Transcription transfers the genetic instructions from the DNA template to RNA and is the first step in expression of the genome . This highly regulated process consists of the synthesis of an RNA molecule by an RNA polymerase (RNA pol) that reads the template (or noncoding) strand of the DNA; the primary transcript will therefore carry the same genetic message as the other DNA strand, namely the coding strand.
Translation is the synthesis of a protein according to the genetic information. It is the second step of gene expression, following transcription, and is a universal and essential step for life. The process is called translation because it converts the genetic information of nucleic acid sequences, composed of four distinct nucleotides, to the polypeptide sequence composed of 20 distinct amino acids. An enzyme called aminoacyl-tRNA synthetase adds the correct amino acid to its tRNA. Amino acids are joined together in proteins by peptide bonds. This is carried out by the enzyme peptidyl synthetase. An initiation complex for translation forms by the assembly of the ribosomal subunits and initiator tRNA (met-tRNA) at the start codon on the mRNA. Several ribosomes can translate an mRNA at the same time, forming what is called a POLYSOME.
In a prokaryotic cell, transcription and translation are coupled; that is, translation begins while the mRNA is still being synthesized. In a eukaryotic cell, transcription occurs in the nucleus, and translation occurs in the cytoplasm.
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Why is transcription coupled to translation in bacteria?
