What is the default pathway for proteins without an end label?
Transmembrane transport is performed by what "special machine?"
protein translocator, which is composed of transmembrane proteins and opens up an aqueous pore in the hydrophobic bilayer
What is the space between the outer membrane and inner membrane?
What is bordering the inner membrane in the center of the mitochondrion?
Most mitochondrial proteins are made in the cytosol, though some are made in mito itself. when protein translocates newly synthesized protein, it is called
proteins shopped to mitochondria use what kind of import?
What are the step to transmembrane transport into mitochondria?
1. precursor proteins contain signal sequences
2. the mitochondrial protein does not fold immediately, but it chaperoned by chaperones to the mito.
c. TIM& TOM are the protein translocators
To get through the membranes of mitochondria, proteins have signal sequences that bind where?
receptor protein in TOM complex
When is ATP used in transporting protein though the mitochondrial membrane?
ATP for push through TOM/TIM and in the matrix (pull), also energy inherent in the membrane potential
what components of the cell use transmembrane transport from the cytosol?
Can proteins be moved across rough ER bilary boundary while translation is still going?
Yes, this is called co-translational import.
What are the steps of co-translational import of proteins into the rough ER?
1. SRP, floating free in cytosol, recognizes and binds ER transport signal sequences
2. translation halts until
3. SRP finds a SRP receptor in ER membrane
The SRP, signal recognition particle, is a key player in what transport?
what are the steps of SRP binding?
1. SRP floats free in cytosol, recognizes and binds ER import signal sequences
2. SRP finds SRP receptor in ER membrane
3. STP finding SRP receptor unbinds it to the signal sequence, and the signal sequence binds to the protein translocator, which thread the protein through as it is translated
What end of the signal sequence binds to TOM and the ER protein translocator?
NH2, and then rest of new protein threaded through as it is made while NH2 stays stationary inside protein translocator
What role does signal peptidase play?
It cleaves off the NH2 of the signal sequence after translation into the ER membrane through protein translocator
peptides with stop and start sequences
ER lumen protein is misfolded. what happens?
chaperone assists it through translocator out of cell, tagged by ubiquitin and proteosome degradation
What makes disulfide bonds in newly translocated protein?
Protein disulfide isomerases,
What assists the newly translocated protein in folding?
When does folding/ disulfide bond formation happen for translocated proteins?
as it is being translated
glycosylation adds what to what?
sugar residues to the lumindal domain of transmembrane proteins
What are the misshapen proteins identified by?
chaperones in ER lumen
proteosome is ATP dependent. true or flase
how does ubiquitin bind?
misfolded proteins expose a signal sequence (AA sequence) that normally wouldn't be exposed and ubiquitin is enzymatically added
Where are lipids made?
smooth ER= enzymes catalyzing phospholipid synthesis reside on the cytosolic face of ER bilayer
How do fatty acids GET to the enzymes on the cytosolic ER?
fatty acid binding proteins
are flippases random? what about scramblases?
flippases are selective.
scramblases deliver newly synthesized phospholipids to luminal half...RANDOM
Do scramblases and flippases use ATP
yes, they use ATP
how are phospholipid exchange proteins useful in terms of lipid transport?
They extract lipids from cytosolic face of ER to ship to mitochondria and peroxisomes.
They extract, sequester in hydrophobic pocket, then is carried to mitochondria or peroxisomes
Clathrin has what kinds of chains that create what?
heavy and light that form a triskelion
How is clathrin budding started?
1. cargo receptors, which bind cargo on luminal side and adaptors on cytosolic, bind cargo.
2. cargo receptors bind adaptors.
3. this begins bud formation
4. clathrin is bound to adaptors
5. dynamin, protein purse string that drives scission, separates the bud from donor membrane
What do GTPases do in general?
exhange GDP for GTP
COPI and COPII coats are assembled under control of
What role does Sar1 play?
It is really called Sar1-GEF. It is in the donor membrane. Sar-1-GDP attaches to Sar-1-GEF and GTP is attached to Sar-1-GDP (now GTP). Sar-1GTP is conformationally changes, a hydrophobic domain exposed, and previous cytosolic protein inserted into donor membrane bilayer.
Sar1-membrane bound (Sar-1-GTP) does what
is a scaffold for COPII coat proteins, sec adaptors link cargo proteins
How does a transport vesicle make contact with the target membrane>
1. first, the coat must be shed.
2. second, the target membrane "fishes" for the donor vesicle by using a rab effector, or tether.
3. The tether hooks a rab-GTP on the donor membrane. SNARES also contribute specificity
How do donor membranes target with target membranes?
SNAREs are required.
1. v-SNARE on donor vesicle membrane
2. t-SNAREs on targt membrane
What kind of interaction between v snares on donor vesicle and t snares on target vesicle mediate docking?
How does fusion occur?
t-v snares are intertwined and bend towards their respective membranes, forcing the energetically unfavorable merger to occur
NSF does what in fusion?
separates the four SNAREs present in post-fusion complex, using energy from ATP and prepares SNAREs for another round
HIV co-opts SNARE method, how?
virus provides v-and t-snare equivalents. Target membrane does not co-operate. But the target cell does expose CD4/chemokine receptor and the virus binds to that. Virus inserts one snare into membrane, uses the other in typical SNARE formation/fusion.
