Bacterial Transcription

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Chapter: Pharmaceutical Microbiology : Microbial Genetics and Variations

Bacterial transcription refers to the – ‘synthesis of a complementary strand of RNA particularly from a DNA template’.

Bacterial Transcription


Bacterial transcription refers to the – ‘synthesis of a complementary strand of RNA particularly from a DNA template’.


In fact, there exists three different types of RNA in the bacterial cells, namely : (a) messenger RNA ; (b) ribosomal RNA, and (c) transfer RNA.


Messenger RNA (mRNA) : It predominantly carries the ‘coded information’ for the produc-tion of particular proteins from DNA to ribosomes, where usually proteins get synthesized.


Ribosomal RNA : It invariably forms an ‘integral segment’ of the ribosomes, that strategically expatiates the cellular mechanism with regard to protein synthesis.


Transfer RNA : It is also intimately and specifically involved in the protein synthesis.


Process of Bacterial Transcription :


Importantly, during the process of bacterial transcription, a strand of messenger RNA (mRNA) gets duly synthesized by the critical usage of a ‘specific gene’ i.e., a vital segment of the cell’s DNA–as a template, as illustrated beautifully in Figure : 6.6. Thus, one may visualize the vital and important ‘genetic information’ adequately stored in the sequence of nitrogenous bases (viz., A, T, C and G) of DNA, that may be rewritten so that the same valuable ‘genetic information’ appears predominantly in the base sequence of mRNA.


Examples :


(1) In the DNA replication phenomenon, it has been duly observed that a G in DNA template usually dictates a C in the mRNA ; and a T in DNA template invariably dictates an A in the mRNA.


(2) An A in DNA template normally dictates a uracil (U) in the mRNA by virtue of the fact that RNA strategically contains U instead of T*.


(3) In an event when the template segment of DNA essentially possess the base sequence ATG-CAT, consequently the strategic newly synthesized mRNA strand shall predominantly would bear the complementary base sequence UAC GUA.


Salient Requirements : The salient requirements for the process of bacterial transcription are as enumerated under :


(1) It essentially needs two cardinal components, namely :

(a) RNA– polymerase — an ‘enzyme’, and

(b) RNA–nucleotides — a regular and constant supply.


(2) Promoter — Usually transcription commences once the RNA polymerase gets strategi-cally bound to the DNA at a specific site termed as ‘promoter’.


(3) Precisely, only one of the two DNA strands invariably caters as the particularly required ‘template for the synthesis for a given ‘gene’.


Examples : There are several typical examples that explains the above intricate phenomenon vividly :


(a) Just as DNA, the RNA gets synthesized duly and specifically in the 5 3direction. Nevertheless, the ‘equivalence point’ (i.e., endpoint) for transcription of the gene is signaled suitably by a terminator segment present strategically in the DNA. Interestingly, at this particular zone, one may observe the release from the DNA of these two entities prominently : (i) RNA polymerase ; and (ii) newly generated single-stranded mRNA.


(b) ‘Regions of genes’ present critically in ‘eukaryotic cells’ which essentially afford ‘coding’ for the respective proteins are usually interrupted by the so-called ‘noncoding DNA’. There-fore, the ‘eukaryotic genes’ are made up of ‘exons’ i.e., the specific segments of DNA expressed appropriately ; besides, ‘introns’ i.e., the designated intervening segments of DNA which fail to code for the corresponding protein. Besides, in the eukaryotic cell the nucleus predominantly synthesizes RNA polymerase from the entire gene–a fairly long and continuous RNA product* usually termed as the RNA transcript.


Mechanism : The ‘elongated RNA’ is subsequently processed by a host of other enzymes that particularly help in the removal of the intron-derived RNA and also splice together the exon derived RNA thereby producing an mRNA which is exclusively capable of ‘directly the on-going protein synthesis’. Consequently, the RNA gracefully walks out of the nu-cleus, and ultimately turns into a mRNA of the ensuing cytoplasm.


Ribozymes — are non protein enzymes (i.e., a RNA enzyme) duly obtained as a result of certain enzymes which are actually cut by the RNA itself.


(c) Importantly, in eukaryotic organisms, the ensuing transcription usually occurs in the nucleus. It has been observed that mRNA should be completely synthesized and duly moved across the nuclear membrane right into the cytoplasm before the actual commencement of the phenomenon of translation. Besides, mRNA is duly subjected to further processing mode before it virtually gets out of the nucleus.


Summararily, the valuable genetic information, derived from prokaryotes and eukaryotes, pertaining to protein synthesis is stored meticulously in DNA, and subsequently passed on to mRNA during the phenomenon of ‘transcription’. Ultimately, mRNA prominently serves as the source of information for the required protein synthesis.


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