The Genetic Code of mRNA

The Genetic Code of mRNA - Fig 4 Because there are 4...

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The Genetic Code of mRNA The universal Genetic Code was deciphered in the early 1960s. It is a triplet code. In other words, each sequence of 3 mRNA nucleotides is a codon which corresponds to one amino acid. Example: 5'- A U G U U U C G U A C G U A A - 3' N- Met - Phe - Arg - Thr -C Each codon - codes for a specific amino acid or serves as a stop codon . (Stop codons are: UAA, UAG, UGA These three codons do not code for an amino acid. They signal as a stop signal for translation. ) The Start codon is AUG. AUG codes for the amino acid, methionine , so every protein initially begins its sequence with methionine regardless of whether it is a prokaryotic or eukaryotic protein. There are 3 possible reading frames on a message depending upon where you start. So punctuation is very important (AUG) codon critical (
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Unformatted text preview: Fig. 4 ). Because there are 4 different nucleotides, and it is a triplet code-- there are -- 4 3 =64 possible codon triplets for only 20 different amino acids. Therefore, most amino acids are specified by more than 1 codon-- in other words the genetic code is a degenerate code . An example, all of the following codons code for the amino acid arginine: CGU CGC CGA CGG The Genetic code also is highly conserved, the same in organisms as diverse as bacteria, plants, and man. There are as many different mRNAs as there are genes. Most proteins have between 100 and 1,000 amino acids so an mRNA must be at least between 300 and 3,000 nucleotide bases long. Each mRNA possesses codons that are read by tRNAs ....
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