Protein Transport and Secretion Flashcards
proteins entering the er enter the ________ pathway
secretory
peroxisome v endosome v lysosome
peroxisome = break down fa's with oxygen endosome = formed from csm. transport of materials from golgi --> lysosome or vacuole. processing of internalized proteins. lysosome = digest viruses/bacteria. waste removal for cells.
function of the ER
post translational modification of proteins
protein destination is dependent on
location of the ribosome during translation:
by default ribosomes are
free, unless targetedti the endoplasmic reticulum
free ribosomes synthesize protein types:
Cytosolic proteins
Mitochondrial proteins
Nuclear proteins
Peroxisomal proteins
How do ribosomes get to the ER?
Most proteins that are destined for the ER are directed by an N-terminal ER signal sequence that binds the Signal recognition particle (SRP)
Approx 5-30 amino acids long, mainly charged residues
Explain the mechanism of SRP in facilitating ribosomes to the ER
- Translation begins
- SRP via signal sequence binds to ribsome . transaltion is paused.
- srp bound ribosom binds to SRP receptor on the RER membrane
- protein enters RER lumen via protein tranlocator on the RER membrane
- SRP recycled, translation proceeds with protein translocated into ER lumen
Smooth ER is site of ………..
site of lipid and lipid membrane biosynthesis
Function of ER
Assembly and folding of all transmembrane proteins.
Processing of proteins that are secreted by the cell or onwards to other organelles via the Golgi apparatus.
Site of post-translational modification of proteins e.g. N-linked glycosylation of precursor oligosaccharides
Disulphide bond formation
Error checking / Quality control:- Biosynthetic arrest of misfolded proteins
After processing in the ER proteins are delivered to the _____________.
Golgi apparatus.
Golgi apparatus structure
Stack of disc like membranes (Cisternae)
Cis or entry face.
Trans or exit face.
Functions of the Golgi apparatus
Proteins are sorted for delivery to other parts of the cell
Site of N-linked (amino acid aspargine) oligosaccharide modification - eg like adding an address to the protein
O-linked (amino acid pyrolisine) glycosylation
Oligosaccharide addition/modification acts as a recognition motif directing proteins to their appropriate destination in the cell.
Glycosylation is the process by which ………
……… a carbohydrate is covalently attached to a target macromolecule, typically proteins and lipids. This modification serves various functions eg acting as an address. In other cases, proteins are not stable unless they contain oligosaccharides linked at the amide nitrogen of certain asparagine residues.
How are proteins transported from the ER to the Golgi other organelles and into and out of the cell?
Process of vesicular transport
**Vesicular transport is also involved in the movement of proteins into and out of the cell - endocytosis and exocytosis.
Basic process of vesicular transport
Budding of organelle membrane. vesicle containing cargo protein. fusion of vesicle to target and release of cargo.
The process of vesicular transport is governed by
coated vesicle proteins
Three well characterised coated vesicles proteins are:
Clathrin: plasma membrane into endosomal and golgi compartments
COP-I: from golgi
COP-II: from ER to golgi
How is a clathrin vesicle formed?
1) coat of clathrin is assembled on the membrane. cargo proteins are selected from their cargo receptors.
2) bud is formed including clathrin, the receptors, the cargo proteins, and the membrane part itself.
3) vesicle is formed, from above constituents.
4) uncoating of clathrin, and naked vesicle moves to its location in the cytosol.
How can vesicle transport be highly selective?
- Rab proteins on cytosolic surface of vesicles directs specificity
- v-SNARE and t-SNARE mediate membrane fusion.
3 STEPS:
tethering
docking
fusion.
process of selectivity of vesicles by RAB
- Cargo vesicle = car
- protein = you
- RAB = tour guide
- t-SNARE on target membrane = your hotel
- v-SNARE = your hotel booking.
- RAB effector = receptionist at hotel, friend of Rab
so, you travel with v-SNARE and RAB in your cargo vesicle.
rab meets rab effector in the hotel, and you give v-SNARE to t-SNARE. Now you can enter the hotel i.e. target membrane.
Cytoskeleton - how does it help with cellular vesicular transport?
Microtubules: Components of the cytoskeleton also aid vesicular transport.
form long rope-like filaments - Important in maintaining cell structure.
Act as tracks guiding membrane vesicles to their correct destination. They have motor proteins on them
Aid ER to golgi transport.
