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Chapter 7.1

BIO206H5 Chapter Notes - Chapter 7.1: Tata Box, Sigma Factor, Ribonucleoside

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George S Espie

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Flow of information from DNA to RNA to protein - central dogma of
molecular biology
Cells can synthesis large amounts of protein whenever necessary
Ribonucleotides - sugar ribose
Contains uracil not thymine
Single stranded - fold variety of shapes, carry out functions in cells
RNA - linear polymer of four different nucleotides linked by phosphodiester bonds
RNA chain determined by complementary base-paring with DNA template
Ribonucleotides are added in enzymatically catalyzed reactions
Does not form hydrogen bonds with DNA template strand
Copied from a limited region of DNA, few thousand nucleotides long
catalyze formation of phosphodiester bonds
Unwinds DNA
Uses ribonucleoside triphosphates for energy
Can start without primer - not as accurate as DNA, mistake every 10^4 nucleotides
RNA polymerase
Synthesis of the next RNA starts before the previous one is finished
Transcription produces RNA complementary to one strand of DNA
Eukaryotes mRNA carry info transcribed for one gene, single protein
Prokaryotes carry for several different proteins
Nonmessenger RNAs act as regulatory, structural, and enzymatic components, play key
parts in translation of protein
Gene expression is the process of translating DNA to a product that has effect on cell
Several types of RNA are produced in cells
RNA polymerase collides with DNA then binds firmly when promoter is detected, then
opens helix, elongates, then encounters terminator, releases DNA and newly made RNA
disengages after 10 nucleotides
Binds with RNA polymerase after termination
Subunit, Sigma factor recognise promoter
Promoter is asymmetrical , one orientation
Signals in DNA tell RNA polymerase where to start and finish
Has three different RNA polymerases, RNA polymerase II -> mRNA
RNA polymerase requires accessory proteins, general transcription factors (GTF)
DNA in eukaryotes are packet into chromatin structure
Initiation of eukaryotic gene transcription is a complex process
RNA polymerase cannot initiate transcription in vitro
TFIID binds to TATA box (25 nucleotides upstream), causes distortion
Other factors then pile on to complete the transcription initiation complex
Adding phosphate groups to tail of RNA polymerase by TFIIH, disengages polymerase from
the GTFs
Eukaryotic RNA polymerase requires general transcription factors
RNA processing is needed before it exits the nucleus
RNA capping 5', guanine with methyl group, after 25 nucleotides made
Polyadenylation 3', first trimmed, then add hundreds of adenine nucleotides, Poly-A
mRNA processing:
Eukaryotic RNAs are transcribed and processed simultaneously in the nucleus
From DNA to RNA
8:45 AM
Ch 7.1 Page 1
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