What is the Golgi's function
to add carbs to proteins and decide twhere to send them
Only proteins that are fully assembled and folded can leave where?
What binds antibodies when they aren't fully assembled to prevent it from leaving the ER?
How can the restriction against misfolded proteins leaving the ER be bad?
In cystic fibrosis, a transmbembrane protein Cl- channel is misfolded, but it is still functional. however, it can't leave the ER to get to the plasma membrane.
How do proteins that function in the ER lumen itself get back t the lumen?
Chaperones, an example of this, return by receptor-mediated budding and fusion
what differentiates cis face and trans face of Golgi?
Cis face= entry point of vesicles from ER.
Trans face=exit point for vesicles destined for plasma membrane. sorting occurs here as well.
What are the steps of autophagy?
1. donor organelle donates membrane
2. membrane closes around organelles
3. lysosome fuses and digests
what is the function of autophagy?
to remove damaged organelles and provide nutrients in periods of starvation
Where do hydrolases for lysosomes come from?
from trans side of golgi
What is the pathway for an acid hydrolase to get to a lysosyme?
1. the address code is a sugar phosphorylated.
2. the sugar, M6P, take place in cis and mid golgi.
3. trans Golgi, M6P bind to M6P receptor, and a shuttle vesicle is budded using clathrin.
4. fuses with an early endosome. low luminal pH releases M6P hydrolases from the receptor.
5. becomes a lysosome
What is I cell disease?
genetic defect in golgi enzyme that phosphorylates mannose at 6 position .
"inclusion" cell disease, since lysosomes are swollen due to not being able to digest due to lack of acid hydrolases
the constitutive exocytotic pathway is called this why?
Not signal-mediated, but default. any protein sequence that doesn't have M6P or other signal sequence goes to the plasma membrane this way from the golgi.
it operates continously, hence, "constitutive"
what kind of cells use constitutive exocytotic pathway?
all, since all need to maintain plasma membrane
some proteins are also secreted by constitutive exocytotic pathway. t or f
how does the regulated exocytotic pathway work?
- it's triggered and requires a signal to the professional cells, e.g. hormones, neurotransmitters, digestive enzymes
- the vesicles hang out in cytosol and mature.
-they either fuse together, condense protein cargo, and/or undergo proteolytic processing to convert contents to active form
-dense vesicles dock at membrane but do not release contents until signal is performed (synapse, Ca2+)
what is pinocytosis?
"cell drinking", which is non-specific and constitutive. capture extracellular fluid via plasma-derived vesicles, in order to promote plasma membrane turnover (they fuse with lysosomes) and internalization of nutrients that lack receptor.
What kind of particles are up for phagocytosis?
large, insoluble particles like bacteria, dead cells, and debris. Only those who can trigger the phagocytic response based on surface chemistry and interaction with receptors on phagocyte. specific.
mechanism of phagocytosis
- sequential engagement of ligands on particle surface and receptors on phagocyte plasma membrane
-myosin/actin is triggered by receptor binding to ligand and membrane/cytoplasm is extended around victim
-phagosome fuses with lysosome
1. receptor bind LDL, which binds adaptors which bind clathrin inside cytosol
2. fusion ends when fuses with early endosome, which matures into lysosome, digestion of cargo and some receptors (like LDL) are recycled, some are degraded
opportunistic endocytotic ligands: what does this mean?
for bacteria/toxins/virsuses to gain entry to cells by mimicking other stuff
what are three ways that bacteria/etc can get out/activate of the endosome once endocytosed?
1. use a protein translocator, like in botox toxin. The low pH triggers the heavy chain to act as protein translocator, and translocates light chain into cytosol as toxin, which is a selective protease that targets SNAREs at neuromuscular junction
2. fuse with endosome membrane: induce exocytosis from endosome with pH as a trigger. many membrane encapsulated viruses do this, like HIV
Legionella is impervious to hydrolytic enzymes of lysosome.
TOM and TIM interact how?
they align when protein from translocation is being translocated into cytosol.
co-translational transport is used for what organelle?
What are multipass proteins?
proteins that have multiple stop-start sequences for transmembrane domains, etc, into ER membrane
Clathrin is a protein coat. where is it used for transport?
to and from trans golgi/endosomes/plasma membrane. also for secretory vesicles
Clathrin is normally _________ in location
COP I/COPII go from ER to and from golgi. how does it work?
Sar-1-GDP, after binding to Sar1GEF (GTPase), gets transformed into Sar-1-GTP and undergoes conformational change via hydrophobic interior spot that was exposed. the domain exposed embeds in membrane and is scaffold for adaptors and other proteins. forms two later coat and deforms membrane to produce a bud
CFTR is what
a chloride channel in ER
what's the difference between exocytotic vesicles and secretory vesicles?
exocytotic comes from the golgi and is constinuous
-secretory vesicles also come from golgi but are regulated from signals
Transport to mitochondria and peroxisome is different how?
there are no transport vesicles, so new lipids from smooth ER taken by phospholipid proteins in hydrophobic pocket
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