Flashcards in Intracellular Compartments and Protein Sorting: Part 1 Deck (35):
What is an organelle?
a subcellular compartment or large macromolecular complex, often membrane-enclosed, that has a distinct structure, composition and function
What kind of ER do the liver and pancreatic cell need?
liver- needs more smooth ER to break down toxic components (detoxify)
pancreatic-needs more rough ER to make secretory proteins
What two components are exchanged between intracellular compartments?
lipids and proteins (dynamic; change over time)
What are five main components of the endomembrane system?
4. Golgi apparatus
What are the two different pathways in the endomembrane system called? Describe them.
1. Biosynthetic/Secretory pathways:
a)biosynthesis: proteins and lipids made in the ER delivered to the membranes of other organelles
b)secretion: secreted proteins; contents move OUT of cell (exocytosis)
2. Endocytic pathway: contents move INTO cell (endocytosis)
During exocytosis, vesicle contents are delivered to ______ ______. The vesicle membrane becomes part of the _____ ______
During endocytosis, the PM forms a _____ _____. The vesicle luminal contents come from ______ _____
What is the function of a vesicle? Give an example
to transport components back and forth in the endomembrane system
ex. from the ER to Golgi
What are the two compartments involved in vesicular transport?
1. donor compartment
2. target compartment
mRNA arrives in the _____ and translation start on the _____ in the cytosol
What is a cytosolic protein?
it is translated in the cytosol; no sorting signal (has a default location)
Mitochondria and chloroplasts have their own _____ and ____ BUT most proteins are ____-____
Where are proteins translated in mitochondria and chloroplasts? and what are they targeted by?
translated in the cytosol
targeted by a signal sequence
How do proteins remain in the cytosol?
-remain unfolded in the cytosol by association with hsp70 chaperones
What happens to protein while translation is still occurring?
-insertion of protein into the ER starts (co-translational translocation)
Describe the cleavage of signal peptide?
-signal sequence on growing polypeptide chain
-signal peptidase binds to translocator which is attached to the ribosomal subunits
-signal peptide is cleaved and released from the translocator
-mature polypeptide chain stays in the ER lumen
What do pancreatic cells make a lot of?
-make a lot of secreted proteins
What is the pulse-chase experiment?
-a technique in which the cells are provided with a short "pulse" of radioactive AA
-then there is a chase after the AA as they are incorporated into proteins
Proteins move from ____ --> _____--> _____.
What is the chase time for each?
RER (3 mins) --> Golgi apparatus (20 mins) --> secretory vesicles (120 mins)
What are the two secretory pathways?
1. constitutive pathway: continual production of secreted proteins (e.g. collagen)
2. regulated pathway: proteins are stored in secretory granules ready for export in response to a stimulus (e.g. neurotransmitter)
What are the 3 types of protein sorting mechanisms?
1. Gated: proteins move between the cytosol and nucleus through nuclear pore complexes (NPCs)
2. Transmembrane: protein translocators needed to transport specific proteins across a membrane
3. Vesicular: membrane-enclosed transport vesicles ferry proteins from one compartment to another
What is a signal sequence?
-a stretch of the AA sequence of a protein that directs the protein to the correct location in the cell
What do specific signal sequences direct proteins to? (different components in a cell)
nucleus, mitochondria, ER, peroxisomes, etc.
What are signal sequences recognized by?
sorting receptors that take proteins to their destination
Where are signal sequences often found on a protein? Where does it direct the protein to?
N-terminus end (amino-terminal end)
______ ______ can remove the signal sequence from the protein
Signal sequences can also be _____ _____ of AA which remain part of the protein.
Where does translation start?
Is the signal sequence hydrophilic or hydrophobic?
Protein is inserted through a membrane by a ____ _____
The signal sequence is ______, left behind in the _____ membrane, secreted protein ends up in the ER _____.
Secreted protein moves in transport vesicles via the ______ ______
Secreted protein is released by ________ at the PM
What determines the orientation of a protein?
NH2 signal sequence