SU 2

• Gregor Mendel discovers the laws of inheritance


  1865
• Friedrich Miescher discovers nucleic acids


  1869
• Carl Correns, Erich von Tschermak-Seysenegg and Hugo de Vries rediscovers Mendel's work


  1900
• Walter Stanbrough Sutton proposes that chromosomes are found in pairs and that they are the elements of inheritance

  1902
• Oswald Avery, Collin MacLeod and Maclyn McCarthy demonstrate DNA is the genetic material


  1944
• Chargraff's rules


  1950
• Rosalind Franklin develops X-ray picture of DNA


  1952
• James Watson and Francis Crick use Franklin's picture to describe the structure of DNA molecule


  1953

  
• Marshall Nirenberg, Heinrich Mathaei and Severo Ochoa explain genetic code of DNA


  1966
• Herbert Boyer and Stanley Cohen develop basic techniques for cloning and with that, recombinant DNA technology – introduce the new area of biology


  1973
• Production of the first commercial recombinant protein, insulin, by Genentech inc


  1978
• Kary Mullins develops PCR technique


  1987
• Cloning of the sheep "Dolly"


  1997
• Human genome project


  1990 – 2003
• Nucleotides


  Biological molecules
• Components of nucleotides


  • Heterocyclic nitrogenous base
  • 5-carbon sugar (pentose)
  • Phosphate group

  
• Several nucleotides combine to form nucleic acids
• The order or sequence of the nucleotides encode information
• Nucleic acids are the agents which house and transfer genetic information
• DNA


  Sugar is deoxyribose
• RNA


  Sugar is ribose
• DNA is the repository of genetic information in cells
• RNA leads to the expression of this information
• Viruses store their genetic information as RNA
• Pyrimidines and purines


  • They undergo tautomerization due to aromatic nature and carbonyl ring N2 substituents which are electron rich
  • At physiological conditions, keto forms dominate

  
• pKa values for ring nitrogen atoms


  • They specify whether protons associate with ring N2 at neutral pH
  • Determines whether N2 will serve as H acceptors or donors

  
• H2 bonding between pyrimidines and purines is important to the biological function of nucleic acids

  
• Main functional groups involved in H bonding

  • Amino groups of C, A and G
  • Ring N2 at position 3 of pyrimidines
  • Ring N2 at position 1 of purines
  • Strong electronegative oxygens atoms of U, T, C and G

  
• Nitrogenous bases absorb UV light due to aromatic heterocyclic ring structures
• This is important for qualitative and quantitative and assessment of nucleotides and nucleic acids
• The properties of pyrimidines and purines can be traced to their electron-rich nature

  
• Nucleosides


  Composed of sugar (ribose and deoxyribose) and heterocyclic base (purine or pyrimidine)

  
• Structure of nucleoside (of ribonucleoside)

  The base is linked to the sugar via a glycosidic bond

  
• Nucleotides


  Composed of ribose/deoxyribose, heterocyclic base (=nucleoside), and phosphate linked to nucleoside via phosphoester bond

  
• AMP → ADP → ATP


  Additional phosphate groups can be added to the phosphoryl group of nucleotide via phosphoric anhydride linkages
• Nucleotide 5' – triphosphates are indispensable in metabolism</b>

  
• Phosphoric anhydride linkages are a rich source of chemical energy
• Biochemical reactions of nucleotides involve group transfers, not the base and sugar
• Nucleotides


  Polyprotic acids that supply chemical energy
• Nucleoside di and triphosphate molecules

  • They are polyprotic, i.e. can dissociate 3 and 4 protons from their phosphoric acid groups