1. DNA: Deoxyribose Nucleic Acid The Genetic Material
Lecture #22A
Ms. Day Honors Biology

2. DNA Deoxyribose nucleic acid  type of nucleic acid
What is the other type of nucleic acid?
RNA
DNA function
to hold genetic code
Genetic code = genetic instructions to make proteins
DNA is found in nucleus of eukaryotic cells
Found in nucleoid region in prokaryotes

3. The Short History of DNA and Genetics (Part 1)
From

4. Searching for Genetic Material
Freidrich Miescher(1868):
discovered DNA
Isolated something new from the nuclei of eukaryotic cells
Later called DNA!!!

5. Searching for Genetic Material
Fredrick Griffith (1928):
Studied effects of virulent (virus-causing) bacteria vs. nonvirulent bacteria injected into mice
He used transformation:
Inserted foreign DNA and changed protein/ trait
believed that the transforming agent was an inheritance molecule

6. Non-virulent vs. Virulent Bacteria
ROUGH: harmless
SMOOTH:
kill

7. NOT HARMFUL/BENIGN
BAD/HARMFUL

8. Griffith's Transformation Experiment
Used the Pneumococcus bacteria
a virulent S strain with a Smooth coat
kills mice
a non-virulent R Rough strain
does not kill mice.
Heat destroys (kills) living cells!!!
He heated smooth (harmful) cells
So cells were DEAD!
Then he mixed them with living Rough (benign) cells and injected into mice, BUT the mouse dies.
WHY?

9. Searching for Genetic Material

10. Searching for Genetic Material
Oswald Avery, Colin MacLeod, & Maclyn McCarty (1944):
Reported that “transforming agent” in Griffith's experiment was DNA
Also used the Pneumococcus bacteria and test tubes (NOT mice)

11. So…DNA is the transforming agent!!

12. Discovering the Structure of DNA
Edwin Chargaff (1950)
Discovered a 1:1 ratio of adenine to thymine and guanine to cytosine in DNA samples from a variety of organisms.

13. Relative Proportions (%) of Bases in DNA
Chargaff's Rule (Data)
Relative Proportions (%) of Bases in DNA
ORGANISM A T G C
Human
30.9
29.4
19.9
19.8
Chicken
28.8
29.2
20.5
21.5
Grasshopper
29.3
20.7 
Sea Urchin
32.8
32.1
17.7
17.3
Wheat
27.3
27.1
22.7
22.8
Yeast
31.3
32.9
18.7
17.1
E. coli
24.7
23.6
26.0
25.7

14. Discovering the Structure of DNA
Chargaff’s Rules
A = T
C = G

15. Discovering the structure of DNA
Maurice Wilkins (1952)
Photographed DNA using x-ray crystallography
Worked with another scientists named Rosalind Franklin
Awarded the 1962 Nobel Prize for Physiology or Medicine with Watson and Crick

17.  X-rays passing through a helix diffract at angles perpendicular to helix making an "X" pattern, which favors an equal diameter "helix".

18. Discovering the structure of DNA
Photo 51
Rosalind Franklin
(1952)
Obtained sharp X-ray diffraction photographs of DNA (Photo 51)
Watson and Crick used her data  revealed its helical shape
Watson and Crick went on to win Nobel Prize (1962) for their DNA model

19. She finally gets credit 
Rosalind Franklin University of Medicine and Science, located on Green Bay Road in
North Chicago, Illinois

20. Searching for Genetic Material
Alfred Hershey & Martha Chase (1952)
Confirmed DNA IS genetic material
Used bacteriophages (viruses)
HYPOTHESIZED DNA, not protein, is the hereditary material

21. Searching for Genetic Material
Hershey and Chase Experiment Animation

22. Searching for Genetic Material Hershey and Chase Experiment

23. Discovering the structure of DNA
James Watson & Francis Crick (1953)
Discovered double helix structure
Solved the three-dimensional structure of the DNA molecule

24. Ms. Gaynor Honors Biology
DNA’s Structure
Lecture #22B
Ms. Gaynor Honors Biology

25. DNA and Its Structure (Part 2)
From 1953

26. Recall… DNA and RNA are nucleic acids
An important macromolecule in organisms that stores and carries genetic information

27. What is the Double Helix?
Shape of DNA
Looks like a twisted ladder
2 coils are twisted around each other
Double means 2
Helix means coil

28. 1 “link” or monomer in a DNA chain
The Structure of DNA
Made out of nucleotides
MONOMERS of nucleic acids
Includes:
phosphate group (PO4-3)
nitrogenous base and
5-carbon pentose sugar
1 “link” or monomer in a DNA chain

29. DNA has a overall negative charge b/c of the PO4-3 (phosphate group)
2 Polynucleotides
MANY nucleotides (“links”) bonded together
DNA has a overall negative charge b/c of the PO4-3 (phosphate group)

30. The Structure of DNA Backbone Backbone = alternating PO4-3 & sugar
Held together by COVALENT bonds (strong)
Inside of DNA molecule = nitrogen base pairs
Held together by HYDROGEN bonds (weaker)
Backbone

31. The covalent that holds together the backbone
Phosphodiester Bond
The covalent that holds together the backbone
Found between PO4-3 & deoxyribose sugar of 2 DIFFERENT nucleotides
STRONG!!!

32. DNA is antiparallel
Antiparallel means that the 1st strand runs in a 5’ 3’ direction and the 2nd 3’ 5’ direction
THEY RUN IN OPPOSITE or ANTIPARALLEL DIRECTIONS
P end is 5’ end (think: “fa” sound)
-OH on deoxyribose sugar is 3’ end
5’ and 3’ refers to the carbon # on the pentose sugar that P or OH is attached to

33. DNA in Cells 2 broad categories of cells
1. Eukaryotic cells: have nucleus with DNA
DNA is contained in structure called a chromosome
Chromosomes are a LINEAR (line) shape with ENDS called telomeres (protective “caps”)
2. Prokaryotic cells: no nucleus (nucleoid region instead) which contains DNA
DNA is a CIRCULAR shaped chromosome without ENDS (no telomeres)

34. DNA Bonding Purines (small word, big base) Pyrimidines
Adenine
Guanine
Pyrimidines
(big word, small base)
Cytosine
Thymine
Chargaff’s rules
A=T, C=G
Hydrogen Bonds attractions between the stacked pairs; WEAK bonds

35. Why Does a Purine Always Bind with A Pyrimidine?

36. DNA Double Helix LET’S PRACTICE…
Watson & Crick said that…
strands are complementary
nucleotides line up on template according to base pair rules (Chargaff’s rules)
A to T and C to G
LET’S PRACTICE…
Template: ’ AATCGCTATAC3’
Complementary strand: 3’ TTAGCGATATG5’