Chapter 15 - Protein Sorting to Intracellular Compartments pt. 1 Flashcards
Organelle duplication and growth requires a supply of what?
1) New lipids to make more membranes
2) New proteins, both membrane proteins and soluble proteins, that will occupy the interior of the organelle
Proteins for organelle duplication and growth must be ___ and accurately ___ to their destined organelles.
sorted, delivered
What instructs the correct delivery of proteins to their targeted organelles?
Amino acid sequence.
Similar to how a letter has a mailing address.
What are the two types of protein synthesis?
1) Synthesis from free polyribosomes
2) Synthesis from membrane-bound polyribosomes
What type of proteins does synthesis from free polyribosomes create?
Proteins floating freely in the cytosol.
What type of proteins does synthesis from free polyribosomes NOT create?
Transmembrane proteins nor proteins that are going to be exoctyosed from the cell.
(T/F) Synthesis from membrane-bound polyribosomes evolved along with internal membrane structures.
True
Synthesis from membrane-bound polyribosomes creates what types of proteins?
Membrane associated proteins and proteins in endomembrane vesicles.
Synthesis from membrane-bound polyribosomes are present only what kind of cells?
Eukaryotic
A polyribosome is a messenger RNA that has multiple ribosomes on its progressing from its ___ to ___ end.
5’, 3”
For both cases of protein synthesis, a polyribosome starts of as a what?
As a monoribosome (i.e., one ribosome).
Which end of the messenger RNA does polyribosomes start?
The 5’ end in the cytosol.
Where do sorting signals direct proteins?
To their target organelles
The synthesis of virtually all proteins begins where? What are some exceptions?
On ribosomes inside the cytosol. Some exceptions are mitochondria and chloroplast proteins.
What happens to proteins that lack sorting signals?
These proteins will remain in the cytosol.
Where are some examples sorting signals will direct proteins?
The nucleus, mitochondria, chloroplast, and the ER.
How can an organelle transport a protein across its membrane(s) which are normally impermeable to large and hydrophilic molecules?
Proteins from the cytosol move into:
1) Nucleus via nuclear pores
2) ER, mitochondria, or chloroplasts
3) Proteins move onward from ER
For nucleus proteins what types of gates and transport do proteins rely on?
Selective gates which actively transport the proteins.
How do proteins transverse across the membrane of the ER, mitochondria, or chloroplasts?
By protein translocation in the membrane. Protein must be unfolded and “snake” across the membrane.
Proteins that move onward from one compartment of the endomembrane system to another are transported by what?
Transport vesicles
How do proteins move onward from one compartment to the next?
They pinch off from one compartment and then fuse with the membrane of a second compartment.
What do proteins usually deliver when being transported to another compartment?
Soluble cargo proteins and membrane proteins.
How does the nuclear envelope get lipids and membrane proteins?
By backfilling along the appropriate lipid layer because the lipids themselves are not covalently linked and the membranes are contiguous.
How are proteins transported through the nucleus?
Via nuclear pores
The protein meshwork in the center of the nuclear envelope: each protein has a ___.
short repeated sequence; FGs.
The protein meshwork in the center of the nuclear envelope and nuclear pores of repeated sequences that ___ to each other.
Bind
The protein meshwork in the center of the nuclear envelope and nuclear pores form a mesh to prevent what?
Large molecules passing through.
What are protruding both sides of the pore complex inside the nuclear envelope and nuclear pores?
Protein fibrils
Protein fibrils ___ to form a basket-like structure on the nuclear side of nuclear pores.
converge
Proteins destined to the nucleus must display what sorting signal?
Nuclear Localization Signal (NLS)
What is the Nuclear Localization Signal (NLS)
It serves as both a mailing addresses and a ticket for protein transport.
What signal is used when NSL is recognized by proteins?
Nuclear Import Receptor (NIR)
Which signal directs the protein complex to a nuclear pore by grabbing the tentacle-like cytosolic fibrils?
Nuclear Import Receptor (NIR).
Once in the pore, NIR grabs onto the ___ of the meshwork proteins, opening a ___ through the pore.
FG repeats, passage
NIR bumps along the nuclear pore from one FG to another until what?
Enters the nucleus
NIR and the cargo protein dissociates from each other thereby what?
Completing the delivery.
Which cycle of active transport transports protein into, and out of, the nucleus?
Ran-GTP cycle
In the nucleus, ___ protein encounters a ___ called Ran, which carries a GTP.
NIR-cargo, GTPase
Ran binds to ___, causing the release of cargo protein.
NIR
Which complex is transported back to the cytosol after the release of a cargo protein?
NIR-Ran-GTP
Ran hydrolyzes what in the cytosol with the help of Ran GAP?
GTP
What does GTP stand for?
GTPase Activating Protein
NIR dissociates with ___, and ready to transport another nuclear protein.
Ran-GDP
What type of conformation do proteins remain while being transported via nuclear pores?
Fully folded
At what speed do proteins travel through nuclear pores?
Very high speeds - about 1000 translocations per second.
Import and export of proteins via nuclear pores share what?
Similar mechanisms
Which organelle(s) have their own genome, which can make some of their own proteins?
Mitochondria and Chloroplast
Though they make some of their own proteins, most of Mitochondria and Chloroplasts’s ___ are encoded by the nuclear genome and imported from the cytosol.
Protein
How many membranes do mitochondria and chloroplasts have?
Two
Do proteins pass through both membranes of mitochondria and chloroplasts?
Yes
How do mitochondria and chloroplasts get proteins from the cytosol?
From proteins already synthesized on free polyribosomes. Hence, post-translational transport.
How do mitochondria and chloroplast obtain lipids?
By lipid transporters
By lipid transporters, mitochondria and chloroplasts extract ___ from the ER and deliver them to these organelles.
Phospholipids
For protein transport into mitochondria and chloroplasts, the protein precursor protein is ___ and its ___ is recognized and bound by a specific ___ on the outer membrane, which is associated with a pore-forming ___ protein.
unfolded, signal sequence, receptor protein, translocator.
For protein transport into mitochondria and chloroplasts, which precursor complex diffuses laterally until it meets a second translocator on the inner membrane?
protein-receptor-translocator complex
For protein transport into mitochondria and chloroplasts, the two translocators transport the protein across both the ___ and ___ membrane.
outer, inner
(T/F) For protein transport into mitochondria and chloroplasts, after translocator transport the protein across both the outer and inner membrane, the signal peptide is then cleaved off.
True
For protein transport into mitochondria and chloroplasts, how do chaperones assist protein transport?
1) Keeping protein unfolded in the cytosol.
2) Pulling proteins across the membrane.
3) Promoting correct protein folding in the matrix
For protein transport into chloroplasts, which proteins share the same transport mechanisms as mitochondria matrix protein?
Stroma proteins.
For protein transport into chloroplasts, for proteins destined to the thylakoid lumen, what are the two signal peptides?
1) One for chloroplast stroma, which will be cleaved off in stroma.
2) This will expose the second signal peptide for thylakoid lumen.
For protein transport into chloroplasts, the exposed thylakoid signal peptide will target the ___ to the ___ via a similar mechanisms as the one for stroma proteins.
protein, lumen
How do you identify an unknown protein and study the function of this protein after identification?
Looking for a storing signal amino acid sequence.
