Page 47 - Cell biology PDG 2024

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DNA transcription

Transcription is the copying the genetic information from
DNA to RNA. It is carried out by an enzyme called RNA
polymerase and a number of accessory proteins called
transcription factors (proteins that control the rate of
transcription)

Transcription factors has the ability to bind to specific DNA
sequences called enhancer and promoter sequences (which indicates
the starting point of transcription) in order to recruit RNA polymerase
to an appropriate transcription site.

Together, the transcription factors and RNA polymerase form a
complex called the transcription initiation complex.

Once the transcription initiation complex binds to the promotor
sequence, RNA polymerase unwinds a portion of the DNA double
helix, exposing the bases on each of the two DNA strands.

Note that: The transcription complex initiates transcription, and the
RNA polymerase begins mRNA synthesis by matching
complementary bases to the original DNA strand (A to U, T to A, C to
G and G to C). RNA polymerase then catalyzes the formation of
phosphodiester bonds between adjacent ribonucleotides.

The mRNA molecule is elongated and, once the strand is completely
synthesized, transcription is terminated when the RNA polymerase
finds a stop sequence.

This mRNA then exits the nucleus to be translated into proteins by
means of ribosomes found in the cytoplasm.

Pre-translational mRNA processing

The mRNA which has been transcribed up to this point is referred to
as pre-mRNA so processing must occur to convert it into mature
mRNA. The processing includes:

 5′ Capping

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