Más contenido relacionado


Más de Dr. Kaushik Kumar Panigrahi(20)


Presentation on DNA structure and Chemical Compositions

  1. Prepared by – Santosh Kumar Das (6c/15) 2nd Year B.Sc (Ag) Submitted To- Dr. Kaushik Kumar Panigrahi Asst. Professor Plant Breeding And Genetics DNA STRUCTURE AND CHEMICAL COMPOSITION
  2. INTRODUCTION: • DNA called as the genetic blueprint as it carries the information from one generation to another. • It is the main constituent of chromosome. • It is the genetic material of all organism. • In bacterial cells, in mitochondria and chloroplast single circular double stranded DNA is found. • In Eukaryotic cell linear helically coiled double stranded DNA present inside the nucleus & its number equivalent to number of chromosome per cell.
  3. CHEMICAL COMPOSITION OF DNA • DAN is called as poly deoxy ribonucleotide molecule due to repeating of deoxy ribonucleotides. • These nucleotides are formed by nucleosides and phosphate and nucleosides are formed by nitrogenous bases and deoxyribose sugar. DNA = Nitrogenous base + Deoxyribose Sugar + Phosphate Nitrogenous base + Deoxyribose Sugar= nucleosides Nucleosides + Phosphate = Nucleotides
  4. NITROGENOUS BASES : PURINE: PYRIMIDINE: • Double ring structure having a pyrimidine ring and an imidazole ring. • It consists of 9 members • Nitrogen present at 1,3,7 and 9 position. • N-9 always binds to sugar. • Single ring structure. • It consists of 6 members. • Nitrogen present at 1 and 3 position. • N-1 always binds to sugar.
  5. DEOXY RIBOSE SUGAR (C₅H₁₀O₄): • It is a pentose sugar. • 5 membered ring with one Oxygen and 4 carbon. C-2 has H instead of –OH so it is called as deoxyribose. • It binds to base by β-N glycosidic linkage. • Derivative of phosphoric acid and gives acidity to DNA molecule. • It binds to sugar by phosphodiester bond. PHOSPHATE:
  6. NUCLEOSIDES: • Bases binds to sugar to form Nucleosides. • N-9 of Purine and N-3 of Pyrimidine binds to C-1 of sugar. • it is of 4 types- dA(Deoxyadenosine) dG(Deoxy guanosine) dC(Deoxy cytidine) dT(Deoxy thymidine) NUCLEOTIDE: • Nucleoside binds with phosphate to form nucleotide. • It is of 4 types – dAMP , dTMP, dGMP, dCMP
  7. BONDS IN DNA : • A pairs with T by 2 hydrogen bond and C with G by 3 hydrogen bond . T A • Sugar links to phosphate by phosphoester bond and to bases by glycosidic bond. G C Phosphoester bond Glycosidic bond Hydrogen bond
  8. DISCOVERY OF DNA DOUBLE HELIX : Double helical structure of DNA was proposed by J D Watson and F S C Crick(1953). This structure of DNA is based on X ray crystallographic studies on DNA done by Wilkins and Rosalind Franklin .
  9. Watson & Crick proposed… • A DNA molecule consist of 2 polynucleotide chains called as strands , coiled around a common axis to form right handed helix . • This coiling forms interchain spacing called major and minor grooves to which histone and non-histone protein interact . • ANTI-PARALLEL STRAND : One strand runs from 3′5′ and other from 5′3′ . • Sugar and phosphate form the periphery and the core is formed by nitrogenous bases. • BASE COMPLIMENTARITY : 6 aminopurine always link to 6 kitopyrimidine and 6 kitopurine link to 6 aminopyrimidin. It follows Chargaff's Rule i.e A+T=C+G • Adenine must pair with Thymine & Guanine must pair with Cytosine. Their amounts in a given DNA molecule will be about the same.
  10. MEASUREMENTS OF DNA : • A DNA completes one turn at every 34 Aᵒ (3.4nm) which is called Helix. • One helix contains 10 basepairs called as steps. • Space between each step 3.4 Aᵒ . • Diameter of B-DNA is 20 Aᵒ . • A major groove is about 22 Aᵒ • A minor groove is about 12Aᵒ
  11. Function of DNA : • It is the genetic material of all organism except some viruses . • It can form the exact copy of its own kind . This is called as replication. • It helps in synthesis of mRNA . This process is called as transcription. Conclusion: The structure of DNA given by Watson and Crick resembles with winding staircase where sugar and phosphate form the railings and linked bases formed the steps . This model have similarities with X-ray crystallography study of DAN . Therefore this structure is universally accepted.