process of transcription ( Fig. . ). In bacteria, since the mRNA does not require any processing to become active and also since transcription and translation take place simultaneously in the same compartment (since there is no separation of cytosol and nucleus in bacteria), many times the translation can begin much before the mRNA is fully transcribed.
This is because the genetic material is not separated from other cell organelles by a nuclear membrane consequently; transcription and translation can be coupled in bacteria. Promoter RNA polymerase Initiation Sigma factor DNA helix Elongation Terminator Termination RNA RNA RNA Polymerase Rho factor ' ' ' ' ' ' ' ' ' ' ' ' σ σ ρ Fig. . Process of transcription in prokaryotes XII Std Zoology Chapter XII Std Zoology Chapter Molecular Genetics DNA molecule?
Are they written in coded language on a DNA molecule? If they occur in the language of codes what is the nature of genetic code? The translation of proteins follows the triplet rule; a sequence of three mRNA base (a codon) designates one of the different kinds of amino acids used in protein synthesis. Genetic code is the sequence relationship between nucleotide in genes (or mRNA) and the amino acids in the proteins they encode.
There are possible triplets, and of them are used to represent amino acids. The remaining three triplet codons are termination signals for polypeptide chains. Since there are only amino acids involved in protein synthesis, most of them are encoded by more than one triplet. Two things make this multiple (degenerate) coding possible.
First, there is more than one tRNA for most amino acids. Each tRNA has a different anticodon. Second, this pairing is highly specific for the first two portions on the codon, permitting Watson and Crick base pairs (A – U and G - C) to be formed. But at the third position there is a great deal of flexibility as to which base pairs are acceptable.
Most part of the genetic code is