Question 1
Question
Post-translational translocation of non-secretory proteins across membranes could occur in which organelles?
Answer
-
mitochondria
-
chloroplasts
-
nuclei
-
Golgi
-
ER
-
peroxisomes
-
lysosomes
Question 2
Question
Select the correct sequential steps for cotranslational translocation (signal hypothesis):
Answer
-
ER signal sequence is translated at free ribosome
-
Sequence allows ribosome to bind to a translocator on RER
-
Pore is formed and polypeptide is translated through to the RER lumen
-
Signal peptidase cleaves signal sequence
-
Protein is released into the ER lumen
Question 3
Question
The discovery of cotranslational translocation involved:
Answer
-
Secretory proteins translated in vitro were smaller than those in vivo. Microsomes from ER added to in vitro proteins resulted in larger size.
-
Secretory proteins were the same size in vitro and in vivo.
-
Secretory proteins translated in vitro were larger than those in vivo. Microsomes from ER added to in vitro proteins resulted in correct size.
Question 4
Question
Signal sequences:
Answer
-
vary greatly but have 6+ hydrophobic aa string at N terminus
-
vary greatly but have 8+ hydrophobic aa string at N terminus
-
vary greatly but have 6+ hydrophobic aa string at C terminus
-
vary greatly but have 8+ hydrophobic aa string at C terminus
Question 5
Question
Signal recognition particle can bind to signal sequences of multiple shapes and sizes because:
Answer
-
Hydrophilic pocket lined with methionine, which has inflexible side chains.
-
Hydrophobic pocket lined with methionine, which has flexible side chains.
-
Hydrophobic pocket lined with methionine, which has inflexible side chains.
Question 6
Question
Select the steps for SRP function:
Answer
-
SRP binds to small ribosomal subunit
-
SRP binds to large ribosomal subunit.
-
Binding pocket fits around nascent chain exit site and binds to ER signal sequence.
-
Translational pause domain positions at interface between ribosomal subunits.
-
SRP binds to SRP-R.
-
Mechanism possibly related to GDP binding sites near SRP-R.
-
SRP released, translation continues embedded in ER.
-
ER signal sequence binds to hydrophobic site on inside of locator, opening the channel.
-
Polypeptide extruded into ER, peptidase cleaves signal.
Question 7
Question
ER signal sequence is checked:
Question 8
Question
Translocator for secreted proteins in ER is called:
Answer
-
Sec 59.
-
Sec 51.
-
Sec 61.
-
Sec 63.
Question 9
Question
Sec 61 has opening in side for:
Answer
-
Integration of TMDs.
-
Cleaved signal sequence to diffuse into membrane.
-
Ribosome to insert peptide from side.
-
Hydrophobic influence in Sec 61 pore.
Question 10
Question
A type I TMD has:
Answer
-
N terminus in ER lumen.
-
C terminus in ER lumen.
Question 11
Question
A type II TMD has:
Answer
-
N terminus in ER lumen.
-
C terminus in ER lumen.
Question 12
Question
For 1 pass TMDs, orientation is determined by:
Answer
-
Location of (+) charge, always goes to cytosol
-
Location of (+) charge, always goes to ER lumen
-
Location of 3 aa repeat, always goes to cytosol
-
Location of 3 aa repeat, always goes to ER lumen
Question 13
Question
In two TMD insertion, the signal is cleaved.
Question 14
Question
In multiple TMD insertion:
Answer
-
There is an internal start-transfer sequence and C-terminus stop-transfer sequence.
-
There is an N-terminus start-transfer sequence and a C-terminus stop-transfer sequence.
-
There is an internal start-transfer sequence and internal stop-transfer sequence.
-
There is an N-terminus start-transfer sequence and an internal stop-transfer sequence.
Question 15
Question
Many ER resident proteins stay in the ER because:
Answer
-
They have an ER retention signal.
-
They are too small to be absorbed into vesicles.
-
They are anchored on a special receptor called ER-R.
Question 16
Answer
-
Protein disulfide isomerase.
-
Protein disulfur isomerase.
-
Protein disulfide isomerate.
-
Protein disulfur isomerate.
Question 17
Question
PDI's function is:
Answer
-
Formation of disulfide bonds between sulfhydryls of cysteins.
-
Formation of disulfide bonds between sulfhydryls of nucleotides.
-
Binding to unfolded proteins to prevent aggregation.
-
Binding to unfolded proteins to facilitate aggregation.
Question 18
Answer
-
Binding Protein.
-
Binder Protein.
-
Binding in Protein.
Question 19
Question
BiP functions by:
Answer
-
Binding to unfolded proteins and preventing aggregation.
-
Binding to unfolded proteins and promoting aggregation.
-
Forming disulfide bonds between sulfhydryls of cysteins.
-
Forming disulfide bonds between sulfhydryls of nucleotides.
Question 20
Question
BiP and PDI aid in:
Answer
-
Secretory pathway in the Golgi.
-
Secretory pathway in the ER.
-
Proper folding of proteins.
-
Aggregation of proteins.
Question 21
Question
Glycosylation aids in:
Question 22
Question
Which is more common at 90%?
Answer
-
N-linked glycosylation.
-
O-linked glycosylation.
Question 23
Question
N-linked glycosylation occurs by attaching sugar residues to:
Answer
-
Amide nitrogen of asparagine.
-
Amide nitrogen of cysteine.
-
Amide nitrogen of serine.
Question 24
Question 25
Question
OST transfers what structure to the target side chain during N-linked glycosylation?
