1. CHEMICAL AND PHYSICAL PROPERTIES OF DNA
Molecular Biology
CHEMICAL AND PHYSICAL PROPERTIES OF DNA

2. UV absorption

3. DENSITY 1.7 g cm-3, a similar density to 8M CsCl
Purifications of DNA: equilibrium density gradient centrifugation
Protein floats
RNA pellets at the bottom

4. SOLUBILITY and VISCOSITY

5. Effect of Acid
Strong acid + high temperature: completely hydrolyzed to bases, riboses/deoxyrobose, and phosphate
pH 3-4 : glycosidic bonds attaching purine (A and G) bases to the ribose ring are broken

6. Effect of Alkali
High pH (> 7-8) has subtle (small) effects on DNA structure
High pH changes the tautomeric state of the bases
enolate form
enolate form
keto form
keto form
Base pairing is not stable anymore because of the change of tautomeric states of the bases, resulting in DNA denaturation

7. Tautomeric Conversion Amino- (NH2) imino (=NH)

8. Tautomeric Conversion Keto (C=O)enol (C-OH)

9. Base pairing of the rare forms

10. RNA hydrolyzes at higher pH because of 2’-OH groups in RNA
2’, 3’-cyclic phosphodiester
alkali OH
free 5’-OH
RNA is unstable at higher pH

11. Separating the Two Strands of a DNA Double Helix

12. Melting curve of Streptococcus pneumoniae DNA

13. Relationship between DNA melting temperature and GC content

14. The relationship between the GC contents and densities of DNAs from various sources

15. Reuniting the Separated DNA Strands
Temperature
DNA concentration
Renaturation time
Hybridization: renaturation of complementary sequences between different nucleic acid molecules.