Genetic code

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Genetic code

  1. 1. Genetic Code and its Co-relation with Wobble - Hypothesis
  2. 2. Genetic Code ● Consists of a “TRIPLET “, i.e. A sequence of 3 bases codes for a particular amino acid . ● There are 4³ or 64 possible combinations . ● Group of 3 bases coding for an amino acid in mRNA is called a codon PROPERTIES : ● Degenerate : An amino acid can be coded for by more than one codon. Anti codon shows Wobble . ● Unambiguous : Each codon indicates a single , specific amino acid . ● Non-overlapping : When translated , the reading frame is advanced 3 bases at a time .
  3. 3. Genetic Code
  4. 4. Contd. . ● The base sequence is read from a fixed point , without any punctuations. ● Out of 64 codons , 61 codons specify amino acid , while remaining 3 are nonsense or stop codons. ● The code is degenerate - except for Trp and Met,each amino acid is coded by two or more codons . ● Codons are recognized by aminoacyl-tRNAs. ● Aminoacyl-tRNAs activate the amino acid for transfer to peptide ● Aminoacyl-tRNA synthetases does the critical job : linking the right amino acid with "cognate" tRNA ● Reaction: amino acid + ATP → aminoacyl-AMP + Ppi aminoacyl-AMP + tRNA → aminoacyl-tRNA + AMP Sum of 1 and 2: amino acid + tRNA + ATP → aminoacyl-tRNA + AMP + PPi
  5. 5. Wobble in the anti codon : ● In 1966, Francis Crick ,proposed “the Wobble hypothesis”.According to this hypothesis, only the first two bases of the codon have a precise pairing with the bases of the anticodon of mRNA, while the pairing between the third bases of codon and anticodon may Wobble (non specific). ● The pairing between the first two bases is normal, while between G and U is against the normal pairing pattern. This unusual bonding between G and U is called Wobble pairing. ● Inosine is the fifth base in the anti codon. ● Inosine arises through enzymatic modification of adenine by ADAR-Adenosine Deanimase RNA specific . ● Inosine is commonly found in tRNAs and is essential for proper translation of the genetic code in wobble base pairs. ● Advantage of wobble: dissociation of tRNA from mRNA is faster

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