Endoplasmic Reticulum and Golgi Flashcards
What do ‘chaperones’ do?
They mediate folding
Describe the process of docking to the ER.
Free floating ribosomes produce a signal peptide which binds to the signal recognition particle. The signal recognition particle binds to the signal recognition particle receptor on the ER membrane.
These docked ribosomes continue translation to synthesise transmembrane lumenal or secretory proteins
Describe the process of docking to the ER.
Free floating ribosomes produce a signal peptide which binds to the signal recognition particle. The signal recognition particle binds to the signal recognition particle receptor on the ER membrane.
These docked ribosomes continue translation to synthesise transmembrane lumenal or secretory proteins
SRP transferred to translocation channel, protein then synthesised into the lumen of the ER through the translocation channel.
Signal peptides cleaved by signal peptidase, releasing them into the ER lumen.
Describe how soluble secretory proteins translocate through the ER membrane.
- Signal peptide binds to signal recognition particle which binds to the signal recognition particle receptor.
- Ribosome translates through the translocation channel
- Once finished, cleavage of signal peptides by signal peptidase occurs.
- Mature soluble protein in the ER lumen.
Give an example of a chaperone (something that mediates folding) and what it does.
BiP is a chaperone which binds hydrophobic regions and prevents aggregation.
Describe the 3 processes that occur to ensure proteins are synthesised and folded correctly in the lumen of the ER.
- Chaperones such as BiP mediate folding and prevent aggregation (binding hydrophobic regions)
- Oligomeriasation (assembly of multi protein complexes)
- Disulphide bonds added by Protein Disulphide Isomerase.
Describe how integral membrane proteins translocate through the ER membrane.
- Single pass
- Multipass
- Signal peptide binds to signal recognition particle which binds to the signal recognition particle receptor.
- Ribosome translates through the translocation channel.
-Integral membrane origins have “start” or “stop” transfer sequences which re hydrophobic sequences that remain in the membrane.
>Number of internal hydrophobic transfer sequences determines the number of membrane domains
- Multipass Proteins use an internal signal sequence so there are two hydrophobic sequences embedded in the protein.
Then, further along the protien, there are more stop and start transfer sequences that embed themselves in the protein. (Stitched into the lipid bilayer as they are synthesised).
At which terminal is the signal sequence located?
N terminus
What is a type I single pass integral membrane protein?
A single pass protein with its C terminus on the cytosolic side and N terminus on lumenal side.
What is a type II and type III integral membrane protein?
Single pass proteins
II N terminus in cytosol
III C terminus in cytosol
II- Signal sequence proceeded by positive amino acid side chains
III -positive amino acid side chains after signal sequence
What are type IV integral membrane proteins?
Multipass Membrane proteins
Which terminus are proteins glycosylated at and why does this occur?
- N linked glycosylation
- Makes them more hydrophilic and prevents aggregation
- Protects from degradation.
What is the function of the smooth ER?
Synthesis of lipids and steroids.
What is retrograde and anterograde trafficking?
- Retrograde- towards ER
- Anterograde- away from ER
What is the role of clathrin?
Forms a coat around proteins that are about to be endocytosed.
It attaches to the membrane via an adaptor. The cage structure causes curvature of the membrane and budding off until a vesicle is formed.
What is the structure of clathrin?
Three ‘legged’ triskelion which can form a cage
How is the endocytotic vesicle released after clathrin cage has formed budding off vesicle?
Released by dynamin which forms a collar around the budded off section
What is cisternal progression?
Instead of vesicles budding off, proteins are moved by the cisternal sacs moving forward and vesicles merging to replace them as they move forward.
Which protein coats drive transport in the forward and retrograde directions?
- Forward direction is driven by COPII
- Retrograde direction driven by COPI
What is meant by cis, medial and trans golgi?
Cis- golgi closest to ER
Medial-middle stacks
-Trans- furthest stack from the ER
What are snares and what do they do? What are V and T snares?
Proteins that are unstructured until they bind to each other.
V snares are on the vesicle and T snares are on the golgi membranes.
They bring two membranes in close proximity to bind
They enable TARGETING.