Answer
-
14 sugar compound of GlcNAc, mannose, glucose.
-
14 sugar compound of GlcNAc, mannose.
-
16 sugar compound of GlcNAc, mannose, glucose.
-
16 sugar compound of GlcNAc, mannose.
Question 26
Question
OST glycosylates:
Question 27
Question
Initial sugars that form the basis of all N-linked glycosylations are:
Answer
-
2 GlcNAc, 3 Man
-
3 GlcNAc, 2 Man
-
2 Glu, 3 GlcNAc
-
3 Glu, 2 GlcNAc
-
2 Man, 3 Glu
-
3 Man, 2 Glu
Question 28
Question
OST aids in glycosylation of cytosolic proteins.
Question 29
Answer
-
Holds sugar structure awaiting transfer by OST.
-
Builds sugar structure awaiting transfer by OST.
-
Facilitates ATP hydrolysis of OST.
-
Holds energy for sugar transfer in pyrophosphate bond.
-
Uses ATP to transfer sugar.
-
Uses GTP to transfer sugar.
Question 30
Answer
-
Is associated with every Sec 61 translocator and each has a dolichol anchor nearby.
-
Is associated with some Sec 61 translocators and each has a dolichol anchor nearby.
-
Is associated with all Sec 61 translocators but not dolichols.
Question 31
Question
OST catalyzes the addition of sugar groups:
Answer
-
During translation of the target protein.
-
After the signal peptide is cleaved.
-
The instant translation finishes.
Question 32
Question
Which sugar combination is associated with entrance into the Golgi?
Answer
-
8 Man, 2 GlcNAc
-
6 Man, 2 GlcNAc
-
2 Man, 8 GlcNAc
-
2 Man, 6 GlcNAc
Question 33
Question
O-linked glycosylation:
Answer
-
Makes up about 90% of glycosylation events.
-
Makes up about 10% of glycosylation events.
-
Involves attachment of sugar to hydroxyl group of serine.
-
Involves attachment of sugar to hydroxyl group of threonine.
Question 34
Question
Synthesis of precursor oligosaccharide begins:
Answer
-
In membrane layer.
-
Cytosolic face.
-
ER lumen face.
Question 35
Answer
-
Is very hydrophobic, spans bilayer 3+ times.
-
Is very hydrophilic, spans bilayer 3+ times.
-
Is very hydrophobic, spans bilayer 2 times.
-
Is very hydrophilic, spans bilayer 2 times.
Question 36
Question
Synthesis on dolichol:
Answer
-
Is en bloc.
-
Is one sugar at a time.
Question 37
Question
Dolichol's pyrophosphate bond is located:
Question 38
Question
During flip of dolichol, (Glc)3(Man)9(GlcNAc)2 turns into (GlcNAc)2(Man)5.
Question 39
Question
ER chaperones require:
Question 40
Question
Calnexin & calreticulin:
Answer
-
Prevent unproperly folded proteins from leaving the ER.
-
Keep ER resident proteins critical for proper folding inside the ER.
-
Are the only proteins needed for proper management of proteins in the ER.
Question 41
Question
Calnexin is membrane bound.
Question 42
Question
Calreticulin is membrane bound.
Question 43
Question
Select the proper steps for calnexin function:
Answer
-
Calnexin recognizes a single glucose after glucose trimming.
-
Calnexin recognizes a double glucose after glucose trimming.
-
ER resident glucosidase removes final glucose(s) off of protein.
-
Calreticulin recognizes absence of glucose and binds.
-
If proper folding occurs, protein is bound by glucosyl transferase.
-
Inproperly folded proteins have sugars added back onto their N-linked oligo to go back through cycle.
Question 44
Question
If proper folding fails:
Answer
-
Protein goes through retrotranslocation.
-
Protein possibly goes back through Sec61.
-
N-glycanase removes oligosaccharide chains en bloc in ER.
-
Oligosaccharide chains removed in cytosol.
-
Ubiquitin marks proteins for degradation by recognizing certain sequences that should not be exposed in properly-folded proteins.
-
Lysosome breaks down ubiquitin-marked proteins.
-
Proteaomse processes ubiquitin-marked proteins.
Question 45
Question
Consider proteins that take too long to fold:
Answer
-
They are processed in the same manner as proteins that are incorrectly folded once recognized.
-
They have an organic timer mediated by mannosidase.
-
Calnexin cycle resets the mannose timer.
-
Proteins that fold properly keep all their mannoses.
Question 46
Question
Unfolded protein response involves:
Answer
-
Accumulation of unfolded proteins in ER.
-
Activation by high proteasome activity.
-
Increased transcription of genes involving ER chaperones, retrotranslocation proteins, protein-folding proteins.
-
Involve IRE1.
Question 47
Answer
-
is a transmembrane protein kinase.
-
is an ER chaperone catalyst.
-
autophosphorylates.
-
dimerizes.
-
trimerizes.
-
has endoribonuclease domain that edits a specific mRNA in cytosol.
-
affects activation of genes in nucleus through mRNA editing.
-
enters the nucleus after signaling to affect gene transcription.
Question 48
Question
____ controls coat assembly.
Answer
-
GTP binding protein.
-
Sar1.
-
Sec61.
-
ATP binding protein.
-
ATPase.
Question 49
Question 50
Question
Sar1 is associated with COPI vesicles.
Question 51
Answer
-
is an ER membrane protein.
-
is a cytosolic protein.
-
is a type of GEF.
-
binds Sar1-GDP and catalyzes release of GDP and binding of GTP.
