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Transcription
The “central dogma” of molecular biology: DNA makes messenger RNA
makes protein
...
Transcription is the production of RNA
from this DNA
...
Such mRNA
sequences are also referred to as “transcripts”
...
Thus, many or even most
of the genes may not be required to be expressed at a given time in a given cell
...
How then should the genome be regulated? Should all the genes be constitutively
expressed, with expression of many genes being inhibited by some process or
mechanism? Alternatively, should expression of all the genes be constitutively
prevented, with those that are necessary being specifically activated? What are
the implications of these two proposed mechanisms?
In the eukaryotic genome, most genes are “off” and are switched “on” when
needed
...
Furthermore, in a single
cell organism, with no tissue specialisation, more of the genes of the genome
will be required to be expressed
...
NOMENCLATURE
Sites on DNA are classified by their position in relation to genes and
transcription start sites
...
This is, therefore, said to be “upstream of” or “5’
to” the start site
...
In transcription nomenclature there is no base zero; the last base of the
promoter is termed base −1, and the bases “upstream” of the transcriptional start site
(sometimes referred to as the “tsp”) are numbered negatively
...
DNA binding is mediated by distinct domains in transcription factors, some
of which can confer DNA-binding activity on proteins that ordinarily do not
bind DNA, when joined artificially to them in chimeric proteins
...
This—in turn—is controlled largely at the level of the initiation of
transcription by RNA polymerase and to a lesser extent via alternative splicing
events during mRNA processing and other mechanisms
...
How does a transcription factor identify its target gene(s)?
the genes to be activated by a given transcription factor are those
containing the recognition sequence of the transcription factor in their promoters
...
Transthyretin is synthesised primarily by hepatocytes
...
Transcription factors binding to
these sites include C/EBP, HNF1 (hepatocyte nuclear factor 1), HNF3, HNF4 (a
C2H2 zinc finger protein), and API
...
Many hormones act via cell-surface receptors, which transduce an
extracellular message across the membrane to produce an intracellular
effect
...
a) transcription produces heterogeneous nuclear RNA (hnRNA)
...
c) The mRNA precursor is cleaved towards the 3’-end
...
e) The introns present are removed by splicing, leading to mature
mRNA
...
Several
proteins are involved in this process
...
The enzyme poly(A) polymerase
then tails the transcript, by adding approximately 200 A residues
...
PAGE
3
Splicing of eukaryotic mRNA
...
c) The mature mRNA is then ready for translation