BIO1140 Lecture 14: Transcription pt. 2

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BIO1140 B Dr. Caroline Petit-Turcotte
Transcription (Lecture) 02.27.2017-03.06.17
Learning Objectives:
Understand, describe and demonstrate the steps involved in transcribing DNA to mRNA
Be familiar with the elements comprised in a transcription initiation complex and its role
Explain and demonstrate RNA maturation and splicing
Compare and contrast RNA transcription in prokaryotes vs eukaryotes
Know, describe and/or compare the different elements of control for gene expression in prokaryotes vs eukaryotes
Activators, Repressors (enhancers, silencers), Alternative splicing, Operons
Regulation of Gene Expression control when certain genes are expressed, how long, and under what conditions
First level of regulation is the on/off switch to initiate transcription
Prokaryotes transcription, translation, gene expression all happen at once in the same area (no nuclear
membrane); regulation achieved through operons, additional genetic switches that control transcription (on/off)
operons: proteins that interact with DNA in specific areas to prevent or enable transcription
operator is a sequence on the DNA that is between the promoter and the gene itself; repressors bind to
operator and act as a physical block to prevent RNA polymerase from moving fwd on DNA sequence and
prevent transcription
o certain conditions in cell allows the repressor to be available, needs to be kept busy if not
needed to be used or used immediately after being made (transcribed and translated)
lac operon has 3 genes that are under the control of the operator and when translated; they lead to
beta-galactosidase, galactoside permease, and trans-acetylase they all breakdown lactose
o need all three genes interact with same repressor which needs to be inactivated by lactose for
transcription to occur to produce enzymes to manage remaining lactose in environment; when
o latose preset, e do’t eed those ezes, therefore repressor ind to operator to
prevent transcription of those genes
cyclic AMP operon
Eukaryotes after TBP bind to promoter region on DNA sequence, activators bind to enhancer sequences and
repressors bind to silencer sequences (proteins that bind to regulatory regions on genes); differences in gene
expression between individual cells depend on enhancers recognized by activators found only in specific cell types
genes all have TATA box proteins but have different combos of enhancers and repressor areas
o each cell will specifically make the proteins they need for those areas
i.e liver cells need albunin gene and will have lots of proteins to make activators to
epress alui gee ut does’t eed atiator proteis for rstali for les ell
in addition to TIC, activators and repressors control which genes are expressed and the rate at which
transcription occurs
posttranscriptional regulation determines how many mRNAs will go out of nucleus (not all of them make
it to translation) and how mRNA is spliced; RNA interference: silencing a gene
post-transcriptionally by miRNA or siRNA binding to part of the mRNA by
complementary base pairing
o I speifi ases, sall RNAs idig to 5’ UTR of other RNAs,
blocking translation
o Whe RNA is’t i proper oforatio, ezes will lead the
duplex to be degraded
o microRNA (miRNA) small strands of RNA from splicing entrons or
from intercoding regions that express miRNA; regulate the amount
of mRNA that stays available in the cell
transcribed like other RNA but its sequencing leads to
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