Se ha denunciado esta presentación.
Se está descargando tu SlideShare. ×

Structure of dna , dna polymorphism

Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Próximo SlideShare
Dna structures
Dna structures
Cargando en…3
×

Eche un vistazo a continuación

1 de 23 Anuncio

Más Contenido Relacionado

Presentaciones para usted (20)

Similares a Structure of dna , dna polymorphism (20)

Anuncio

Más reciente (20)

Anuncio

Structure of dna , dna polymorphism

  1. 1. PRESENTED BY: Mousami Jaria St. George College of Management and Science MSc Microbiology Semester 2 STRUCTURE OF DNA, DNA POLYMORPHISM [A, B, Z DNA]
  2. 2. INTRODUCTION  DNA is composed of two polynucleotide chains twisted around each other in the form of double helix.  The double helix looks superficially same because of the complimentary nature of the two DNA strands.  The nucleotide consists of phosphate joined to a sugar known as 2’deoxyribose to which a base is attached.
  3. 3.  The sugar is called 2’deoxyribose because there is no hydroxyl at position 2’.  The sugar and base alone are called nucleoside. Adding a phosphate to a nucleoside creates a nucleotide.  Nucleotides are joined to each other in polynucleotide chains through 3’hydroxyl of 2’deoxyribose of one nucleotide and the phosphate attached to 5’hydroxyl of another nucleotide.  This is phophodiester linkage in which the phosphoryl group between two nucleotides has one sugar esterified.
  4. 4.  The phosphodiester linkages impart an inherent polarity to DNA chain. This polarity is defined by the asymmetry of the nucleotides and the way they are joined.  EACH BASE HAS ITS PREFERRED TAUTOMERIC FORM:  The bases in DNA are flat heterocyclic rings consisting of carbon and nitrogen atoms.  They fall into 2 classes purines and pyrimidines i.e adenine, guanine, cytosine, thymine .
  5. 5.  Each of the bases exist in two alternative tautomeric state states which are in equillibrium with each other.  THE TWO STRANDS OF THE DOUBLE HELIX ARE WOUND AROUND EACH OTHER IN AN ANTIPARALLEL ORIENTATION:  The two chains have the same helical geometry but have opposite 5’ to 3’ orientation.  Adenine in one chain pair with thymine of other chain likewise guanine pairing with cytosine.
  6. 6.  THE TWO CHAINS OF DOUBLE HELIX HAVE COMPLEMENTARY SEQUENCE:  Pairing between adenine and thymine and between guanine and cytosine reults in complementary relationship between the base sequence on to interwined chains and gives DNA itself encoding character.  THE DOUBLE HELIX IS STABILIZED BY BASE PAIRING AND BASE STACKING:  The hydrogen bonds between contribute to thermodynamic stability and specificity of base pairing.
  7. 7.  Base stacking also contributes to the stability by hydrophobic effect.  The hydrophobic surfaces are buried by base stacking thus minimising the exposure of base surfaces to water molecules and hence lowering the free energy.  BASE CAN FLIP OUT FROM DOUBLE HELIX:  Individual bases can protrude from double helix by phenomenon called base flipping.  Certain enzymes that remove damaged bases do so with the base in an extrahelical configuration in which it is flipped out enabling the base to sit
  8. 8. in catalytic cavity of the enzyme.  THE DOUBLE HELIX HAS MAJOR AND MINOR GROOVES:  The narrow angle between the sugars on one edge of the base pair generates minor groove and large angle on the other hand generates major groove.  The major groove is rich in chemical information.
  9. 9.  DNA STRANDS CAN SEPARATE (DENATURE) AND REASSOCIATE:  The complementary strands of double helix can be made to come apart by process called denaturation. But this is reversible.  However when the heated solutions of denatured dna cools single strands often meet there complementary strands.  The capacity to renature denatured DNA molecules permits artificial hybrid dna molecules to be formed.  The ability to form hybrids between two single stranded nucleic acids is called hybridization
  10. 10.  THE DOUBLE HELIX EXISTS IN MULTIPLE CONFORMATIONS:  X-ray diffractions revealed thet there are A, B, Z forms of DNA.  The B form of DNA represents the ideal structure and forms right handed helix.  The Z DNA forms a left handed helix .
  11. 11. DNA POLYMORPHISM • Refined resolution of DNA structure ,based on X-ray crystallography of short synthetic pieces of DNA has shown that there is considerable variance of helical structure of DNA. o There are three families of DNA helices: o A- DNA : Which can readily form within certain stretches of purines (eg: GAGGGA)
  12. 12.  B DNA: Which is favoured by mixed sequences( although the exact conformation depends on the particular nucleotide sequence)  Z-DNA: Which is favoured by alternating pyrimidine –purine steps (EG: CGCGCG).  The A and B DNA families are right handed helices, while Z DNA family has a left handed orientation of helix.  The different conformations of DNA helix have important biological functions.
  13. 13. A-DNA:  A-DNA is one of the possible double helical structure which DNA can adopt along with other two biologically active helix structure(B-DNA, Z-DNA).  Right handed double helix  Short and thick compared to B-DNA.  Occur only in dehydrated sample of DNA, like those used in crystallography experiments.
  14. 14.  A-DNA was originally identified by X-ray diffraction analysis of DNA fibres at 75%relative humidity.  The grooves are not deep as in B-DNA  Bases are more tilted.  Base pair turn is 11.  Rise per base pair is 2.3 angstorm.
  15. 15. B-DNA  Discovered by Watson and Crick .  Most common form of DNA.  DNA molecule consists of 2 helical polynucleotide chains coiled around common axis  Two helices are coiled in such a way so as to produce 2 interchain spacing or groove.  Major/wide groove, Minor/ narrow groove.  .These grooves provides surface with which proteins ,chemicals, drugs interact.
  16. 16. B-DNA
  17. 17. Z-DNA  Discovered by Rich, Nordheim and Wang in 1984.  One of the many possible DNA double helix structure.  Left handed double helix structure in zig zag manner so termed as Z-DNA  Has anti parallel strand ass in B-DNA.  Long and thin in comparison to B-DNA.  Adjacent sugar have alternating orientation.
  18. 18.  In Z-DNA : a. purines: syn conformation (bases and sugar are near and on same side).  b. pyrimidines : anti (bases and sugar are distant , on opposite sides.)  Only one deep helical groove.  12 base pairs per turn with axial rise 3.8 angstorm. & angle twist of 60 degree
  19. 19. COMPARISON TABLE
  20. 20. THANK YOU

×