Properties of dna

this presentation contain physical and chemical properties of dna.

1. PHYSICAL & CHEMICAL Properties of DNA

2. CONTENTS Physical properties Ultraviolet absorption Denaturation Renaturation Chemical prope rties Nucleophiles Hydrazine Hydozlyamine

3. Alkylating agents Nitrous acid Bifunctional alkylating agents E lectophiles

4. DNA absorbs uv in range of (240nm-280nm). MAX absorption at 260nm. This absorption is monitored by spectrophotometer Calculations are done by using BEER LAMBERT LAW ULTRAVIOLET ABSORBANCE A= ECl

5. E FOR DNA IS 6600L/MOL cm. Absorbance(A)=1 at 260nm is equivalent to 50ug/ml DNA. A 260 /A 280 is a measure of DNA purity. Single stranded DNA has absorbance 40% more then double stranded. Absorbance at 260nm free bases 1.60 units single strand 1.37 units double strand 1.00 units

6. When two strands of the DNA separate as single strands. Effect of various factors on DNA DENATURATION

7. Renaturation Denatured DNA may reform when Hbond forms btw complementary base pairs. Slow cooling or addition of ions may lead to renaturation . The rate limiting step in this reaction is collision of complementary DNA molecules. Once the nucleation has initiated, rest double helix coils very fastly .

8. CHEMICAL THAT REACT WITH DNA NUCLEOPHILE Electron rich reagent that can attack on + ve ly charged carbon next to nitrogen in nitrogen bases.

9. HYDRAZINE H 2 N-NH 2 It is widely used to modify DNA.

10. Hydrozylamine Stronnucleophile and powerfull mutagen. It can disrupt h bonding physically by formation of hydroxlamino group thus prevent A-T & C-G pairing.

11. ELECTROPHILES S eek an unbranched electron pair. Good site for e attack are ring nitrogen and oxygen on nitrogen bases. ALKYLATING AGENTS Ethylmethylsulphonate Ethylnitrosourea N –methyl-N’-nitro-N- nitosoguanidino

12. They are commonly use mutagen because Depending upon site of alkylation they may alter keto enol equillibrium . Bulky alkyl adduct on the base will affect H bonding. Bifunctional alkylating agents Have two reactive group Nitogen and sulphur mustard gas They form intra or inter crosslinking btw two strands of DNA

13. Nitrous acid HNO 2 REACTS WITH AMINO GROUP OF C,G OR A in an oxidative deamination rx The deamination leads to carbonyl group

14. bibliography Richard r sinden Voet and voet Cell and molecular biology genarld karp

15. Thanks…