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Biology > Control of Eukaryotic Gene Expression > Flashcards

Control of Eukaryotic Gene Expression Flashcards

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1
Q

Regulation of gene expression at CHROMATIN level

A
  • histone modification

- DNA methylation

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2
Q

Histone Acetylation

A
  • histone acetyltransferases (HATs) add acetyl groups to positively-charged lysine residues on N-termini of histone tails; neutralise charges
  • reduce electrostatic attraction between DNA and histones
  • chromatin decondenses, increasing access to RNA polmerase and transcriptional machinery
  • increase transcription
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3
Q

Histone Deacetylation

A
  • histone deacetylases (HDACs) remove acetyl groups added by HATs
  • increase electrostatic attraction between DNA and histones
  • chromatin condenses to default condensed state, decreasing access to RNA polymerase and transcriptional machinery
  • decreases transcription
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4
Q

DNA methylation

A
  • DNA methlytransferases add methyl groups to cytosine residues in CpG islands
  • chromatin condenses, decreasing access to RNA polymerase and transcriptional machinery

1) Methyl groups prevent transcriptional proteins from binding to promoter
2) Methyl-CpG- binding proteins recruit additional proteins (e.g HDACs) that suppress transcription

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5
Q

Regulation of gene expression at TRANSCRIPTIONAL level

A
  • Control elements (promoter, enhancers, silencers)

- Proteins (TFs)

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6
Q

Role of promoters in regulating gene expression

A
  • mediate binding of basal transcription factors and RNA polymerase to transcription start site, thereby allowing transcription to begin
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7
Q

Role of enhancers in regulating gene expression

A
  • mediate binding of activators (specific TFs) and thus help to from transcription initiation complex
  • increase rate of transcription
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8
Q

Role of silencers in regulating gene expression

A
  • mediate binding of repressors (specific TFs) and thus help to from transcription initiation complex
  • decrease rate of transcription
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9
Q

Properties of DISTAL control elements

A
  • act over relatively long distances
  • function independent of orientation
  • function independent of position
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10
Q

Role of general/basal TFs in regulating gene expression

A
  • TFIID 1st to bind to promoter; TATA binding protein recognises TATA box
  • binding changes its own as well as DNA conformation
  • mediates binding of other TFs before RNA polymerase binds to form transcription initiation complex
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11
Q

Role of specific TFs in regulating gene expression

A
  • bind to respective distal control elements, influencing rate of transcription
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12
Q

Regulation of gene expression at POST-TRANSCRIPTIONAL level

A
  • 5’ capping (7-methylguanosine cap)
  • polyadenylation (addition of 3’ poly(A) tail)
  • RNA splicing (introns excised, exons spliced together)
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13
Q

Functions of 5’ 7-methylguanosine cap

A
  • prevent growing primary mRNA chain from being degraded by ribonucleases, RNAses
  • facilitate export of mRNA from nucleus to cytoplasm
  • recognition of mRNA by ribosomes for translation
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14
Q

Polyadenylation process

A
  • cleavage recognise poly(A) signal sequence and bind to it
  • pre-mRNA bends, stabilised by stabilising factors
  • endonuclease recognises poly(A) signal and cuts downstream at the 3’ untranslated region
  • poly(A) polymerase synthesises poly(A) tail by adding long sequence of adenine nucleotides at the 3’ end
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15
Q

Functions of poly(A) tail

A
  • prevent pre-mRNA from being degraded by ribonucleases, RNAses
  • facilitate export of mRNA from nucleus to cytoplasm
  • recognition of mRNA by ribosomes for translation
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16
Q

RNA splicing process

A
  • small nuclear RNAs (snRNAs) associate with other proteins to form small ribonucleoproteins (snRNPs)
  • snRNPs associate with other proteins to form spliceosome
  • within spliceosome, snRNAs base pair with nucleotides at splice sites along introns
  • spliceosome cleaves pre-mRNA at 5’ splice site and intron is joined to branch point within it
  • then cleaved at 3’ splice site, removing intron as lariat-like structure, while exons spliced together
  • continues till all introns removed and exons spliced together
  • spliceosome dissociates and mature mRNA is released
17
Q

Regulation of gene expression at TRANSLATIONAL level

A
  • half-life of mRNA

- initiation of translation

18
Q

Regulation of half-life of mRNA

A

1) mRNA degradation
- once mature mRNA enters cytosol, exonucleases shorten poly(A) tails to critical lengths
- 5’ 7-methylguanosine caps removed by decapping enzymes and mRNA is degraded

2) destabilising elements

19
Q

Regulation of initiation of translation

A

1) binding of regulatory proteins at 5’ UTR
- regulatory proteins bind to 5’ untranslated region of the mRNA, preventing binding of small ribosomal subunit to 5’ cap and thus ribosomes

2) length of poly(A) tail
- some mRNAs lack poly(A) tails that are long enough to initiate translation

3) binding of regulatory proteins at 3’ UTR
- regulatory proteins bind to 3’ untranslated region of the mRNA, protecting mRNA from being degraded by degradative enzymes, allowing translation to proceed

4) global initiation
- involves activation/inactivation of one or more protein factors (e.g translation initiation factors, eukaryotic initiation factors that promote proper association of ribosomes to mRNA, phosphorylation of ribosomal initiation facotrs) required to initiate translation

20
Q

Regulation of gene expression at POST-TRANSLATIONAL level

A
  • biochemical modifications

- protein degradation

21
Q

Regulation of biochemical modifications

A
  • glycosylation; additon of short chain carbohydrates (oligosaccharides) to proteins
  • phosphorylation; reversible addition of phosphate groups by kinases (removal by phosphatases)
22
Q

Regulation of protein degradation

A
  • length of time each protein functions is regulated by selective degradation
  • cell attaches molecules of small protein, ubiquitin, to proteins
  • marks them for degradation when proteasome recognises ubiquitin-tagged protein

Biology (14 decks)

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