DNA/RNA Metabolism

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DNA/RNA Metabolism
Blackburn Gait, Ch. 6 and 7 Transcription
understand components of transcription bubble
know the importance of promoter sequences in
proks/euks know how nucleic acid structure
affects transcription termination (both Rho-dep
and Rho-indep) know an example of activator and
repressor of transcription know what
transcriptional enhancer elements also called UAS
(upstream activator sequence) do and their mode
of action understand attenuation RNA
Processing understand 5-capping reaction and
reason for cap understand 3-endonuclease
cleavage and polyadenylation and reason for
A-tail know steps in RNA splicing and
alternative splicing
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DNA metabolism
Replication DNA replication - process of copying
genetic information DNA acts as a template for
replication and transmission of genetic info One
strand is the complement of the other
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DNA metabolism
Stages of Replication Elongation
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DNA metabolism
Stages of Replication Elongation
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DNA metabolism
Stages of Replication Elongation
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DNA metabolism
Telomeres
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DNA metabolism
Telomeres
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DNA metabolism
Telomerase
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DNA metabolism
Telomerase
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RNA Metabolism
Transcription - uses DNA-dependent RNA
polymerase Polymerization is asymmetric - only
one strand of DNA used as template, new RNA chain
is identical in sequence to the nontemplate
strand
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RNA Metabolism
Transcription RNA synthesis initiated at
promoters (specific DNA sequence) Typical E.Coli
promoters
Pribnow box
EUKARYOTES
-25 TATA box (TATAAA)
-75 CAAT box
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RNA Metabolism
Transcription - termination Termination sites
have a palindromic sequence just prior to
termination point and RNA transcribed has short
inverted repeats (GC-rich regions) which form
hairpin GC-rich regions followed by 4-10 AT
bp Stem-loop structure in RNA being synthesized
induces pausing of RNAP Weak UA bp cause a
conformational change in RNAP and RNA breaks free
of DNA Rho-independent termination
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RNA Metabolism
Transcription - termination Rho-independent
termination
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RNA Metabolism
Transcription - termination Rho-dependent
termination Also get hairpin formed but not G-C
rich and no uridines after it Special protein
Rho is needed for termination Rho may bind 5-end
of nascent RNA and travel along behind RNAP Rho
may then interact with b-subunit of RNAP and stop
transcription RHO may be a helicase and unwind
the RNA from the RNA-DNA hybrid
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RNA Metabolism
Transcription - frequency of transcription
regulated by inhibitors (repressors) and
activators of RNAP Repressor trp
repressor Activator CAP (catabolite activator
protein)
Trp dimer HTH motif
Trp
DNA
DNA
Interacts with RNAP
CAP dimer (HTH motif)
cAMP
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RNA Metabolism
Transcription Transcriptional enhancer elements
also called UAS (upstream activator sequence) If
a UAS is deleted it abolishes promoter activity
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RNA Metabolism
Transcription Transcriptional enhancer elements
also called UAS (upstream activator
sequence) Enhancer function independent of
orientation or distance from affected gene
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RNA Metabolism
Transcription Transcriptional enhancer elements
also called UAS (upstream activator
sequence) Models for action of enhancers
Enhancer box is entry site, pro binds and then
migrates along DNA in order to interact with RNAP
Loop out DNA
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RNA Metabolism
Transcription Transcriptional enhancer elements
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RNA Metabolism
Transcription Transcriptional enhancer elements
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RNA Metabolism
Transcription Transcriptional enhancer elements
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Attenuation (prokaryotes)
Attenuation is means of controlling
transcription of a particular mRNA through the
formation of translation-dependent alternative
RNA structures For example, expression of the
operon that encodes proteins required for
tryptophan biosynthesis is modulated based on
supply and demand for tryptophan A short open
reading frame that encodes tryptophan, and a
downstream RNA region (the attenuator) are key
element of control
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Attenuation (prokaryotes)
Co-transcriptional translation determines what
structure the attenuator RNA will adopt
Abundant supply of tryptophan and movement of
the ribosome promotes a structure that terminates
transcription Stalling of ribosome due to lack
of tryptophan promotes a structure that prevents
termination
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RNA processing
Proks vs. Euks In proks, transcription
translation coupled In euks, processes are
temporally spatially separated so more control
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RNA processing
mRNA processing 5-capping 3-endonuclease
cleavage and polyadenylation RNA splicing
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RNA processing
mRNA processing 5-capping
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RNA processing
mRNA processing 3-endonuclease cleavage
polyadenylation
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RNA processing
mRNA processing RNA splicing editing
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RNA processing
mRNA processing RNA splicing editing
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RNA processing
Alternative splicing
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RNA processing
Alternative splicing
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