Genetic code, an introduction

GENITIC CODE

How do nucleotides in mRNA  molecules specify the AA the segment in proteins ?

With 4 different nucleoids ( A , C G , U ) a three letter code generate 64 possible codes.

Genetic code : collections of basic sequences that respond to each  amino acid and stop signals  for translate .

1960- Francis Crick , Leslie Barnett , Sidney Berner , Watts Tobin

There are several ways in which a codes could be read from a mRNA  molecule .

Two most important ways are :

Ø  Overlapping codes

Ø  Non overlapping codes

 

In overlapping model

Each base serves as  first base of some codon . After the first amino acid  in a protein is coded the next two and for that matters the remaining amino acids in the protein are particularly pre determined .

Non overlapping model

Mutation allow change in one base single mutagenic base change could after as many as 3 amino acids .

 If mRNA  strand      :  ABC  DAB CDA

In Overlapping model

ABC       BCD     CDA   

 In Non overlapping

ABC   DAB   CDA

Commonly used in start codes --  AUG

 In few instances --  GUG

 Stop codes –UAG(amber), UAA(Ochre) , UGA(Opal)

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