11-ER

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How are proteins produced?
In the cytosol (these end up in the mitochondria/chloroplasts/ nucleus/ peroxisomes) Other proteins are secreted (secretory proteins) – enter and are translated at the ER (during translation, are imported into the ER)
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What makes it easier for a protein to cross a membrane?
The smaller the molecule & the more soluble in oil (hydrophobic, nonpolar) the more rapid it will diffuse across a membrane
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What can help molecules (bigger ones that strugle) cross the membrane?
Regulation of membrane potential Transporters & channels (pores) mediate protein / molecule delivery->more proteins across membrane at a lower conc of proteins (can be passive or active)
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How do transporters and channels work?
Proteins need a key (sorting signal) to enter-Proteins often use ligands in order to open transporters and channels to cross a membrane
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Describe protein sorting machine
Protein sorting starts with and after translation Targeting domains define destination Chaperones (e.g. HSP70) assist the transport to various organelles
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Describe the role of chaperones
Transporters/channels are small pores  a completely folded protein may be unable to cross  chaperones ensure protein gets through transporters and makes sure it does not start folding before it is in the organelle
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Describe protein import into organelles
e.g. Protein is recognized as being a chloroplast protein  is delivered into chloroplast  stromal targeting domain is cleaved off HSP60 chaperone then is involved in protein folding (if protein supposed to be in thylakoids inside chloroplast-2TDs
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Describe mitochondiral protein import
Targeting domain (presequence) of mitochondrial protein form positively charged amphipathic α-helices -> Mitochondrial protein sequence is polarized helps get it into the organelles
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Describe nuclear import
Import through nuclear pore complex. NLS is not cleaved off -proteins can reenter nucleus in case they are exported into the cytosol
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How does nucleus restrict nuclear import?
Nucleus has nuclear pores which restrict access to nucleus – large molecules like proteins cannot enter Pores consist of nuclear porins = gatekeepers
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How is the cargo adapted to support nuclear import?
Cargo e.g. TF – has nuclear localisation signal which helps doctor the importin to get them into nucleus
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Role of GAP in nuclear import?
activates importin (energy dependent process to get protein across pores into the nucleus)
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Role of GEF in nuclear import?
releases TF from the importin  importin binds to Ran-GTP and gets out of nucleus again
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What happens to nuclear locakisation signals after nuclear import?
not cleaved off because in some cases TF are oscillating (inside or outside the nucleus)–if outside they cannot transcribe->if genes no longer req->TF leave, NLS stays
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What are the 2 crucial functions ofthe ER?
Processing and delivery of secreted proteinsand Stress Integration
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Where are ribosomes?
on ROUGH ER, not smooth!
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What is the ER involved in?
Entry point into endomembrane system. Synthesis, processing and sorting of proteins. Anchoring sites for actin filaments-vesicular-/membrane trafficking
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How does the ER connect organelles across cells
It is a Continuous lumen connecting individual cells (connecting neighboring cells, and are also in physical contact with almost all organelles  can communicate with organelles and deliver what they need = supervises)
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Describe the ERs portein sorting machinery
Ribosomes translating proteins with a signal peptide move to ER ( rough ER) Sorting often requires multiple domains Integral membrane proteins do not enter ER lumen
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What is the secretory pathway?
secretion of soluble and extracellular matrix proteins. Proteins are correctly folded. A huge number of secretory and integral membrane proteins are glycoproteins->N-glycosylation in the ER->O-glycosylation in the Golgi
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What is SEC61?
required for translocation of proteins into ER lumen
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What are vacuolar proteins sorting genes?
> 40 vacuolar protein sorting (VPS) genes that are involved in protein sorting
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Describe vesicular transport
forwards and backwards between ER and Golgi-Forward / retrieval transport is mediated by different vesicles Vesicles can be distinguished by their surface(Vesicles have different coating (clathrin, COPI, COPII) depending on cargo&where ves. from)
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COPI coated vesicles? COPII?
backwards transport (some secretory proteins may need chaperones which need to be transported back to ER after they deliver to Golgi or transporting mistakes back to ER – rather than degrading – so they can be reused). COPII also from ER
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Clathrin coated vesicles?
Vesicles that bud off the PM/ where we see endocystosis = clathrin coated vesicles Vesicular protein sorting and loading of vesicles = clathirin coated vesicles
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Modifications in the Golgi apparatus crucial for proper delivery?
ER->phosphory of oligosaccharides on lysosomal protein. Removal of Man. Addition of GlcNAc. Addition of Gal, Addition of NANA. Sulfation of tyrosines and carbohydrates -> lysosome/PM/secretory vesicle
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Describe protein trafficking via the Golgi apparatus
Major protein sorting station. Cisternae of Golgi stacks differ in morphology->different enzyme set for specialised function. Products get processed from cis- to trans-cisternae before packaged into vesicles at the TGN-coat protein (COP) coats inv
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What are the 2 models for protein transport through Golgi?
Vesicular Transport Model (Evidence for specific receptors and vesicle coat proteins required) and Cisternal Maturation Model (Efficient retrograde transport of enzymes or de-novo synthesis required)
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Difference between consitutive and regulated secretory pathways?
Constitutive = housekeeping functions, proteins that are part of PM or lysosomes needed for cellular function – are processed constantly Regulated = proteins induced in response to stress
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Describe exocytosis
Secretory vesicles from the TGN fuse with PM and vesicle contents are released into the extracellular space
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Describe endocytosis
Endocytic pathway: PM invaginates, small vesicles bud off and move to the endosome
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Card 2

Front

What makes it easier for a protein to cross a membrane?

Back

The smaller the molecule & the more soluble in oil (hydrophobic, nonpolar) the more rapid it will diffuse across a membrane

Card 3

Front

What can help molecules (bigger ones that strugle) cross the membrane?

Back

Preview of the front of card 3

Card 4

Front

How do transporters and channels work?

Back

Preview of the front of card 4

Card 5

Front

Describe protein sorting machine

Back

Preview of the front of card 5
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