presentation explain the general Characteristic of genetic code as well as biological significance of the degeneracy.

2.  The relationship between the
sequence of bases in DNA /RNA and
the sequence of amino acids in a
polypeptide chain of protein / enzyme
is called as GENETIC CODE.
 It contain base sequence of DNA.
 The term was coined by “Goerge
Gamow”
 Examples : AUG, UUU, ACC, UAG, etc.
The characteristics of genetic code
are explain as follows,

5.  In non-overlapping code, each nitrogen base
is read only once and six nucleotides would
code for two amino acids
 But in overlapping code , one nitrogen base
would be read three times, each time as a
part of different code and six nucleotides
would code for 4 AA.
C A T G A T (Non–Overlapping code)
aa1 aa2

6.  The genetic code must be read in fixed
direction i.e. the code has polarity.
 Always read from left to right (5’ 3’)
direction rise to correct protein /enzyme.
 If the code is read from opposite direction
then protein will change and undergo drastic
change.
UUG AUC GUC
5’ 3’ Leu Ileu Val
Val Leu Leu 3’ 5’

7.  AUG is starting or initiation codon and
initiates the protein synthesis of polypeptide
chain. AUG codes for aa Methionine in
eukaryotes and N-formyl methionine in
prokaryotes. Less often, GUG also serve as
intiation codon which codes for Valine…
 UAG, UAA and UGA are the termination
codon. This codons do not specify any amino
acid so, is called as Nonsense codon. They
terminates the protein synthesis…

8.  Nirenberg demonstrated the universality of the
code. A codon specifies the same amino acid
from bacteria to tree and human being, etc.
and hence it is biologically universal.
 Non-ambiguous means that a particular codon
will always code for the same amino acid. If
codon code for another amino acid in presence
of external factor, then it said to ambiguous.
 The sequence of codon in DNA or mRNA
corresponds to the sequence of amino acid in
the polypepetide manufactured under the
guidance of mRNA so, it has colinearity.

9.  There are 61 codons which codes for 20
different amino acids, it is obvious that,
there are many more codons than amino
acids.
 Except for tryptophan and methionine, which
have a single codon each, all other amino
acids have more than one codon (2 to 6
codon) and they are called as degenerate
codons.
 In this codon, the first two nitrogen bases
are similar while the third one is different.
As the third nitrogen base has no effect on
coding, it called as wobble position.

10.  The effect of mutation is reduced.
 The number of tRNA required is reduced.
 Degeneracy is also help in evolution of
organisms.
 Degeneracy is help in repair mechanism of
various types of mutations.