-
binds Sar1-GTP and catalyzes hydrolysation and subsequent release of GDP.
-
is involved with COPI vesicles.
-
is involved with COPII vesicles.
Question 52
Question
Select the correct steps for COPII coat assembly:
Answer
-
Sar1-GTP serves as a binding site for Sec23 & 24.
-
Sec23 & 24 select cargo.
-
Sec13 & 31 proteins form second layer to COPII structure.
-
Sec16 increases coat polymerization efficacy.
-
Sec17 increases coat polymerization efficacy.
-
Sec23 promotes GTP hydrolysis of Sar1-ATP.
-
Sec23 promotes GTP hydrolysis of Sar1-GTP.
-
Sar1-GDP is released from vesicle membrane, allowing coat to rapidly dissemble.
-
t-SNARE is exposed on surface, allowing fusing process to begin.
-
v-SNARE is exposed on surface, allowing fusing process to begin.
Question 53
Question
Rab-GDP is active in the cytosol.
Question 54
Question
Rab-GTP is free in the cytosol.
Question 55
Question
Select the correct steps for vesicle fusion:
Answer
-
Vesicle binding is mediated by Rab GTPase.
-
Cytosolic Rab-GDP converted to Rab-GTP by GEF.
-
Rab-GTP binds to Rab effector on target membrane.
-
t-SNARE and v-SNARE become close enough to interact and "hook."
-
NSF with an alpha-SNAP binds the SNAREs.
-
NSF catalyzes hydrolysis of ATP, forming energy needed to dissociate SNARE complexes.
-
Rab protein hydrolyzes its bound GTP releasing Rab effector.
-
Rab-GDP is released into cytosol for next cycle.
Question 56
Question
Studies with VSVG-GFP revealed:
Answer
-
Some vesicles detached from the ER directly fused with the Golgi if the travel distance was short.
-
COPII vesicles traveled toward the Golgi when originally thought COPII did retrograde transport back to the ER.
-
If Golgi was several micrometers away, vesicles en route to Golgi fused prior to Golgi contact, forming cis-Golgi network.
-
Retrograde vesicles budded off the Golgi toward the ER.
-
trans-Golgi network formed after trans-Golgi pushed out of Golgi from cisternal maturation.
Question 57
Question
Purpose of retrograde transport to ER:
Question 58
Question
Retrograde transport to ER from Golgi involves COPI while retrograde transport from Golgi to Golgi involves COPII.
Question 59
Question
COPI coat proteins are composed of:
Answer
-
6 large cytosolic polypeptide complexes (coatomers).
-
4 large cytosolic polypeptide complexes (coatomers).
-
Coatomers with alpha and beta subunits.
-
Whole coatomers, no subunits.
Question 60
Question
COPI vesicles are controlled by:
Question 61
Question
Select the proper steps for COPI formation:
Answer
-
ARF-GDP is weakly tethered to the Golgi membrane by a weak covalent protein mod on N-terminus.
-
ARF-GTP is strongly tethered to the Golgi membrane by a strong covalent protein mod on N-terminus.
-
GEF on Golgi catalyzes formation of ARF-GTP. ARF now strongly tethered to Golgi membrane.
-
Tight association of ARF-GTP serves as foundation for coatomer formation on COPI vesicles.
-
Coat dissembles and Rab mediates binding to target membrane.
-
SNARES facilitate fusion to target membrane.
Question 62
Question
Yeast COPI mutants showed protein accumulation in ER. This was because...
Answer
-
Mutant COPI vesicles lacked the ability to perform vesicle transport of proteins to the Golgi apparatus.
-
Mutant COPI vesicles successfully formed vesicles, but the mutation made them immediately fuse back with the ER so transport did not occur.
-
Mutant COPI vesicles could not bring back proteins necessary for anterograde transport to continue.
-
Mutant COPI vesicles fused readily with COPII vesicles, interrupting the transport chain.
Question 63
Question
Because ER resident proteins are so abundant...
Answer
-
They easily get trapped in outgoing vesicles.
-
Retrograde transport is necessary to maintain presence of ER resident proteins in the ER.
-
Specialized receptors prevent ER resident proteins from getting entrapped in outgoing vesicles.
-
ER resident proteins are mostly free in the ER lumen, so outgoing vesicles usually do not trap ER resident proteins, and the cell can replace readily those that do.
Question 64
Question
Soluble ER resident proteins are targeted back to the ER...
Answer
-
By an ER retention signal (KDEL) that passes directly to the membrane, causing a COPI vesicle to form.
-
By an ER retention signal (KDEL) that binds to a special KDEL Receptor in low pHs, allowing retrograde transport.
-
By an ER retention signal (KDEL) that binds to a special KDEL Receptor in high pHs, allowing retrograde transport.
-
By an ER retention signal (KDEL) that binds to KDEL Receptor on COPII vesicles, essentially redirecting the vesicle to the ER before fusion with the Golgi.
Question 65
Question
What special signal targets KDEL receptor back to the ER?
Answer
-
KKXX signal on C terminus.
-
KKXX signal on N terminus.
-
KDEL signal on C terminus.
-
KDEL signal on N terminus.
-
3 Man, 2 Glu on C terminus.
-
3 Man, 2 Glu on N terminus.
Question 66
Question
KDEL Receptor binds to KDEL to:
Question 67
Question 68
Question
KDEL is released from KDEL-R at:
Question 69
Question
ER has a ____ pH compared to the Golgi.
Question 70
Answer
-
outer phospholipids of COPI vesicles.
