CONCLUSIONS
(Khorana's paper on " Polynucleotide synthesis and the genetic code", 1965)

The following conclusions were reached in the experiments to unravel the genetic code by H.G. Khorana:

      DNA specifies the sequence of amino acids in proteins and the information is realyed through a RNA molecule.  This enabled direct correlation between DNA and a protein to be accomplished.

  An amino acid is translated from a 3-letter, non-overlapping nucleotide sequence as opposed to a 2- or 1-
     letter code from messenger RNA.
        - the proof of this is present in the nature of the genetic code
        - the above statement is valid, however, it does not rule out the fact that a single mRNA (messenger RNA)
          may have multiple initiation points for translation. Therefore there will be different reading frames within
          the same mRNA, and hence specification for more than one polypeptide chain (overlapping genes).
          Four cases of overlapping genes discovered, for example in viruses. (Fig 1).
 

  The genetic code table proposed by Khorana differs in some aspects to the table which is present today
      (Fig 2).

  Codon assignments(which code stands for which amino acid) for Escherichia coli:
          a) "the code as shown for E.coli, will probably hold essential for other organisms as well" (Khorana, 1965)
                - we know today that the genetic code is nearly universal
                - in other words the genetic code varies in certain aspects for mitochondrial DNA (mtDNA), for
                  example UGA in  the normal code is a stop codon and in mtDNA in humans and yeast it codes for
                  trptophan.
          b) "two meanings for a few of the codons, for example AUG and GUC stand for insertion of amino acids
                and for chain initiation signals" (Khorana, 1965)
                - valid statement to present knowledge, but only AUG is initiator code.
          c) the code is highly degenerate, and there are enteries for all of the 64 trinucleotides
              - today we know through Crick's work in 1966 that degeneracy is due to the wobble position
          d) there are two chain termination codons, UAA and UAG but not known whether UGA is termination
               code or nonsense
              -today it is established that there aree three stop codes UAA,UGA and UAG.

  Two binding sites on a 70s ribosmal particle
           - 30s and 50s ribosmal involved in protein synthesis
           - 30s particles bind fmet-tRNA in presence of poly-AUG
           - noninitiator tRNA's are bound only after the addition of 50s particle to 30s particle
           - possible to carry out the dipeptide, formylmethionylmethionine, synthesis by stepwise formation of
                  appropriate complex containing all necessary components