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.
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.
(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′ → 3′ direction. 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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