-
alpha and beta subunits of COPI vesicles.
-
special KDEL-R receptor on COPI vesicles.
-
KDEL-R.
Question 71
Question
It's been observed that yeast mutants that lack COPI alpha and beta subunits:
Answer
-
still have successful retrograde transport of KDEL-signal proteins.
-
have proteins that need to be transported back to the ER remaining in the Golgi.
-
send KDEL-marked proteins to lysosomes.
-
lack the problem of having ER-resident proteins being erroneously sent to the Golgi.
Question 72
Question
Forward movement of proteins through the Golgi involves vesicles.
Question 73
Question
Backward movement of Golgi enzymes involves vesicles.
Question 74
Question
In cisternal maturation, trans becomes medial and medial becomes cis.
Question 75
Question
Scale-covered algae:
Answer
-
had cell-wall glycoproteins assembled in the Golgi that were 20X larger than any observed vesicle.
-
had cell-wall glycoproteins that were small enough to fit inside vesicles.
-
had cell-wall glycoproteins that were about as large as vesicles, spurring additional research into cisternal maturation.
Question 76
Question
Collagen synthesis by fibroblasts:
Answer
-
involves precollagen, a precusor too large for vesicles.
-
involves precollagen aggregates, which have never been seen in vesicles.
-
provides evidence for cisternal maturation.
-
provides evidence for anterograde vesicular transport in the Golgi.
-
provides evidence that retrograde Golgi transport of enzymes occurs.
-
involves trimming of precollagen, the pieces of which are transported backwards via vesicles in the Golgi.
-
involves COPII vesicles to bring enzymes in the Golgi forward as cisternal maturation occurs.
Question 77
Question
Enzymes move retrograde in the Golgi via:
Question 78
Question
The Golgi does what to secreted proteins during processing?
Answer
-
en bloc modifications to the oligosaccharides, where a protein's modification is processed separately and one exchange occurs before exportation.
-
sequential modifications to the oligosaccharides, where each product is another enzyme's substrate.
-
varies different proteins' oligosaccharides.
-
uniforms different proteins' oligosaccharides.
Question 79
Question
A soluble protein sent to the Golgi can only be secreted.
Question 80
Question
Select the correct steps for processing of lysosomal enzymes by the Golgi:
Answer
-
Lysosomal proteins come to the Golgi with (Man)8(GlcNAc)2 oligosaccharide.
-
Lysosomal proteins come to the Golgi with (Man)3(GlcNAc)2 oligosaccharide.
-
2 cis Golgi residents form the M6P.
-
2 medial Golgi residents form the M6P.
-
M6P is an oligosaccharide.
-
N-acetylglucosamine phosphotransferase binds to lysosomal protein signal.
-
N-acetylglucosamine phosphotransferase catalyzes addition of phosphorylated GlcNAc group to carbon 6 of mannose on enzyme oligosaccharide.
-
GlcNAc phosphotransferase can mistakenly add M6P to secretory proteins.
-
Phosphodiesterase removes GlcNAc, leaving a phosphate.
-
Phosphodiesterase removes phosphate, leaving the oligosaccharide.
Question 81
Question
Select the possible destinations of proteins from the t-Golgi network.
Answer
-
PM via constitutive secretion.
-
PM via selective secretion.
-
PM via regulated secretion.
-
Lysosome via late endosome.
-
Lysosome directly.
-
PM directly.
-
ER via retrograde transport.
-
ER directly.
Question 82
Question
Regulated secretion:
Answer
-
involves release of a protein after a stimulus.
-
involves constant and direct secretion of a protein.
-
involves storing a protein in a vesicle for long term storage.
-
involves sending a protein directly to the PM.
-
involves nothing.
Question 83
Question
During protein-storing vesicle formation:
Question 84
Question
Studies show mammalian secretory cells contain:
Answer
-
Chromogranin.
-
Chromogranin A.
-
Chromogranin B.
-
Chromogranin I.
-
Chromogranin II.
Question 85
Question
The Chromogranin proteins in mammalian cells
Answer
-
aggregate only in storage vesicles.
-
aggregate in the t-Golgi network, but only with a pH of 6.5 and 1mM Ca2+.
-
aggregate in the t-Golgi network, but only with a pH of 5.5 and 1mM Ca2+.
-
may be basis for sorting secretory proteins either into regulated or constitutive secretion.
-
is not involved in sorting secretory proteins into regulated or constitutive secretion.
Question 86
Question
Proteins that do not associate with a Chromogranin aggregation:
Answer
-
will not be secreted.
-
will only be secreted from a storage vesicle.
-
will be carried to the PM for constitutive secretion.
-
Chromogranin aggregations do not bind with secretory proteins.
Question 87
Question
Proproteins of constitutive secreted proteins:
Answer
-
undergo proteolytic cleavage to form a mature, active protein.
-
undergo proteolytic cleavage in the t-Golgi network.
-
in mammalian cells are probably processed by furin.
-
in mammalian cells are probably processed by endoprotease PC2.
-
are cleaved once, at C-terminal dibasic sequence.
-
are cleaved once, at N-terminal dibasic sequence.
Question 88
Question 89
Answer
-
is cleaved to form N-terminal B chain and C-terminal A chain connected by disulfide bonds.
-
is a constitutive secreted protein.
-
probably has processing done by carboxypeptidase, which removes 2 basic aa residues.
Question 90
Question
Proteolytic processing is common because
Answer
-
keeps harmful enzymes from acting anywhere except its target organelle.
-
Peptides that are too large need to be contained in proproteins.
