1. DNA: Prince of the Chemicals
Timothy G. Standish, Ph. D.

2. Transformation Of Bacteria Two Strains Of Streptococcus
Rough Strain
(Harmless)
Capsules
Smooth Strain
(Virulent)

3. Transformation Of Bacteria The Griffith Experiment
OUCH!
+ Control
- Control
- Control
Experimental

4. Avery, MacLeod and McCarty
1944 Avery, MacLeod and McCarty decided to repeat Griffith’s 1928 experiment and try to discover the “transforming factor”
They did this by using extracts from the heat- killed cells and digesting specific classes of molecules with enzymes
Transformation?
Enzyme
Lippase
Yes
Protease
Yes
Saccharase
Yes
Nuclease No

5. The Hershey-Chase Experiment
The Hershey-Chase experiment showed definitively that DNA is the genetic material
Hershey and Chase took advantage of the fact that T2 phage is made of only two things: Protein and DNA H OH P O HO
NH2
Nucleotides contain phosphorous, thus DNA contains phosphorous, but not sulfur. H OH O
H2N C
CH2 SH
CH3 S
Some amino acids contain sulfur, thus proteins contain sulfur, but not phosphorous.
Cysteine
Methionine

6. Using S35 Did protein enter the bacteria?
T2 grown in S35 containing media incorporate S35 into their proteins
Bacteria grown in normal non-radioactive media
T2 attach to bacteria and inject genetic material
When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet
Mix-O-Matic
The supernatant is radioactive, but the pellet is not.
Blending causes phage protein coat to fall off
Did protein enter the bacteria?
Is protein the genetic material?

7. Using P32 Did DNA enter the bacteria? Is DNA the genetic material?
T2 grown in P32 containing media incorporate P32 into their DNA
Bacteria grown in normal non-radioactive media
T2 attach to bacteria and inject genetic material
When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet
Mix-O-Matic
The pellet is radioactive, but the supernatant is not.
Blending causes phage protein coat to fall off
Did DNA enter the bacteria?
Is DNA the genetic material?

8. A Nucleotide Adenosine Mono Phosphate (AMP)OH HO
Phosphate
NH2 N
Base - H+ OH O
CH2
Sugar H 2’ 3’ 4’ 5’ 1’
Nucleotide
Nucleoside OH

9. Purines Pyrimidines Uracil CH3 N O NH Thymine N Adenine NH2 NH2 O N NH
(RNA)
CH3 N O NH
Thymine
(DNA) N
Adenine
NH2
NH2 O N NH
Guanine N O
NH2
Cytosine

10. Base Pairing Guanine And CytosineH O N
Guanine - N O H
Cytosine + + - - +

11. Base Pairing Adenine And Thymine- +
Adenine
CH3 N O H + -
Thymine

12. Base Pairing Adenine And CytosineH
Cytosine - + N H - +
Adenine

13. Base Pairing Guanine And Thymine
CH3 N O H + -
Thymine H O N
Guanine + -

14. D N A B A S E S SUGAR-PHOSPHATE BACKBONE H2O H2O H P O HO CH2 OH NH2 N

15. The Watson - Crick Model Of DNA
T A
G C
C G
G C
T A
3.4 nm
1 nm
Minor
groove
Major
groove
0.34 nm

16. Large Linear Chromosomes Have Many Origins Of Replication3’ 5’ 5’ 3’ 5’ 3’ 3’ 5’

17. Extension - The Replication Fork5’ 3’
Primase - Makes RNA primers
Single-strand binding proteins - Prevent DNA from re-annealing
Lagging Strand 3’ 5’ 5’ 3’
Okazaki fragment
RNA Primers
DNA Polymerase
Helicase - Melts DNA
Leading Strand 5’

18. Extension - Okazaki Fragments
DNA
Pol. 3’ 5’
RNA Primer
Okazaki Fragment
DNA Polymerase has 5’ to 3’ exonuclease activity. When it sees an RNA/DNA hybrid, it chops out the RNA and some DNA in the 5’ to 3’ direction.
DNA
Pol. 3’ 5’
RNA Primer
RNA and DNA Fragments
DNA Polymerase falls off leaving a nick. 3’ 5’
RNA Primer
Ligase
Nick
The nick is removed when DNA ligase joins (ligates) the DNA fragments.

19. The
End