DNA and RNA

DNA and RNA

1. Building nucleic acids

   • 5' to 3' direction
   • Bonding of nucleotides results in phosphate backbone with variable nitrogenous base units
   • Phosphodiester linkage
   • β-glycosidic linkage in nucleoside between pentose sugar and base

2. DNA

   • Double stranded, double helix
     • Complementary strands
   • 2 sugar-phosphate backbones run in opposite 5' - 3' directions, antiparallel
   • Sugar-phosphate backbone outside helix
   • Nitrogenous base pair on inside, hold 2 strands together
     • A pairs with T
     • C pairs with G
   • Chargaff's rule
     • A:T = 1:1 and C:G = 1:1
   • Alternative forms
     • A, B and Z
       • Conformation of DNA depends on variety of factors, B is most common
     • Linear, circular, supercoiled

3. DNA: Why a helix?

   • Angle of rotation between adjacent base pairs = 34.6°
   • Major groove = 2.2nm wide
   • Minor groove = 1.2nm wide
   • 1 turn = 10 base pairs= 3.4nm
   • Helix diameter = 2.37nm
   • Edges of bases more accessible in major grooves allowing proteins to bind to specific sequences in DNA
   • Forces that help form DNA double helix
     • Rigid phophate backbone
     • Stacking interactions: electronic interactions between planar bases
     • Hydrophobic interactions: Highly negative phosphate backbone vs non-polar bases

4. DNA key facts

   • Genetic material inherited from parents
   • Bases: A, T, G, C
   • Ladder-like molecule
   • Double stranded helix
   • Each strand is a linear polymer made of nucleotides
   • Sugar: Deoxyribose

5. RNA key facts

   • Usually single stranded
   • Sugar: ribose
   • Bases: A,G,C,U