-
ex. enkephalins would not be synthesizable without proteolytic processing.
Question 91
Question
SNARE complex is stable because:
Answer
-
long alpha helices that coil to form a four alpha helix bundle.
-
long alpha helices that coil to form a two alpha helix bundle.
-
Hydrophobic residues at central core.
-
Hydrophilic residues at central core.
-
Alignment of aas of opposite charge forming favorable electrostatic interaction.
Question 92
Answer
-
mediates COPI and COPII vesicles.
-
mediates lysosomal enzyme transport vesicles.
-
are diskelions.
-
have three limbs.
-
polymerize to form polygonal lattice.
-
associates with AP complexes when monomer.
-
associates with AP complexes when polymerized.
Question 93
Answer
-
AP1, helps with t-Golgi network to endosome transport.
-
AP1, helps with PM to endosome transport.
-
AP2, helps with PM to endosome transport.
-
AP2, helps with endosome to t-Golgi network transport.
-
AP3, helps with t-Golgi network to lysosome transport.
-
AP3, helps with t-Golgi network to endosome transport.
Question 94
Question
AP1 interacts with:
Answer
-
KDEL.
-
KKXX.
-
YXXo.
-
DXLL.
-
DFGXo.
Question 95
Answer
-
a new type of AP.
-
AP1.
-
AP2.
-
AP3.
-
a clathrin GTPase.
Question 96
Answer
-
can help deliver proteins to melanosomes in skin cells.
-
can help mediate protein transport to specialized compartments.
-
may not need clathrin for its vesicles to function.
-
helps vesicles bypass the late endosome.
Question 97
Question
GGA interacts with:
Answer
-
YXXo.
-
DXLL.
-
DFGXo.
-
Sec61.
Question 98
Question
Clathrin is needed for GGA vesicles.
Question 99
Question
All lysosomal vesicles utilize ARF GTPase to initiate coat assembly.
Question 100
Question
Dynamin is necessary for Clathrin coated vesicles to form.
Question 101
Question
Dynamin polymerizes around the neck of the vesicle bud and hydrolyzes ATP.
Question 102
Question 103
Question 104
Question
ARF hydrolyzes to have conformational change that regulates timing of clathrin depolymerization.
Question 105
Question
Select correct steps for transport of lysosomal enzymes to the lysosome:
Answer
-
M6P receptor binds in TGN.
-
pH must be 5.5 for M6P receptor to function.
-
ARF allows for coat assembly.
-
M6P receptor has YXXF.
-
M6P receptor has YXXo.
-
Dynamin does its thang.
-
Vesicle is uncoated via Hsc70.
-
Rab-GTP binds with Rab effector to facilitate SNARE interactions.
-
M6P receptor dissociates at lysosomal pH, and a phosphatase breaks up M6P.
-
Some M6P is then transferred to cell surface.
Question 106
Question
M6P is present at cell surface:
Answer
-
because it is sent there from the ER.
-
to release lysosomal enzymes into the ECM.
-
to retrieve lysosomal enzymes that were missorted.
Question 107
Question
Microphages can ingest:
Question 108
Answer
-
is actin-mediated.
-
involves pseudopodia that surround target particle.
-
requires substances to transmit signals to inside of the cell.
-
is used by almost all cell types.
Question 109
Answer
-
recognize and bind infection organisms.
-
aid in pseudopodia development.
-
bind to other cells to mark as friendly.
Question 110
Question
Fc receptors allow phagocytic immune cells to target cells marked by Fab.
Question 111
Question
Receptor-mediated endocytosis:
Answer
-
involves clathrin-coated pits.
-
mostly utilizes AP1.
-
mostly utilizes AP2.
-
mostly utilizes AP3.
-
requires GTP hydrolysis to occur.
-
requires that receptors be recycled.
-
involves receptors that are freshly made from the Golgi.
Question 112
Question
The rate-limiting step of ligand internalization is:
Answer
-
number of receptors.
-
GTP concentration.
-
ATP concentration.
-
clathrin abundancy.
Question 113
Question
Ligands for receptor-mediated endocytosis include:
Question 114
Question
Functions of cholesterol include:
Question 115
Question
Water-soluble carriers for lipids called:
Answer
-
lipoproteins.
-
lipocholesterols.
-
lipocarriers.
-
McDonald's.
Question 116
Question 117
Question
LDLs contain more ___ relative to HDLs.
Answer
-
proteins.
-
fats.
-
cholesterol.
Question 118
Question
Shell of LDL/HDLs composed of:
Answer
-
apolipoproteins.
-
polioproteins.
-
cholesterol-containing phospholipid monolayer.
-
cholesterol-containing phospholipid bilayer.
-
cholesterol-containing phospholipid trilayer.
Question 119
Question
LDL/HDL shell is amphipathic because:
Answer
-
outer hydrophilic surface.
-
inner hydrophilic surface.
-
outer hydrophobic surface.
-
inner hydrophobic surface.
Question 120
Answer
-
is the major cholesterol carrier.
-
carries more cholesterol than HDL.
-
has hydrophobic core with about 1500 esterified chol. molecules.
-
has only one apolipoprotein called apoA-100.
Question 121
Answer
-
has one TMD.
-
has two TMDs.
-
has long terminal N exoplasmic segment with ligand binding arm.
-
has long terminal C exoplasmic segment with ligand binding arm.
-
has binding arm with 7 cysteine-rich repeats of 40aa each.
-
has binding arm with 5 cysteine-rich repeats of 30aa each.
-
has YXXP signal.
