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Flashcards in control of gene expression 2 Deck (25):
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control of eukaryotic transcriptional initiation

  • activator proteins bind upstream the enhancer sequence and active the basal transcription complex
  • multiple epigenetic mechanisms control gene expression via local chromatin condensation: histone modification and in vertebras' direct DNA methylation on cytosine helps maintain patterns of gene repression in some somatic cells

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multiple epigenetic mechanisms control gene expression via local chromatin condensation:

histone modification and in vertebras' direct DNA methylation on cytosine helps maintain patterns of gene repression in some somatic cells

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around 95% of human genes show..

alternative splicing -introns ar removed from pre-mRNA

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RNA editing

-post transcriptional editing increases e.g. alternative splicing

increases the number of distinct proteins that can be encoded in a genome

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in vivo modification of mRNA

-splitting of mRNA -addition of uridine to mRNA -deletion of uridine from mRNA

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in different tissues..

diff alternative splicing will occur

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what regulated alternative splicing

repressors and activators e.g. if activator is present then the intron will be spliced

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miRNA

microRNA -small-non coding RNA molecules -22 nucleotides -function in RNA silencing and post transcriptional regulation of gene expression

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microRNA role is to

specifically regulate gene expression -key in biological processes such as development, cell birth and death and cancer

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how to miRNA regulate gene expression

by blocking translation of specific mRNAs and cause their degradation

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RNAi

RNA interference -double stranded -a biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules

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where are RNAi found in nature

yeast, bacteria, the mouse and fruit fly

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model organisms

great for experiments because: share with humans many genes and key biochemical and physiological functions that have been conserved by evolution

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andrew fire and craig mellow and their discovery on RNAi

-injecting double stranded RNA reduced expression of specific genes -it does this by reducing levels of mRNA -this RNA interference is sequence specific

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siRNA

small interfering RNA

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siRNA and gene control

regulates gene expression by blocking translation of specific mRNAs and cause their degradation

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what can RNAi act as

a defence mechanism against dsRNA viruses and transposable elements

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RNAi and worm

1.e.coli, expressing double stranded RNA, eaten by worm 2.double stranded RNA injected into gut

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fate of target RNA silenced by RNAi

1. cleavage of target RNA 2.translation repression and eventual destruction 3. formation of heterochromatin on DNA fro which target RNA is being transcribed

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UTRs (untranslated regions) can control...

mRNA stability

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control stability- cytosolic aconitase and transferrin receptors

Without Iron

  • cytosolic acontase is complimentary to the transferrin receptor mRNA
  • this means the mRNA is stable and can be translate
  • iron uptake into cell

with excess iron

  • iron is complementary to part of the cytosolic aconitase
  • this changes the shape of the cytosolic acontaise so it can no longer fit onto the transferrin mRNA
  • thereofore mRNA is not stable and no transferrin receptors will be translated for and no iron will be uptake

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control of translation- ferritin translation

-Ferritin is a blood cell protein that contains iron

No iron present

  • cytosolic aconitase can fit onto the transferrin mRNA
  • translation is blocked
  • no ferritin made

Excess iron

  • iron is complementary to cytosolic aconitase and changes its configuration
  • will no longer fit onto the ferritin mRNA
  • therefore ferritin mRNA will be translated
  • iron bound within cell

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types of RNAi

-all double stranded and cause the translation of mRNA to be reduced without damaging actual DNA

dsRNA cleavage.

MicroRNA.

Three prime untranslated regions and microRNAs.

RISC activation and catalysis.

siRNA

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miRNA processing and mechanism of action

  1. pri-miRNA is cleaved 
  2. leaves the nucleus via special pores
  3. pre-miRNA is diced by a dicer making it single stranded
  4. associates with argonaute and othe rrpoteins and forms a RISC molecules (RNA induced silencing complex)
  5. causes rapid degradation by slciing mRNA
  6. unable to be translated and therefore degraded 

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