Nucleic acids

Nucleic acids

Large biological polymers made of nucleotides

DNA

double stranded, contains deoxyribose and thymine

RNA

single stranded, contains ribose and uracil

• Nitrogenous base

• Pentose sugar

• Phosphate group

Nucleotide made up of:

Purines

Adenine, Guanine

Pyrimidines

Cytosine, Uracil (RNA), Thymine (DNA)

Pentose sugar

ribose or deoxyribose

Phosphate group

acidic, gives nucleic acids negative charge

Phosphodiester bond

Link between nucleotides: 3′–5′ phosphate linkage

Polyanion

Nucleic acids carry many negative charges due to phosphate groups

Hydrolysate

Solution obtained after acid hydrolysis of RNA contains free bases, pentoses, and phosphate

Cold water

RNA Solubility: Slightly soluble

Hot water & Diluted NaOH

RNA Solubility: Very soluble

95% ethanol & Diluted HCl

RNA Solubility: Insoluble/precipitated

Hydrolysis of RNA

Acid (H₂SO₄) + heat breaks RNA into:

• Nitrogenous bases (purines & pyrimidines)

• Pentose sugar (ribose)

• Phosphate
  

• Test for Purines

• Test for Pentose

• Test for Phosphate

Chemical Tests for Components of Nucleotides:

Test for Purines

Principle: Purines form insoluble silver–purine complexes

• Ammoniacal silver nitrate

• NH4OH

Reagents of Test for Purines:

White precipitate

Positive result of Test for Purines:

Test for Pentose

Principle: Pentoses → dehydration to furfural → reacts with Molisch reagent → purple ring

• Molisch’s reagent

• Conc. H2SO4

Reagent of Test for Pentose:

Purple-ring at interface

Positive result of Test for Pentose:

Bial’s Test

Alternate Test for Test for Pentose:

Test for Phosphate

Principle: Phosphate + ammonium molybdate → yellow precipitate of ammonium phosphomolybdate

• Hydrolysate + NH₄OH

• 10% HNO₃

• ammonium molybdate

Reagent of Test for Phosphate:

Yellow precipitate

Positive Result of Test for Phosphate:

Ammonium phosphomolybdate

Chemical name for Yellow precipitate in Test for Phosphate