-
has NPXY signal.
-
binds to AP-1.
-
binds to AP-2.
Question 122
Question
Select proper steps for LDL intake:
Answer
-
Neutral pH of cell surface allows apoB binding to LDL-R binding arm.
-
NPXY signal grabs AP-1 to form clathrin coat.
-
NPXY signal grabs AP-2 to form clathrin coat.
-
Dynamin hydrolyses GTP to pinch off vesicle.
-
Vesicle is shed with Hsc70's help. ARF-GTP to ARF-GDP.
-
Rab interaction allows for SNARE complex formation at pH of 5 at endosome.
-
At acidic endosome, histidine on LDL-R beta-propeller becomes (+).
-
Ligand binding arm now binds to LDL-R beta propeller.
-
LDL is released.
Question 123
Question
In lysosome, LDL:
Question 124
Question
Microvilli are composed of:
Answer
-
actin
-
MTs
-
intermediate filaments
Question 125
Question
Aggregations of small soluble subunits of cytoskeleton fibers are:
Answer
-
polymers.
-
protofilaments.
-
complete structures.
-
monomers.
-
dimers.
-
held together by strong covalent bonds, allowing for strength of the cytoskeleton.
-
held together by weak non-covalent bonds, allowing flexibility.
Question 126
Answer
-
must avoid breaking from mere thermal motion.
-
form lateral connections with adjacent protofilaments.
-
assemble/disassemble only at the ends.
-
can assemble/disassemble in the middle.
-
of intermediate filaments form alpha helix coiled coils.
-
of actin and MTs are formed from globular monomers.
Question 127
Answer
-
are the thinnest structures.
-
measure at 7 nm in width.
-
support the shape of the cell.
-
are made of actin monomers that form 3 chains that twist around each other.
Question 128
Answer
-
has ATP binding site in cleft (facing (-) end) in center.
-
has a distinct polarity +/-.
-
has polarity due to electroactive aa side chains.
Question 129
Question
The plus end of an actin subunit polymer:
Question 130
Question
A lag is seen at the beginning of actin subunit interaction because:
Answer
-
nucleation must occur, which is a slow process.
-
subunits at the plus end are competing for space.
-
ATP hydrolysis takes time to occur.
Question 131
Question
Adding a nucleated actin segment:
Answer
-
worsens lag time.
-
eliminates lag time.
-
doesn't have an effect.
Question 132
Question
Catalysts of nucleation:
Answer
-
allow nucleation to occur quicker.
-
allow structures to build anywhere.
-
target structures to areas needed by the cell.
Question 133
Question
Actin nucleation is often regulated:
Answer
-
by external signals.
-
by genes.
-
by evil scientists.
Question 134
Question
Nucleation catalyzation can occur from:
Answer
-
ARF.
-
KDEL.
-
ARP2/3.
-
Formin.
-
Furin.
Question 135
Answer
-
help catalyze nucleation.
-
capture 2 actin molecules to begin nucleation.
-
dimerize.
-
continue to associate with actin at the plus end.
-
dissociate after nucleation.
Question 136
Answer
-
is structurally similar to actin.
-
has a different plus end compared to actin.
-
allows actin monomers to bind at plus end.
-
remains bound to (-) end of actin polymer.
-
needs an activating factor to free it from accessory proteins that hold its active site out of orientation.
-
is most efficient at a 70 degree angle to preformed actin filament.
-
is associated with leading edge of migrating cells to allow cellular direction change.
Question 137
Question
Actin can hydrolyze its bound ATP:
Question 138
Answer
-
more likely to exist in a filament.
-
more likely to exist as a monomer.
-
more likely to dissociate from the filament.
-
less likely to dissociate from the filament.
Question 139
Question
If the rate of adding subunits to an actin filament is faster than the rate of ATP hydrolysis:
Question 140
Question
But, if the rate of subunit addition is low:
Question 141
Question 142
Question
During treadmilling, the filament is changing length.
Question 143
Answer
-
binds to actin subunits, preventing binding to (+) or (-) end.
-
this is because thymosin blocks the area of the protein that hooks on to the filament.
-
thymosin blocks ATP binding site.
Question 144
Answer
-
decreases rate of elongation.
-
binds to plus side of actin monomer.
-
favors hydrolysation of ATP to ADP.
-
is thought to bind to some formins to "stage" for action on the polymer.
Question 145
Question
Regulation of thymosin and profilin affect overall actin filament formation.
Question 146
Answer
-
binds filaments forcing tight twisting in the structure.
-
helps add monomers to the plus end of the filament.
-
weakens the contacts between subunits.
-
makes actin-ADP dissociation easier.
-
makes actin-ATP association easier.
-
binds preferentially to actin-ADP units.
-
destroys new filaments moreso than old ones.
-
has effects blocked by tropomyosin.
-
increases rate of disassembly.
Question 147
Question
Capping proteins stabilize ends of filaments.
Question 148
Question
Capping proteins are made where actin must be stable for long periods of time, like muscle cells.
Question 149
Question
Microfilaments are necessary for:
Answer
-
cytokinesis.
-
cleavage furrow.
Question 150
Question
Microtubules are the thickest of the cytoskeletal structures at 30nm.
Question 151
Question
MTs are hollow and built from:
Answer
-
11 parallel protofilaments.
-
13 parallel protofilaments.
-
15 parallel protofilaments.
Question 152
Question 153
Question
MTs determine the position of cytoplasmic organelles including vesicles.
Question 154
Question
MTs direct movement of chromosomes during cell division.
