BIOLOGY 1A Lecture Notes - Lecture 21: Sigma Factor, Spore, Helicase
Lecture 20 Review:
SNP can be any change in the DNA
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A locus can have multiple different SNPs; gene A can have many different
mutations
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Central Dogma: info in DNA is replicated then transcribed into RNA then translated
into proteins
Prokaryotic:
The gene has a promotor and open reading frames (multiple) transcribed as one
single unit
Not seeing the multiple frames transcribed at once in euk
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Polymerase makes factors of DNA and starts because of promoter
Promoter has -35 bp and -10 bp
-35 bp has the sigma factor which tells polymerase what to do
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-10 has the RNA polymerase which makes RNA
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Bacterial RNA polymerase: Mike Chamberlain
Has multiple subunits to make it functional, 2 alpha, beta, beta' and sigma
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Sigma factor is at -35
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It has not opened up yet. We had to pop open DNA but in RNA there is no
helicase; the polymerase does it itself
We copy DNA into a single stranded RNA
So we replace the 2 'OH to make the RNA unstable so we can
turn it on and off bc it is unstable
If its stable we cant get rid of it
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Uracil replaces thymine
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No primer when transcription starts the RNA polymerase just
begins
Unlike DNA which hhad RNA primer
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Synthesis is 5' to 3'
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There is a variety of sigma factors in order to regulate. Such as for heat or
sporulating
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It follows template strand and copies what is on coding strand
Transcribes gene
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RNA polymerase only does 60 NT/sec whereas DNA does 1000 NT/sec
Because… it does not have helicase to unwind DNA and it has the
long RNA molecule behind it resulting in steric hindrance
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Energy comes from cleavage of the diphosphate moleucle
Propels it through helicase
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How do you know where sigma binds?
Set up experiment: have DNA molecule have a protein land on it.
Deduce where it will bind to it
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Make last nucleotide radioactive to follow it
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Add enzyme that cuts at every base pair- won't cut around the
protein (can't see it)
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How to STOP the sequence:
CO TRANSLATIONAL TRANSCRIPTION
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A sequence in RNA is a stop sequence then it forms a loop. The Rho
protein recognizes it and binds to it and it sends a signal to the
polymerase to stop.
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Eukaryotes:
Three polymerases
Pol 1 is for reparation; Pol 3 is the one that synthesizes
snRNA and siRNA are discovered by Andy Fire and Pol 2/3
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There is no cotranslational transcriotion
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No free 5' end. In transcription with bacterial RNA there was a first nucleotide
and the 3' OH attacked the 5' phosphate which left 5' phosphate hanging out
which made it unstable
Eukaryotes put a GTP molecule backwards on the free 5' phosphate so
that there is phosphate-phosphate to increase stability of eukaryotic
message
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End of gene was susceptible to being degraded so added Poly AAA sequence
Adds 150 AAAAAA
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Introns and Exons
Exon is not cut out
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Introns are cut out ( loops in experiment )
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TOM CECH> rna splicing
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Machinery:
snRNA bind to boundaries and the splicing factors splice then it is
religated
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Lecture 21-3/9
Tuesday, March 13, 2018
12:59 PM
Document Summary
Snp can be any change in the dna. A locus can have multiple different snps; gene a can have many different mutations. Central dogma: info in dna is replicated then transcribed into rna then translated into proteins. The gene has a promotor and open reading frames (multiple) transcribed as one single unit. Not seeing the multiple frames transcribed at once in euk. Polymerase makes factors of dna and starts because of promoter. 35 bp has the sigma factor which tells polymerase what to do. 10 has the rna polymerase which makes rna. Has multiple subunits to make it functional, 2 alpha, beta, beta" and sigma. We had to pop open dna but in rna there is no helicase; the polymerase does it itself. We copy dna into a single stranded rna. So we replace the 2 "oh to make the rna unstable so we can turn it on and off bc it is unstable.
