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Dna and rna


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Dna and rna

  1. 1. DNA and RNA The Blueprint of Life Dr. Gangadhar Chatterjee
  2. 2. Nucleotides, Building Blocks of Nucleic Acids (1) a nitrogenous (nitrogen-containing) base (2) a pentose (3) a phosphate
  3. 3. Nucleotide and Nucleic Acid Nomenclature
  4. 4. Nucleic acids have two kinds of pentoses Recurring deoxyribonucleotide units of DNA contain 2’deoxy-D-ribose the ribonucleotide units of RNA contain D-ribose both types of pentoses are in their β-furanose (closed five-membered ring) form. pentose ring is not planar
  5. 5. Phosphodiester Bonds Link Successive Nucleotides in Nucleic Acids
  6. 6. RNA is hydrolyzed rapidly under alkaline conditions, but DNA is not; covalent backbone of DNA and RNA is subject to slow, nonenzymatic hydrolysis of the phosphodiester bonds.
  7. 7. Nucleic Acid Structure first isolated and characterized by Friedrich Miescher in 1868 • Oswald T. Avery, Colin MacLeod, and Maclyn McCartyStreptococcus pneumoniae • Alfred D. Hershey and Martha Chase -bacteriophage with radioactively labeled DNA • Erwin Chargaff – his conclusions
  8. 8. 1. The base composition of DNA generally varies from one species to another. 2. DNA specimens isolated from different tissues of the same species have the same base composition. 3. The base composition of DNA in a given species does not change with an organism’s age, nutritional state, or changing environment
  9. 9. A structure this pretty just had to exist. —James Watson, The Double Helix, 1968 James Watson and Francis Crickpostulated a threedimensional model of DNA structure
  10. 10. Watson-Crick model for the structure of DNA
  11. 11. DNA Can Occur in Different Three-Dimensional Forms steric constraint-purines in purine nucleotides restricted to two stable conformations with respect to deoxyribose- SYN & ANTI Pyrimidines are generally restricted to the anti conformation
  12. 12. Structural variation in DNA. B-DNA : most commonly occurring A-DNA -favored in many solutions that are relatively devoid of water Z-DNA: Left handed helix
  13. 13. Certain DNA Sequences Adopt Unusual Structures bends occur in the DNA helix wherever four or more adenosine residues appear sequentially in one strand DNA Palindrome: regions of DNA with inverted repeats of base sequence having twofold symmetry over two strands of DNA
  14. 14. Hairpins and cruciforms
  15. 15. mirror repeat When the inverted repeat occurs within each individual strand of the DNA cannot form hairpin or cruciform structures
  16. 16. unusual DNA structures- DNA Triplex & G tetraplex The N-7, O6, and N6 of purines, the atoms that participate in the hydrogen bonding of triplex DNA- referred as Hoogsteen positions non-Watson-Crick pairing called Hoogsteen pairing
  17. 17. RNA
  18. 18. Types of RNA 23
  19. 19. mRNA is like a waitress that takes your order or information so it can be made into your meal. The assistants to the chef is like the tRNA bringing the head chef the ingredients to make your meal The head chef is the rRNA, his job is to prepare the food
  20. 20. Messenger RNAs Code for Polypeptide Chains The process of forming mRNA on a DNA template is known as transcription Monocistronic- code for single polypeptide Polycistronic- code for two or more polypeptide
  21. 21. Many RNAs Have More Complex Three-Dimensional Structures product of transcription of DNA is always single-stranded RNA single strand tends to assume a right-handed helical conformation dominated by basestacking interactions Typical right-handed stacking pattern of single-stranded RNA. Stronger between two purines than between a purine and pyrimidine or between two pyrimidines
  22. 22. Secondary structure of RNA paired regions generally have an A-form righthanded helix hairpins are the most common type of secondary structure in RNA
  23. 23. Transfer RNAs Have Characteristic Structural Features Three-dimensional structure of yeast tRNAPhe deduced from x-ray diffraction analysis.
  24. 24. Nucleic Acid Chemistry Double-Helical DNA and RNA Can Be Denatured
  25. 25. Denaturation temperature, or melting point (tm; formally, the temperature at which half the DNA is present as separated single strands)
  26. 26. Hypochromic and hyperchromic effect Transition from double-stranded DNA to the singlestranded, denatured form can be detected by monitoring UV absorption at 260 nm
  27. 27. Nucleic Acids from Different Species Can Form Hybrids hybrid duplexes: -reflects a common evolutionary heritage -A specific DNA sequence or gene can be detected in the presence of many other sequences if one already has an appropriate complementary DNA strand
  28. 28. Nucleotides and Nucleic Acids Undergo Nonenzymatic Transformations Purines and pyrimidines undergo spontaneous alterations in their covalent structure Though very slow cells have very low tolerance for alterations in its genetic information --- MUTATION under typical cellular conditions, deamination of cytosine (in DNA) to uracil occurs in about one of every 107 cytidine residues in 24 hours Product of cytosine deamination (uracil) is readily recognized as foreign in DNA and repaired.
  29. 29. Depurination Deamination hydrolysis of the N-β-glycosyl bond between the base and the pentose
  30. 30. Radiation reactions
  31. 31. DNA damage by reactive chemicals Nitrous acid precursors Alkylating agents
  32. 32. most important source of mutagenic alterationsOXIDATIVE DAMAGE highly reactive chemical dimethylsulfate can methylate a guanine to yield O6methylguanine, which cannot base-pair with cytosine the integrity of DNA as a polymer is better maintained than that of either RNA or protein, because DNA is the only macromolecule that has the benefit of biochemical repair systems
  33. 33. The Sequences of Long DNA Strands Can Be Determined Alan Maxam and Walter Gilbert Frederick Sanger
  34. 34. The Chemical Synthesis of DNA has been Automated Dr. Hargovind Khurana
  35. 35. THANK YOU