Endoplasmic Reticulum
- Created by: Amber Manley
- Created on: 11-01-14 11:39
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- Endoplasmic Reticulum and Golgi Apparatus
- endoplasmic reticulum
- appearance
- contiguous tubes and sacs
- er lumen (space) bounded by er membrane
- Rough ER
- ribosomes
- secretory proteins
- transmembranous proteins
- ER and golgi proteins
- production of secreted proteins
- mRNA coding for cytosolic proteins translated in cytocol
- by polyribosomes
- common pool of ribosomal subunits in cytosol
- mRNA encoding ER trageted protein translated by polyribosomes attached to membrane
- mRNA coding for cytosolic proteins translated in cytocol
- targeting protein production
- signal peptide binds to signal recognition particle, pauses translation
- hydrophobic amino acid
- SRP interacts with SRP receptor on ER membrane
- translation and passage through protein translocator in ER membrane
- SRP and SRP receptor recycled
- signal peptide binds to signal recognition particle, pauses translation
- soluble proteins
- translocator opens it's pore allows transfer of polypeptide chain across bilayer
- pore closes after protein completely transfered
- transmembranous proteins
- similar to soulube protein transfer, except contains a stop codon
- translocator discharges protein horizontally
- N-linked glycosylation
- precursor ogliosaccharride is assembled onto phosphodolicol
- transferred to peptide chain by enzyme
- ribosomes
- membrane synthesis
- phospholipid synthesis
- assembled in outer layer, by membrane bound enzymes
- scramblase (phospholipid translocator), causes layers to equilate
- Smooth ER
- no ribosomes
- transitional between er and golgi
- steroid hormone synthesis
- detoxification of drugs in the liver
- lipophilic drugs oxidised, increasing solubility
- may be further modified in cytosol before excretion
- appearance
- Sarcoplasmic reticulum
- calcium store in the muscles
- action potential depolarises membrane
- voltage gates open
- ca2+ enters cytosol
- stimulates muscle contraction
- ca2+ pumps restore levels
- Golgi Apparatus
- appearance
- stack of membrane bound compartments (cisternae)
- cis face is nearest the ER, vesicles from ER dock here
- trans face, vesicles depart for cell surface
- Functions
- secretory proteins sorted, modified and dispatched
- site of carbohydrate synthesis
- glycoproteins and proteoglycans
- prominant in secretory cells
- glycolysation
- protein marker
- protector
- cellular marker
- regulatory roles
- appearance
- Protein Folding
- 2 of 3 terminal glucose molecules rmoved
- calnexin is a chaperone molecule that recognises single glucose of incompletely folded protein, prevents export to golgi
- partialy folded proteins have another glucose added by glycosyl transferase, try again
- misfolded proteins are sent to cytoplasm for degradation
- correctly folded sent to golgi
- travel to golgi
- proteins need exit signals
- COPII interacts with cytosolic tails of receptor, causing a vesicle to bud off
- vesicles shed COPII coat and undetgo homolytic fission (join other vesicles)
- moves along microtubules to golgi
- travel from golgi
- vesicles coated in COPI bud from the golgi
- ER has proteins with retrieval signals that interact with COPI
- endoplasmic reticulum
- lysosomal proteins
- ribosomes
- secretory proteins
- transmembranous proteins
- ER and golgi proteins
- ribosomes
- hydrophobic signal moves horizontally, is degraded
- soluble proteins
- translocator opens it's pore allows transfer of polypeptide chain across bilayer
- pore closes after protein completely transfered
- soluble proteins
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