Compartments and Protein Sorting (ch 12) Flashcards
(71 cards)
At what stage of protein translation does the signal recognition particle (SRP) recognize the emerging protein?
The SRP goes partially into the ribosome tunnel to scan the protein before it even emerges.
What are the 4 distinct intracellular compartment families?
- Nucleus + cytosol
- All secretory+endocytic organelles
- Mitochondria
- Plastids
What are the 3 distinct protein transport pathways?
- Gated Transport (cytosol>nucleus)
- Transmembrane transport (>ER)
- Vesicular transport (secretory transport)
What is the purpose of a protein signal sequence?
An “address” for proteins. Can be hydrophilic/phobic, polar/non-polar, -ve/+ve charge. Just something recognizable.
In folded protein, signal sequence is on ______. In unfolded protein, signal sequence is on ______.
Folded: protein surface
Unfolded: N-terminus
Does most protein transport occur while the protein is folded or unfolded?
Unfolded.
What end of the protein enters the ER initially? What about if the protein has to re-enter the ER after leaving?
Enter initially: N-terminus
Re-enter: C-terminus
Where would you expect to find shorter proteins? What about longer ones?
Shorter: in cytosol, lost signal sequence
Longer: in transit to other locations
What is transported into the nucleus through the nuclear pore complexes?
Only mRNA and transcription factors.
At what rate are molecules transported into and out of the nucleus?
~500 molecules per second!
How does the nuclear membrane bend around the nuclear pore complexes?
With the help of membrane ring proteins and nuclear basket proteins which distort the membrane.
How many different proteins make up a nuclear pore complex?
~30 different proteins.
How are large molecules excluded from the nucleus by the nuclear pore complexes?
Because of the channel nucleoporins which project into the opening and filter away large molecules but allow small ones to pass.
What is the function of nuclear import receptors?
To enable the movement of cargo proteins into the nucleus when directly bound to the receptor or indirectly through an adaptor protein.
Does changing one amino acid on a nuclear localization signal affect the import of a protein?
It can. Sometimes resulting in aggregation and no transport.
How do nuclear import receptors carry cargo through the nuclear pore complex?
By attaching to FG repeats on nucleoporins and “hopping” through the channel.
How is a monomeric GTPase activated? By what?
Guanine exchange factor (GEF) replaces GDP on inactive GTPase with GTP to activate.
How is a monomeric GTPase inactivated? By what?
GTPase activating protein (GAP) removes a phosphate from GTPase-bound GTP, converting it to GDP and inactivating the GTPase.
What is the name for the monomeric GTPase involved in transport across the nuclear pore?
Ran-GTP and Ran-GDP depending on localization and activation status.
What mechanism imposes transport directionality through the nuclear pore?
The activation/inactivation of Ran-GDP/GTP.
How is Ran-GDP activated as it enters the nucleus? By what?
Ran-GEF replaces Ran-bound GDP with GTP, activating Ran.
How is Ran-GTP deactivated as it exits the nucleus? By what?
Ran-GAP converts Ran-bound GTP to GDP, deactivating Ran.
How does Ran-GTP assist nuclear import receptors to transport proteins into the nucleus?
Ran-GTP replaces cargo protein by binding to nuclear import protein, releasing the cargo into the nucleus. The import protein with bound Ran-GTP then exits the nucleus.
How does Ran-GTP assist nuclear export receptors to transport proteins out of the nucleus?
Binds to export receptor in nucleus, causing it to pick up the cargo protein and take it out of the nucleus. Ran-GDP and cargo both release once in the cytosol.
