When the RNA polymerase arrives at the terminator codon (stop signal) disengages from the DNA and releases the newly assembled RNA chain called Pre-mRNA . The chain is a complimentary transcript of the genetic code from which it was copied. The processed pre-mRNA strand leaves the nucleus and travels to the ribosomes .
b) Translation
Translation is the second step in Protein synthesis. Translation is the transfer of information from mRNA to protein, which occurs when the information contained in the mRNA transcript is used to direct the sequence of amino acids during synthesis of polypeptides by the ribosomes.
Translation Process:
The rRNA molecule within the ribosome binds to the (start) codon on the mRNA. The mRNA lies on the ribosome in such a way that only one of its codons is exposed at the polypeptide making site at any time. A tRNAmolecule possessing the “complimentary” triplet sequence ( anticodon ) binds to the exposed codon on the mRNA. Because this tRNA molecule carries a particular amino acid, that amino acid and no other is added to the polypeptide in that position. The ribosome moves along the mRNA molecule three nucleotides at a time or one triplet at a time. Successive codons on the mRNA are exposed and a series of tRNA molecules bind one after another to the exposed codons. The ribosome continues until it encounters the “stop” codon and then disengages from the mRNA and releases the completed polypeptide.
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