CHEMICAL AND PHYSICAL PROPERTIES OF DNA Molecular Biology CHEMICAL AND PHYSICAL PROPERTIES OF DNA
UV absorption
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
SOLUBILITY and VISCOSITY
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
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
Tautomeric Conversion Amino- (NH2) imino (=NH)
Tautomeric Conversion Keto (C=O)enol (C-OH)
Base pairing of the rare forms
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
Separating the Two Strands of a DNA Double Helix
Melting curve of Streptococcus pneumoniae DNA
Relationship between DNA melting temperature and GC content
The relationship between the GC contents and densities of DNAs from various sources
Reuniting the Separated DNA Strands Temperature DNA concentration Renaturation time Hybridization: renaturation of complementary sequences between different nucleic acid molecules.