What happens when mRNA enters the cytosol? (SRP= signal recognition particle)
it docks to a ribosome ribosome starts translating the protein signal peptide at the N terminus of the secreted protein is immediately recognised as belonging to a secreted protein->ARP recognises signal peptide->helps it guide ribosome to ER mem
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Describe mRNA encoding soluble secreted proteins
Translated signal peptide is cleaved off by signal peptidase Native protein enters ER lumen for further processing
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Describe mRNA encoding ER membrane proteins
Translated signal peptide is cleaved off by signal peptidase ER membrane protein remains membrane bound for further processing
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How does hydrophobicity affect protein processing in the ER?
Hydrophobicity determines membrane association of ER membrane-localised proteins (Transmembrane domains are very hydrophobic )
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What is the role of tunicamycin (TM)?
blocks N-linked OS synthesis if you treat organisms with it they can no longer produce the oligosaccharide
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Why is N glycosylation important in protein processing in ER?
Step-wise removal of sugar residues as system to monitor the protein folding status N-glycosylation is important for proper protein folding (function)
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what is a control mechanism for protein folding and degredation?
step-wise removal of sugar residues
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Describe ER Quality Control system required for protein folding
protein enters ER->binds to SDF-BIP-ERDj3A complex (to ensure NO spontaneous folding)->brings it to CNX/CRT cycle-> binds to secreted protein & brings it into vicinity of PDI system which creates disulfide bridges->tertiary structure of a protein
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What is the physiological function of the ER?
Central organelle for protein synthesis in mammals&plants->1/3 of all proteins enter the secretory pathway; e.g. stress adaptive proteins and receptors->considered as a sensory organelle in plants
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How does the ER act as a stress sensory organelle?
Different set of receptors for biotic and abiotic stress which sense the stress and start signaling a lot of the stress needs to be secreted need to be folded at the ER if they are folded they are exported and help to relieve the stress
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What is the role of unfolded protein response (UPR)?
Enhance protein folding and export Remove unfolded proteins quickly Reduce translation
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What is IRE1? Under no ER stress?
transmembrane protein (exist as monomers when no ER stress
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What is IRE1? Under ER stress?
dimerise-> kinase domain which sits in cytosolic part of transmembrane protein-> autophosphorylation->allosterically activates RNase domain->binds mRNA->double loop->binds in pocket->splicing->RNA removed->plaque ends put together->mRNA coding for TF
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Alternative function of IRE1?
IRE1 alternatively splices mRNA of specific bZIP transcription factors
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bZIP28 function in ER stress signalling?
ER stress induces bZIP28 cleavage (S1P + S2P in Golgi apparatus) relocation to the nucleus to regulate UPR genes
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Activation of the Unfolded Protein Response (UPR)?
The UPR is activated by ER membrane-localised receptors partially developed by convergent evolution
SA (salicylic acid) – activtor of plant immunity.NPR1 – SA receptor.Psm ES4326 – bacterial pathogen of plants (NPR1 is a control because it is the siacilic acid receptor to acitvate immunity when you treat plants with siacilic acid)
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Example of how the ER participates in the establishment of symbiosis?
Abascule mychorriza goes to root and forms penetration organ ->nucleus goes to site where fungus is-> isotubules and ER form tube ->fungus penetrates the cell
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What actions of ER depend on stress severity?
UPR (mild ER stress):inductionofchaperones,Degradation of misfolded proteins,Attenuated translation. ER-PCD (programmed cell death:Severe / constant ER stress,ER swelling,Caspase-mediated apoptosis)
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Other cards in this set
Card 2
Front
Describe mRNA encoding soluble secreted proteins
Back
Translated signal peptide is cleaved off by signal peptidase Native protein enters ER lumen for further processing
Card 3
Front
Describe mRNA encoding ER membrane proteins
Back
Card 4
Front
How does hydrophobicity affect protein processing in the ER?
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