Nucleic acids


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Nucleic acids

  1. 1. Nucleic Acids
  2. 2. Nucleic Acids Are Essential For Information Transfer in Cells • Information encoded in a DNA molecule is transcribed via synthesis of an RNA molecule • The sequence of the RNA molecule is "read" and is translated into the sequence of amino acids in a protein.
  3. 3. Replication DNA replication yields two DNA molecules identical to the original one, ensuring transmission of genetic information to daughter cells with exceptional fidelity. Transcription The sequence of bases in DNA is recorded as a sequence of complementary bases in a singlestranded mRNA molecule.
  4. 4. Translation Three-base codons on the mRNA corresponding to specific amino acids direct the sequence of building a protein. These codons are recognized by tRNAs (transfer RNAs) carrying the appropriate amino acids. Ribosomes are the “machinery” for protein synthesis.
  5. 5.  First discovered in 1869 by Miescher.  Found as a precipitate that formed when extracts from nuclei were treated with acid.  Compound contained C, N, O, and high amount of P.  Was an acid compound found in nuclei therefore named nucleic acid
  6. 6.  1944 Oswald, Avery, MacLeod and McCarty demonstrated that DNA is the molecule that carrier genetic information.  1953 Watson and Crick proposed the double helix model for the structure of DNA
  7. 7.  Nucleic acids are long polymers of nucleotides.  Nucleotides contain a 5 carbon sugar, a weakly basic nitrogenous compound (base), one or more phosphate groups.  Nucleosides are similar to nucleotides but have no phosphate groups.
  8. 8. Pentoses of Nucleotides • D-ribose (in RNA) • 2-deoxy-D-ribose (in DNA) • The difference - 2'-OH vs 2'-H • This difference affects secondary structure and stability
  9. 9. • Base is linked via a b-N-glycosidic bond • The carbon of the glycosidic bond is anomeric • Named by adding -idine to the root name of a pyrimidine or -osine to the root name of a purine • Conformation can be syn or anti • Sugars make nucleosides more water-soluble than free bases
  10. 10. Anti- conformation predominates in nucleic acid polymers
  11. 11. Phosphate ester of nucleosides
  12. 12. Other Functions of Nucleotides • Nucleoside 5'-triphosphates are carriers of energy • Bases serve as recognition units • Cyclic nucleotides are signal molecules and regulators of cellular metabolism and reproduction
  13. 13.  ATP is central to energy metabolism  GTP drives protein synthesis  CTP drives lipid synthesis  UTP drives carbohydrate metabolism
  14. 14.  Nucleotide monomers are joined by 3’-5’ phosphodiester linkages to form nucleic acid (polynucleotide) polymers
  15. 15.  Nucleic acid backbone takes on extended conformation.  Nucleotide residues are all oriented in the same direction (5’ to 3’) giving the polymer directionality.  The sequence of DNA molecules is always read in the 5’ to 3’ direction
  16. 16. •Guanine pairs with cytosine •Adenine pairs with thymine
  17. 17. Base compositions experimentally determined for a variety of organisms
  18. 18. H-bonding of adjacent antiparallel DNA strands form double helix structure
  19. 19.  Distance between the 2 sugar-phosphate backbones is always the same, give DNA molecule a regular shape.  Plane of bases are oriented perpendicular to backbone  Hydrophillic sugar phosphate backbone winds around outside of helix
  20. 20.  Noncovalent interactions between upper and lower surfaces of base-pairs (stacking) forms a closely packed hydrophobic interior.  Hydrophobic environment makes H-bonding between bases stronger (no competition with water)  Cause the sugar-phosphate backbone to twist.
  21. 21. Hydrophobic Interior with base pair stacking Sugar-phosphate backbone
  22. 22.  Right handed helix  Rise = 0.33 nm/nucleotide  Pitch = 3.4 nm / turn  10.4 nucleotides per turn  Two groves – major and minor
  23. 23.  Within groves, functional groups on the edge of base pairs exposed to exterior  involved in interaction with proteins.
  24. 24.  Hydrophobic interactions – burying hydrophobic purine and pyrimidine rings in interior  Stacking interactions – van der Waals interactions between stacked bases.  Hydrogen Bonding – H-bonding between bases
  25. 25.  Charge-Charge Interactions – Electrostatic repulsions of negatively charged phosphate groups are minimized by interaction with cations (e.g. Mg2+)