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32 Cards in this Set
- Front
- Back
What are TSF's regulated by what b/c of changes in TSF's?
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Regulated in response to environmental factors
Signal transduction pathways result in changes in gene expression b/c of changes in TSF's |
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Describe the characteristics of DNA methylation
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Some genes controlled this way
Assocoated with heritable gene inactivation Required for X chromosome inactivation Methylation usually occurs at a ceratin stage of development and/or tissues Active promotors CANNOT by methylated and methylated promotors CANNOT be activated Methyl C recruit chromatin and HDAC's to shut off tanscription completely |
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What are some important things about CpG islands?
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C-G rich areas
Often at the 5' end of housekeeping genes which are normally not methylated Inappropriate methylation of CpG islands in tummor suppresspr genes and/or genes encoing protein involved in apoptosis has been associated with some cancers |
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Alternative Sploicing and/or Polydenylation
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Important for getting more then one protein from one mRNA
Major reason have few gens but many proteins |
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Constituitive Alternative Splicing
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Not particulary regulated, not specific
Several version of a protein may be made in the same cell at the same time Results from sequence at exon/intron borders dont conform prefectly to consensus makeing it more difficult for snRNP's to recognize |
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Regulated Alternative Splicing
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More specific usually a tissue specific or developmental specific regulation
Addition or removal of a functional domain Single cell will express only one version of teh protein at any given time |
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What are the different ways that alternative splicing can result in different proteins?
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Optional Exon
Optional Intron Mutually exclusive exons Internal splice site |
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What are one of the ways you can regulate proteins?
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Regulated the stability of mRNA which is sometimes faster that regulating at the transcritional level (no waiting for TSF's)
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Describe the usual/defualt pathway for mRNA degradation
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Shortening or removal of the poly A tail (deadenylation)
This leads to decay in 3' - 5' direction Also can cause Decapping 5' end which can lead to decay |
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Decapping Pathway
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Less common
Decapping starts first and you have degradation mostly from 5' end |
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Endonucleolytic Pathway
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Less Common
Signal for endonuclease and lose PolA tail all at once whic triggers degradation for the 3' end |
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RNA Surveilance (nonsense)
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Process by which aberrant transcripts (defective mRNA's)are rapidly degraded with out being deadenylated first
Can Detect: Early nonsense codons, unsplced intron and extended 3' UTR |
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What does the regulation of mRNA stability depnds on?
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Depnds on sequeces in 3' UTR that increase or inhibit degradation
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What happens when iron levels are low?
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Endonucleolytic cleavage of mRNA is blocked which stabilizes the mRNA so more protein can be translated
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What do both miRNA and siRNA do?
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Both bind to target sites in the 3' UTR of target mRNA and inhibit protein synthesis
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miRNA
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Binds to sequences that are NOT compleatly complementary
One can regulate many mRNA's If an mRNA has more then one are sequester in P bodies therefore not translated and eventually degraded Important in cell growth and development |
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siRNA's
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Bind to sequences that are perfectly complementary
Cause mRNA cleavage and rapid degradation Protection of cell from viral infection |
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RNA editing
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Rare mechanism to alter the sequence of mRNA after transcription
Editing of apolipoprotein B |
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Translation Regulation
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Faster protein adjuestment then transcriptional
Short-term protein regulation Important for developemtnal regulation RBC's almost exclusively b/c no nucleus Intiation is the rate limiting step and site of most regulation |
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Accessibility of 5' cap Initiation of Translation
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Proteins that stabilize structures in the 5' UTR can repress translation by making the cap structure less accessible to cap-binding protein
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Phosphorylation of eIF-2-GDP
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Prevents formation of eIF-2-GTP
Overall inhibition of translational initiation and protein synthesis |
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What can 3' UTR sequeces do for mRNA?
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Direct the mRNA to regions of the cell where translation is more or less likely to occur
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Masking
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Occurs during gametogensis
mRNA's sequestered and stored for later 3' UTR are required for unmasking |
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Two places protein can be synthesized
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On "free" ribosomes in the cytosol
"Membranous"ribosomes bound to the ER |
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Proteins made on free ribosomes
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Default=stay in cytosol
Signal for protein to go to mitochondria or nucleus Post-Translational Tanslocation |
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Proteins made in the ER
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Default = secretion
Co-translational translocation Localization depends on signals provided by glycosylation patterns |
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Protein Folding
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Occurs in ER lumen
Chaperones and Chaperonins Mild folding varients can usually be controlled but those prone to aggregation can cause problems |
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Chaperone Proteins
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Bind and stabilie unfolded or partially folded proteins
Preventing degradation ot aggregation |
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Chaperonin Proteins
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Directly faciliate the folding of proteins
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Proteasomes
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Degrade most misfolded proteins
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I-Cell Disease
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Patients are unable to phosphoraylate the mannose.
Results in protein being secreted instead of localized |
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Proteasome
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Degradation occurs
Found in cytosol Contineous or regulated Cell to be degraded must have Ubiquitin |