1. Molecular Basis Of Inheritance
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 repeated Griffith’s 1928 experiment with modifications designed to discover the “transforming factor”
Extracts from heat-killed cells were digested with hydrolytic enzymes specific for different classes of macro molecules:
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 classes of macromolecules: 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. Forms of the Double Helix
0.8 nm
Major
groove
Minor
A T
T A
G C
C G
G C
T A
0.34 nm
3.9 nm
B DNA
Z DNA
0.26 nm
2.8 nm
Minor
groove
Major
A T
T A
G C
C G
C G
T A
A T
G C
T A
G C
1.2 nm
A DNA
+34.6o Rotation/Bp
10.4 Bp/turn
+34.7o Rotation/Bp
11 Bp/turn
-30.0o Rotation/Bp
12 Bp/turn

17. Supercoiling Opened negatively supercoiled DNA
Open circle DNA with no supercoiling
Negatively (twisting to the left) supercoiled DNA
Opening negatively supercoiled DNA may contribute to strand separation

18. Distribution Of Negative Charge Prevents DNA Annealing
H2N N HN O- OH
CH3 H P O -O
CH2 OH O-
NH2 N NH

19. Salts Allow DNA AnnealingH P
CH2
H2N N HN O- OH
CH3 H P O -O
CH2 OH O-
NH2 N NH
NaCl
NaCl
Cl-
Na+
Cat ions can cancel out the negative charge carried on the sugar phosphate backbone.

20. Salts Allow DNA AnnealingH P
CH2
H2N N HN O- OH
CH3 H P O -O
CH2 OH O-
NH2 N NH
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+

21. Salts Allow DNA AnnealingH P O -O
CH2 OH O-
NH2 N NH
Na+
Na+ O H P
CH2
H2N N HN O- OH
CH3

22. Base Stacking 3’ 5’AA3’ 3’UU5’ O N H H Adenine O Uracil N Adenine

23. Base Stacking 3’ 5’AU3’ 3’UA5’ O N H H Adenine O Uracil N Adenine

24. AZT 3’-Azido-3’-deoxythymidine
CH2
Deoxy
ribose H OH
CH3 N NH
Thymine

25. The
End