Week 10 - Protein Sorting Flashcards
What is the Endoplasmic reticulum
A vast network of tubules which extend throughout cytoplasm
What are the two types of endoplasmic reticulum
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
What are the functions of the SER
Lipid synthesis, hormone synthesis, Ca storage and detoxification
What are the functions of the RER
Site of protein synthesis and processing for transmembrane proteins as well as proteins secreted from the cell
Describe co translational translocation
Importing of proteins during translation, where no chaperone protein required due to the protein remaining in primary sequence as its attached to the ribosome as it enters ER
What conditions are needed for co translational translocation to occur
Recognised by Signal recognition particle
Recognised by ER and embedded within ER membrane
Describe the steps of recognition by an SRP
Signal sequence recognised on the N terminal of polypeptide, binds to that signal sequence and the ribosome.
What happens to the ribosome after translation
It’s released back into the free ribosome pool
What happens to the mRNA after translation
It is degraded
What are the two fates of a protein after it is made
Exocytosis via ER lumen
Become a membrane protein by being embedded in the ER membrane
What are the two ways a protein can be modified in the ER
Folding into its 3D conformation
Glycolysation
What is glycolysation
The addition of a sugar to a protein
What three things are glycolysation important for
Quality control
Recognition
Protection
How does glycolysation work
A precursor oligosaccharide (14 sugars) added to N terminus of protein as asparagine side chain during protein synthesis
How does quality control during glycolysation work
3 glucose removed from oligosaccharide, if folded, protein exits ER, if not glucosyl transferase + 1 glucose back on and then protein binds to calnexin to prevent agreggation, glucosyl transferase decides if protein is correctly folded
How does quality control affect continuously misfolded proteins
Unfolded protein response occurs and if problem continues, cell apoptosis
What are the three steps of the UPR
Inhibit protein synthesis
Degrade misfolded proteins
Increase transcription of chaperones
What are the names and roles of different receptors in the UPR
PERK: pausing translation
IRE1+AFT6: protein degradation and gene activation to increase protein folding activity
Describe pulse-chase experiments
Radiolabelled amino acids added to cell
All newly formed proteins are radio labelled
The cells then return to non radioactive medium after all new proteins have left the cell
What are the 3 types of vesicles and where are they located
COPII: ER
COPI: Golgi
Cathrin coated: plasma membrane and between Golgi and endosomes
What is Rab
A GTP binding protein and GTPase found on cytosilic surfaces of vesicles
When is Rab active and inactive
GDP bound is inactive (cytosol)
GTP bound is active (vesicle membrane)
What is responsible for activating Rab-GDP in the cytosol
GEF
What must happen for vesicular cargo to reach target organelle
The membrane must fuse using snare proteins
Describe membrane fusion
V-SNARE and T-SNARE wrap around eachother to form trans-SNARE complex and once close enough phospholipids can flow between them
Describe the Golgi apparatus
Flattened stacks of membrane enclosed departments (cisternae)
CIS face receives from ER
TRANS face secretes onwards
Describe conditions of the lysosome
Lots of enzymes to break macromolecules
Active at 4.5-5pH maintained by ATPase
Must be delivered via Golgi in clathrin coated vesicles
Describe an endosomes cycle
Late endosomes has meterial that’s been ingested by cell
Fuses with other endolysosomes or lysosomes generate endolysosomes
Once digestion complete they form lysosomes
What two things can happen to ingested material after an endocytotic vesicle fuses with an early endosomes
Degraded
Recycled
