNA is present in the nucleus of all eukaryotic cells
DNA controls all the chemical changes which take place in cells
The kind of cell which is formed (i.e. muscle, blood, nerve, etc) is controlled by DNA
The kind of organism which is produced (i.e. buttercup, giraffe, herring, human, etc) is controlled by DNA

3. DNA Molecule
DNA is a macromolecule (i.e. “Giant Molecule”) made up of a long chain of sub-units (monomers) called NUCLEOTIDES
Each NUCLEOTIDE has 3 main parts…
Phosphate Group (SUN)
5-Carbon Sugar (HOUSE)
Nitrogenous Base (POOL)

4. Nucleotide Structure
In DNA, the phosphate, DEOXYRIBOSE sugar, and a nitrogenous base combine to form a NUCLEOTIDE
adenine
deoxyribose
PO4

5. DNA’s Structure DNA is a double helix (*think twisted ladder)
4 Nitrogenous Bases
Adenine
Thymine
Guanine
Cytosine

6. Nitrogenous Bases Purines Pyrimidines Adenine (A) Guanine (G) A or G
Thymine (T)
Cytosine (C)
A or G
T or C

7. More DNA Structure Sugar-Phosphate backbone (sides of the ladder)
Nucleotides held together by H bonds (rungs of the ladder)

8. Discovering DNA: A Team Effort
Frederick Griffith (1928)
Question: How do bacteria make people sick?
Answer: Transformation

9. Transformation
Process in which one strain of bacteria is changed by a gene(s) from another strain of bacteria

10. Oswald Avery (1944)
Question: Which molecule is important for transformation?
Answer: DNA stores & transmits genetic info from 1 generation to the next

11. Hershey & Chase (1952) Question: Are genes made of DNA or protein?
Experiment: Which part of a bacteriophage enters the bacterium?
Answer: DNA

12. Hershey/Chase Experiment

13. Erwin Chargaff DNA base-pairing rules Adenine must pair with Thymine
Guanine must pair with Cytosine
Their amounts in a given DNA molecule will be about the same.

14. What does base-pairing look like?C G
H-bonds T A

15. Chargaff’s Rule
Remember: Bases form the rungs on the “DNA ladder” by complementary pairing

16. “Race for the Double-Helix”
Rosalind Franklin (1952): Used X-ray to determine that DNA is spiral-shaped
Watson & Crick (1953): Created 1st accurate model of DNA (double-helix), won the Nobel Prize

17. Draw the complementary strands
CAGGCCTAC
CATTGCAAG
TAAGCGATA
GCCATGAAT
*Don’t forget Chargaff’s Rule