Question 155
Answer
-
is a heterodimer.
-
is composed of 3 globular proteins, alpha, beta, gamma subunits.
-
has its globular proteins held together via noncovalent bonds.
-
has alpha and beta subunits.
-
has two nucleotide binding domains for GTP (alpha, beta).
-
GTP is bound at the intersection between the alpha and beta subunits, and can be hydrolyzed.
-
GTP is bound to the beta subunit, and can be hydrolyzed by the beta subunit itself.
-
Alpha subunit is a GTPase.
Question 156
Question
What kind of contacts occur between tubulin subunits?
Question 157
Question
MT alpha subunits are exposed at the minus end.
Question 158
Question
MT beta subunits exposed at minus end.
Question 159
Question
MT elongation involves:
Answer
-
tubulin-GTP binding to the plus end.
-
tubulin-GTP hydrolysis to tubulin-GDP while part of the filament.
-
tubulin-GDP causes curvature to form, weakening MT structure.
-
GTP caps can be formed if polymerization is faster than GTP hydrolyzation.
Question 160
Question
Dynamic instability has:
Question 161
Question
MT are nucleated at centrosomes.
Question 162
Answer
-
has a pair of centrioles.
-
is composed of fibrous centrosome matrix.
-
has about 50 gamma tubulins.
-
divides during interphase to aid with mitosis.
-
has many proteins in the matrix, that catalyze addition of tubulins.
Question 163
Question 164
Question
Gamma tubulin ring complex (gamma TuRC):
Answer
-
is formed from gamma tubulin and other proteins.
-
allows nucleation to occur.
-
binds the plus end of tubulin subunits to its minus end.
-
caps the minus end of the MTs.
Question 165
Answer
-
bind to tubulin subunits to prevent binding to the polymer.
-
facilitate tubulin binding to the polymer.
-
cap the end of the MT to prevent subunit binding.
Question 166
Question
MAPs (MT associated proteins):
Answer
-
prevent binding of subunits to the polymer.
-
bind to the polymer to stabilize.
-
bind to subunits to prevent interaction with the polymer.
Question 167
Answer
-
has motor activity.
-
attaches to the end of the MT to create a stabilizing cap.
-
pries apart the end of a MT.
-
does not interact with the end of the MT.
Question 168
Question 169
Answer
-
are plus end tracking proteins.
-
are plus end tubulin proteins.
-
can attach and stabilize the growing MT to different locations in the call.
-
accumulate and remain attached at the plus end.
Question 170
Question
Intermediate filaments:
Answer
-
are about 10 nm in width.
-
are the thickest filaments.
-
are required for correct cell functioning.
-
can have varied compositions.
-
are constructed only from a particular protein subunit.
-
can be constructed from keratin, vimentin, lamins, etc.
Question 171
Question
IMs can attach to cell junction proteins.
Question 172
Answer
-
strong.
-
weak.
-
brittle.
-
bendable.
-
easy to break.
-
difficult to break.
Question 173
Question
Why are IMs unique?
Question 174
Answer
-
two monomers form coiled-coil dimer.
-
each monomer has globular domain at each N & C terminus.
-
monomers have small, short alpha helical structure.
-
10 protofilaments made up of pentamers form intermediate filament.
-
8 protofilaments made up of tetramers form intermediate filament.
Question 175
Question
Strong lateral connections give IFs rope-like character.
Question 176
Answer
-
outer skin layer made of keratin that functions as a barrier.
-
support and anchor structures to maintain shape.
-
line the outside of the lining of the nuclear envelope.
-
provide strength to long axons of neurons.
Question 177
Question
Different cytoskeletal filaments have different motor proteins.
Question 178
Question
Myosin moves on:
Answer
-
actin, toward (+)
-
actin, toward (-)
-
MT, toward (+)
-
MT, toward (-)
Question 179
Answer
-
is a large family of 37+ motor proteins.
-
typically refers to myosin II.
-
are all (-) end-directed.
-
is a two-headed dimer.
-
has alpha helices that form a coiled-coil tail.
-
has two small chains.
Question 180
Question
Coiled coils of myosin:
Answer
-
have heptad (7) aa repeat sequence.
-
have hydrophobic side chain interactions on 1st and 4th amino acids.
-
have hydrophobic side chain interactions on 2nd and 4th amino acids.
-
hydrophobic side chains weakly bind to form a superhelix.
Question 181
Question
Myosin thick filaments:
Answer
-
are formed by bundles of myosin motor proteins that form a polar contractile unit.
-
have a bare zone in the middle of the filament that has no myosin.
-
has myosin going one way on one side and another way on the opposite side.
-
myosin III is used to make myosin thick filaments.
Question 182
Question
Muscle contraction occurs because:
Answer
-
myosin shortens.
-
myosin and actin slide past each other.
-
myosin and actin shorten.
-
myosin filaments slide past each other.
Question 183
Question
Long thin muscle fibers:
Answer
-
are actually very large single cells.
-
are several cells lined up on a filament.
-
have majority of cytoplasm made up of myofibrils.
-
have most of cytoplasm filled with mitochondria.
-
have contractile units called sarcomeres.
Question 184
Answer
-
are arrays of parallel and overlapping thick (myosin) and thin (actin) filaments.
-
span from Z disc to Z disc.
-
have capZ proteins that cap and stabilize myosin heads.
-
have capZ proteins that cap and stabilize actin heads.
-
span from Z disc to capZ to Z disc to capZ.
Question 185
Answer
-
caps actin on (-) end.
-
caps actin on (+) end.
