Structure of DNA bio-tech

Structure of DNA 

• WATOSON AND CRICK first describe the structure of the DNA double helix by using X-rays diffraction.
• nucleotide of DNA  consist ~Deoxy Ribose                                                                                                                                          ➕                                                                                                                                   (A/T/G/C) Nitrogenous base                                                                                                                            ➕                                                                                                                                           Phosphoric acid                          
• Double helix  of DNA consist of tow strand. Each strand consist chain of nucleotide.
• Two strand are antiprallel
• purine pair with pyrimidines 
• A=T&G☰C,

Types of DNA ;

• There is three typs of DNA- B-DNA,Z-DNA  and A-DNA ,

1. B-DNA; 

 B-DNA has following major featurs-

• strands are wrapped in right handed helix.
• strands are antiparallel .
• strands interact by hydrogen band between complementary  base pair.
• A≒T&G☰C,
• B-DNA is most common DNA conformation in vivo.
• minor groove is narrow 
• base pair nearly perpendicular to helix axis 
• B-DNA is more stable then any other DNA 
• the overall charge on B-DNA  is negative beacuse of the phasphoric acid 

      2.Z-DNA;

• Z-DNA is a left handed double helical structure with tow antiparallel strand .
• Z-DNA is thinner then B-DNA 
• there is only one deep , narrow groove equivalent to the miner groove in B-DNA 
• no major groove exits

comparisons of different form of DNA

Geometry attribute	A-form	B-form	Z-form
Helix sense	Right handed	Right handed	Left handed
Base pair/turn	10.7	10.4	12
Rise /bp along axis	2.3  Å	3.32 Å	3.8 Å
Ritch	24.6	33.2	45.6
Diameter	23	20	18
Major groove	Narrow and deep	Wide and deep	Flat
Minor groove	Wide and shallow	Narrow and deep	Narrow and deep

 Stability of the dsDNA helix ;

• the helical structure of dsDNA  is stabilized by non-covalent interaction.
• these interaction include stocking interaction between adjacent bases and hydrogen bonding between complementary strands 
• the core of the helix consist of bases pairs which stock together through stocking interaction. 
• stocking interaction include hydrophobic interaction and vander walls interaction between the bases pair, that contribute significantly to overall stability