Genetic codon

Brief description about genetic codon and its characteristics. Degeneracy of genetic code, Open reading frame, Reading Frame etc

1. Genetic Code By, Dr. Kayeen Vadakkan Assistant Professor, Department of Biotechnology St. Mary's College Thrissur, Kerala , India

2. Topics Covered Genetic Code Discovery of Genetic Code Characteristics of Genetic code Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur

3. Genetic Code Definition The genetic code is a triplet of nucleotides that codes for a specific amino acid. A U A C G A G U C Triplet Codon Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur

4. Discovery of genetic code The discovery of genetic code and translation was based on the experiments and observations made by three independent group of scientists. Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur

5. Discovery 1 In 1950, Paul Zamecnik and his team discovered that the site of protein synthesis is ribosomes Discovery 2 Mahlon Hoagland and Paul Zamecnik discovered that the amino acids are activated when incubated with ATPs Discovery 3 Francis Crik discovered that how genetic informations are coded in 4 letter language (ATGC) A nucleic acid can function as adaptor where in one part bind with amino acid and one with mRNA. Genetic Code Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur

6. Characteristics of genetic code Translation occurs when genetic code is read in successive , non overlapping way There is a possibility that the genetic code may be read in either over lapping manner or non over lapping manner A U A C G A 1 2 3 Overlapping Code A U A C G A 1 2 Non- Overlapping Code In overlapping code same nucleotide in mRNA will be shared by different codon, however in non-overlapping codon nucleotides are not shared by codon. In all living organisms the genetic code is non-overlapping Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur

7. Characteristics of genetic code (Continues) 2. Reading frame of Genetic Code It is the specific first codon in a mRNA sequence. A new codon begins at each three nucleotide residue T here is no punctuation between these triplet codons The amino acid sequence is determined by the linear sequence of continuous triplets. There is a possibility that in a single mRNA shall have various reading frame U U C U C G G A C U U C U C G G A C U U C U C G G A C Reading Frame I Reading Frame II Reading Frame III Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur

8. Characteristics of genetic code (Continues) 3 . 64 Triplet Codons There are total 64 triplet codons present in mRNA Termination Codon : The termination codon UAA, UAG, UGA are also called as the stop codons/Non-sense codon. They stop the synthesis of amino acids and does not code for any known amino acids. In general in a reading frame one in every 20 codons will be a termination codon Initiation Codon : The initiation codon (AUG) are the common signal for the beginning of protein synthesis. Open Reading Frame : A reading frame without a termination codon for fifty or more codons are referred as open reading frame Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur

9. Characteristics of genetic code (Continues) 4 . Degeneracy of Genetic Code Definition The phenomenon through which a single amino acid may be specified by more than one codon is called the degeneracy of genetic code. The degeneracy of genetic code is not uniform Example : there are 6 different codons present in mRNA that codes for Arginine, three codons for Isoleucine and only one codon for Methionine U C G C C G A C G G C G G A A G G A Arginine Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur

10. Further reading Lehninger Principles of Biochemistry by Michael M Cox and David L Nelson Molecular Biology of the Genes – J.D.Watson , N.H.Hopkins Moleculary Cell Biology, J.Darnell , H.Lodish Gene VIII, Benjamin Lewin Genomes , T.S.Brown Molecular Cloning: a Laboratory Manual, J.Sambrook . Molecular Biology, Kayeen Vadakkan, Department of Biotechnology, St. Mary's College, Thrissur