-
caps myosin on (-) end.
-
caps myosin on (+) end.
Question 186
Question
Straitions seen in sarcomeres are:
Answer
-
dark bands of actin.
-
dark bands of myosin.
-
light bands of actin.
-
light bands of myosin.
Question 187
Question
Thick filaments during contraction:
Question 188
Question
Sarcomere shortens __% of length in __ time.
Answer
-
10%, 1/50th second
-
20%, 1/50th second
-
10% 1/100th second
-
20%, 1/100th second
Question 189
Question
Z disc caps (+) and (-) ends of actin.
Question 190
Question
M line is another descriptor of the "bare zone."
Question 191
Question
M-line contains:
Question 192
Answer
-
binds to actin and spans the length of it. Acts like a molecular ruler.
-
binds to myosin and spans the length of it. Acts like molecular ruler.
-
binds to actin and connects end to Z disc. Acts like molecular spring.
-
binds to myosin and connects end to Z disc. Acts like molecular spring.
Question 193
Question
Which accessory protein binds to myosin and acts like a spring that spans from M line to the Z disk?
Question 194
Question
Troponin is complex of 3 polypeptides essential for beginning muscle ____________ made up of __________.
Answer
-
muscle contraction; Trop I, Trop T, Trop C.
-
muscle contraction; Trop I, Trop T, Trop R.
-
muscle relaxation; Trop I, Trop T, Trop C.
-
muscle relaxation; Trop I, Trop T, Trop R.
Question 195
Question
Tropomysin binds:
Question 196
Question
In absence of Ca2+, Troponin I binds to Troponin T to make I-T complex.
Question 197
Question
Troponin IT complex formation:
Answer
-
pulls tropomyosin out of groove.
-
allows tropomyosin back into the groove.
-
hydrolyzes tropomyosin.
-
phosphorylates tropomyosin.
Question 198
Question
Which troponin binds to tropomyosin:
Question 199
Question
Muscle contraction steps:
Answer
-
SR releases Ca2+ which binds to Troponin C.
-
Tropomyosin moves out of its groove.
-
Myosin head can now bind to actin after ATP binding.
-
Myosin head can now bind to actin after GTP binding.
-
Binding and hydrolysis of ATP/GTP causes conformational change in converter domain.
-
Swinging of lever arm causes head to move along actin.
Question 200
Question
Let's start with contraction just ended:
Answer
-
Myosin is attached to actin microfilament without a nucleotide.
-
Head is at 45 degree angle to filament.
-
Head is at 60 degree angle to filament.
-
ATP quickly binds and causes a conformational change in lever arm.
-
Myosin dissociates from actin.
-
As Ca2+ is taken up into SR by calcium P pump, Troponin I & T form IT complex.
-
ATPase myosin activity cleaves ATP to ADP and Pi.
-
Conformational change causes lever arm to swing 90 relative to filament, binds to actin.
-
Inorganic phosphate released, causing lever arm to return to 45 degree angle (the power stroke).
-
Myosin head loses ADP.
Question 201
Answer
-
begins a few hours after death and dissapates 48-60 hours after death.
-
is caused by a lack of ATP.
-
involves myosin being "stuck" in position.
-
dissipates after thermal energy causes myosin to break down.
-
ends when enzymes involved in degradation break down myosin heads.
-
is sped up by cold.
Question 202
Answer
-
is a motor protein.
-
mostly move vesicles and organelles toward the (-) end of MTs.
-
commonly refers to Kinesin II.
-
has a heavy chain on N terminus, the motor domain.
-
is involved in superfamily of at least 14 members.
Question 203
Question
Which region of kinesin has conformational changes during ATP binding and hydrolysis?
Question 204
Question
Kinesin C terminus holds cargo.
Question 205
Question
Has a similar function and a similar sequence to myosin II.
Question 206
Question
Select the steps of mechanochemical kinesin cycle:
Answer
-
Heads work in walking motion fueled by ATP.
-
Kinesin is typically bound to ADP, which will bind weakly to MT once contact made.
-
Kinesin-ADP becomes Kinesin-ATP.
-
Kinesin ATP will bind weakly to MT. Conformational change of ATP binding causes lagging strand to zip forward 8nm.
-
ATP hydrolyzed at on new lagging head.
-
New leading strand releases ADP and binds ATP with MT.
-
Lagging strand propelled forward.
-
Cool note. MT bound tightly by kinesin ATP, just like myosin II binds tightly to actin without nucleotide.
Question 207
Answer
-
moves vesicles and organelles towards the center of the cell.
-
is involved in separation of chromatids during anaphase.
-
includes cytoplasmic dynein with 2 large head motor domains and 2 light domains.
-
includes complex axonemal dynein with 3 large heads and many light chains.
-
are the slowest motor proteins.
Question 208
Question
Dynein function:
Answer
-
large motor head in a ring at C terminal domain.
-
has 6 AAA domains, 4 of which retain ATPase activity with one primary.
-
has tail that carries cargo.
-
has long coiled-coil stalk that binds MT.
-
ATP hydrolysis causes attachment of stalk to MT.
-
release of ADP and Pi leads to the large power stroke conformational change.
-
8nm steps toward (-) of MT.
Question 209
Question
Kinesin directs vesicles and organelles to cell exterior.
Question 210
Question
Cdc42 yields large number of filopodia made of MTs.
Question 211
Question
Rac, Rho, cdc42 are small G proteins that alter actin skeleton.
Question 212
Question
Taxol kills rapidly dividing cells by stabilizing MTs.