1. DNA’s Discovery and Structure

2. DNA (Deoxyribonucleic Acid)

3. Important Scientists that determined DNA’s Importance
Frederick Griffith – bacterial transformation

4. Oswald Avery – DNA = key to transformation

5. Bacteriophage transformation experiment
Alfred Hershey & Martha Chase
Bacteriophage transformation experiment

6. Erwin Chargaff – base-pairing rules

7. Important Scientists in the “Race for the Double Helix”
Rosalind Franklin & Maurice Wilkins
X-ray diffraction
DNA must be a some type of spiral (helix)
DNA’s diameter is constant and stable

8. James Watson & Francis Crick
Created the first accurate model of DNA
Won the Nobel Prize

9. DNA’s Structure DNA is a double helix
DNA is made of 2 long stands of nucleotides arranged in a specific way
DNA is a double helix

10. DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group
Nitrogenous base
(A, G, C, or T)
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)

11. DNA Double Helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

12. DNA contains four nitrogen bases:
PURINES
1. Adenine (A)
2. Guanine (G)
PYRIMIDINES
3. Thymine (T)
4. Cytosine (C)
A or G
T or C

13. BASE-PAIRINGS C G
H-bonds T A

14. Chargaff’s Rule A == T C == G T == A G == C
The bases form the “rungs” on the DNA ladder by complementary pairing
A == T
C == G
T == A
G == C
Sugar-phosphate backbone

15. DNA is wrapped tightly around histones and coiled tightly to form chromosomes

16. DNA Replication A-T, G-C
DNA must be copied
The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing:
A-T, G-C
Each strand of the original DNA serves as a template for the new strand

17. DNA Replication Replication = Duplication
Happens in the S phase of Interphase
Must replicate before mitosis or meiosis I
Part of the double helix is unwound
Enzyme stitches pieces together later

18. Semi-Conservative Replication
One-half of each new molecule of DNA is old (template strand)
One-half of new molecule of DNA is new (complementary strand)

19. Steps of DNA Replication
1. DNA is unzipped by the enzyme DNA Helicase.
She does this by breaking the hydrogen bonds found between his nitrogen bases.
2. The enzyme DNA Polymerase will rebuild DNA by dropping off complementary or matching DNA nucleotides to all of his exposed bases.
3. In the end, there will be 2 DNA’s and they will be identical to each other.
*** This happens in the nucleus during S phase

20. What is a Gene? A length of DNA on a chromosome
May be in several parts
Exon – the expressed parts of the DNA sequence
Intron – the intervening, “junk DNA”, not expressed
Parts are cut, put together and then used to make RNA and proteins

21. DNA in Eukaryotes
Found in the nucleus
In the form of chromosomes

22. DNA in Prokaryotes Found in the cytoplasm because they have no nucleus
In the form of a plasmid (circular)