Basic Principles of Transcription and Translation - Computer ...
Basic Principles of Transcription and Translation - Computer ...
Basic Principles of Transcription and Translation - Computer ...
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(a)<br />
(b)<br />
5′<br />
3′<br />
Primary miRNA transcript.<br />
This RNA molecule is<br />
transcribed from a gene in a<br />
nematode worm. Each<br />
double str<strong>and</strong>ed region that<br />
ends in a loop is called a<br />
hairpin <strong>and</strong> generates one<br />
miRNA (shown in orange)<br />
Regulation <strong>of</strong> gene<br />
expression by miRNAs. RNA<br />
transcripts are processed<br />
into miRNAs which prevent<br />
expression <strong>of</strong> mRNAs<br />
containing complementary<br />
sequences.<br />
Hairpin<br />
miRNA<br />
miRNA<br />
Hydrogen<br />
bond<br />
Dicer<br />
1) An enzyme cuts<br />
each hairpin from<br />
the primary miRNA<br />
transcript<br />
2) A second enzyme<br />
called Dicer, trims<br />
the loop <strong>and</strong> the<br />
single str<strong>and</strong>ed<br />
ends from the<br />
hairpin, cutting at<br />
the arrows.<br />
3) One str<strong>and</strong> <strong>of</strong> the<br />
double str<strong>and</strong>ed<br />
RNA is degraded;<br />
the other str<strong>and</strong><br />
(miRNA) then forms<br />
miRNAprotein<br />
a complex with one<br />
complex<br />
or more proteins<br />
4) The miRNA in the<br />
complex can bind to<br />
any target mRNA<br />
that contains at<br />
least 6 bases <strong>of</strong><br />
complementary<br />
sequence.<br />
5) If miRNA <strong>and</strong><br />
mRNA are<br />
complementary all<br />
along their length,<br />
the mRNA is<br />
mRNA degraded<br />
<strong>Translation</strong> blocked degraded (left); if<br />
the match is less<br />
(b) Generation <strong>and</strong> function <strong>of</strong> miRNAs<br />
complete translation<br />
is blocked (right)<br />
The phenomenon <strong>of</strong> inhibition <strong>of</strong> gene expression by RNA<br />
molecules is called RNA interference (RNAi).<br />
This is caused by single-str<strong>and</strong>ed small interfering RNAs<br />
(siRNAs) <strong>and</strong> can lead to degradation <strong>of</strong> an mRNA or block<br />
its translation<br />
siRNAs <strong>and</strong> miRNAs are similar but form from different<br />
RNA precursors
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