1. Griffith (1928 ) Streptococcus pneumoniae ( 폐렴균 ) virulent (S) smooth colonies : with capsules Heat-killed virulent colonies could transform avirulent colonies to virulent ones avirulent (R) rough colonies without capsules Chapter 2. The molecular nature of genes Hershey-Chase (1940’s) ; bacteriophage ; P 32 (label DNA), S 35 (label protein)

2. Physical-chemical analysis Physical-chemical analysis has often used: 1.Ultracentrifugation Used to estimate size of material 2.Electrophoresis Indicated high charge-to-mass ratio 3.Ultraviolet Absorption Spectrophotometry ( 흡광기술 ) Absorbance of UV light matched that of DNA 4.Elementary Chemical Analysis Nitrogen-to-phosphorus ratio of 1.67, not found in protein Avery (1944) ; treated the transforming virulent extract with protease, RNase, or DNase

3. Contributors to deciphering DNA structure 1. Fundamental chemical structure of DNA and RNA 2. Chargaff ’s rule - A similar to T; G similar to A - A+G similar to T+A 3. x-ray diffraction picture

4. Double helix Purine and pyrimidine basesSugar ; ribose and deoxyriboseGlycosidic bond 5  3’ direction Anti-parallel double helixMajor and minor grooveA-T and G-C base pairRight-handedPitch and width10.5 bp/turn

5. Composition of nucleotide 2. sugar - ribose -2’-deoxyribose - glycosidic bond with base 3. phosphate 1. bases - Phosphodiester bond - adenine, guanine, cytosine, thymine - uracil

6. Types of DNA Structures B-form ; in high humidity A-form ; Lower humidity to about 75% –Plane of base pairs in A-form is no longer perpendicular to the helical axis –A-form seen when hybridize one DNA with one RNA strand in solution Z-form ; left-handed - Some genes require Z-DNA for activation - DNA containing strands of alternating purines and pyrimidines -GCGCGCGC- -CGCGCGCG-

7. Hyperchromic shift temperature Absorbamce A260 Tm

8. C-value paradox DNA content per haploid cell speciesBase pairslength E. coli4.64 x 10 6 1.6 mm H. sapiens3.2 x 10 9 1.1 m L. Longiflorum ( 백합 ) 3 x 10 11 100 m There is a trend that the more evolved a species the more complex the genome. However, the concept above can not be generalized.

9. Why DNA is the genetic material not RNA? 1.Chemical stability (-OH is more reactive)

10. Why does DNA have thymine whereas RNA have uracil ? 1. Protected from nucleases by methylation