Brief Notes on Translation in Central Dogma

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Translation is the second step in the Central Dogma where the genetic information contained in mRNA transcript is transferred to proteins or polypeptides. Precisely speaking the genetic information as the nucleotide sequence of mRNA is translated into amino acid sequence of protein or polypeptide.

Translation takes place in complex cytoplasmic machinery made up of tRNAS, ribosomes and enzymes. It is important to note that all the three types of RNAs are involved in translation. The mRNA and tRNA participate directly in the process whereas rRNA participates as a component of ribosome, the site of translation.

Translation starts when an rRNA molecule in ribosome recognizes and binds specifically to a “start” site on mRNA. The ribosome then moves along mRNA three nucleotides at a time. Each group of three nucleotides is thus a code defining the next amino acid in the polypeptide chain. The Genetic Code Francis Crick and his colleagues in 1961 through an experiment in viral

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DNA concluded that the genetic code is triplet (read in increments consisting of three nucleotides) and that reading occurs continuously without punctuation between the three-nucleotide units. A triplet of nucleotides specifying a particular amino acid is known as a codon and thus, there should be 64 possible codons made out of four nucleotides taking three at a time (4 [1] )

Once the triplet nature of the codon was established different scientists then tried to establish the codons for twenty different amino acids found in proteins. Marshall Nircnberg in 1961 used a synthetic mRNA of Uracil only and found that the translated polypeptide was composed of Phcnylalanin amino acids only. Thus it was established that UUU is the codon of phenylalanine.

Then in 1964 Nircnbcrg and Philip Ledcr by employing the technique of triplet binding assay found out some 47 of the 64 possible codons. Har gobind Khorana worked out the remaining 17 codons by employing artificial mRNA. For this work Nircnbcrg and Khorana shared the Nobel prize in 1968 with R.W.Holley who gave details of tRNA structure.

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