Name: Reena
Status: other
Grade: other
Location: Outside U.S.
Country: Pakistan
Date: Fall 2012
Question:
During transcription one of the two DNA strands becomes template strand.My question is what makes the template strand to be template strand. What about the non-template strand.
Replies:
Reena,
As you know, DNA has both a 'sense' strand and an 'anti-sense' strand
that is complementary to the sense strand. As you can imagine, when
DNA is transcribed to messenger RNA (mRNA), only one strand is used as
a template; to transcribe both strands would result in 50% of your
mRNAs coding for nonsense proteins. It does seem puzzling, though,
how RNA polymerase proteins can 'know' which strand to transcribe
during mRNA synthesis.
The answer lies in the way in which RNA polymerase is bound to the DNA
in the first place. RNA polymerase binds to what is called a promoter
region in the DNA upstream of the gene with the help of other proteins
called transcription factors. These proteins all bind to specific DNA
sequences, and their orientation is controlled by the geometry of the
binding and the promoter nucleotide sequence. Thus, the RNA
polymerase is oriented on the DNA strand by chemical bonds so that it
is in place to transcribe only the template strand and not its
complement.
Transcription and translation are both fantastically complex processes
that molecular biologists are continuing to learn more about and
understand. It's remarkable that given this complexity all of our
cellular machinery normally works!
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