Deck 24: Protein Trafficking

Question 1

The process by which proteins are packaged and sorted is known as ___.

Answer 1

trafficking

Question 2

Protein synthesis occurs

A) in the cytosol
B) at the surface of the endoplasmic reticulum
C) at the surface of the Golgi
D) within the nucleus
E) Both A and B are correct

Answer 2

Both A and B are correct

Question 3

Bacteria

A) do not undergo protein sorting
B) add signals directing proteins to cellular targets within the Golgi
C) may use nucleotides to signal where in the cell proteins are targeted
D) may signal proteins to the cell membrane
E) rely only on O-glycosylation to signal proteins to cell targets

Answer 3

may signal proteins to the cell membrane

Question 4

The information needed to sort proteins for trafficking resides in

A) the amino acid sequence of the protein
B) the primary structure of the protein
C) the secondary structure of the protein
D) Both A and B
E) All of the above

Question 5

To effect translation, ribosomal subunits coalesce around ___ in the ___ of the cell.

A) mRNA; cytosol
B) mRNA; rough ER membrane
C) tRNA; rough ER membrane
D) mRNA; rough ER lumen
E) mRNA; smooth ER membrane

Question 6

Signal sequences that direct proteins to their proper cellular locations are made up of

A) one monosaccharide
B) polysaccharides
C) one unusual amino acid
D) short peptides
E) a phospholipid

Question 7

Signal sequences have been found for proteins destined for the
I. mitochondrial matrix
II. chloroplast outer membrane
III. peroxisome
IV. Golgi membrane

A) I only
B) II and IV
C) III
D) I, II and III
E) II, III and IV

Question 8

Proteins acted upon by signal peptidase

A) are destined to be further processed within the ER lumen
B) travel within a vesicle to the cis Golgi
C) retain the KDEL sequence
D) Both A and B are correct
E) All of the above are correct

Question 9

Proteins destined to remain within the ER membrane are secured to the membrane via

A) their polysaccharide moieties
B) a transmembrane helix within their structure
C) a phospholipid in the lumen-side leaflet
D) a cholesterol embedded in the cytosolic-side leaflet
E) their entire structure

Question 10

Which would NOT be true of insulin within a pancreatic-cell?
I. It would retain its KDEL signal peptide
II. It would enter the Golgi with a COPI coat
III. It would enter the cis Golgi from the ER
IV. It would leave the ER with a clathrin coat

A) I only
B) I, II and III
C) III and IV
D) IV only
E) I, II and IV

Question 11

Vesicles containing newly translated DNA polymerase would travel by ___ transport after leaving the Golgi.

Question 12

Vesicles trafficked among the trans Golgi, plasma membrane and endosomal compartments are commonly surrounded by

A) COPI
B) COPII
C) clathrin
D) ER membrane
E) None of the above is correct

Question 13

Vesicular coating by COPI and COPII is energized by

A) GTP hydrolysis
B) ATP hydrolysis
C) ADP hydrolysis
D) GDP ribosylation enzyme
E) mannose-6-phosphate hydrolysis

Question 14

The outer layer of the protein coat surrounding anterograde vesicles is composed of ___, which helps make up ___.

A) Sec 13-31 proteins; COPI
B) Sec 13-31 proteins; COPII
C) Sec 23-24 proteins; COPII
D) Sec 23-24 proteins; COPI
E) Sec 23-24 proteins; clathrin

Question 15

Vesicles coated in COPI proteins depend on ADP-ribosylation factor (ARF), which is similar to ___ in COPII-coated vesicles.

A) Rabs
B) GAP
C) GEF
D) Sar1
E) GDI

Question 16

Sar1 has

A) GTPase activity
B) ATPase activity
C) kinase activity
D) phosphatase activity
E) None of the above

Question 17

In addition to assisting with proper vesicle coating, ___ are also important to ___.

A) GEFs; cell signaling
B) Rabs; motor proteins
C) GEFs; translation
D) Both A and B are correct
E) All of the above are correct

Question 18

GEFs (guanine nucleotide exchange factors) bind to Rab and block phosphorylation of GDP. When GTP is not bound to Rab, vesicular coating and transport are inhibited.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 19

Which inactivates vesicular coating and transport?

A) ARF
B) GAP
C) GDI
D) GEF
E) None of the above

Question 20

How do proteins move through the Golgi?

A) From cis to cisternae to trans
B) From cisternae to trans to cis
C) From trans to cisternae to cis
D) anterograde to retrograde
E) retrograde to anterograde

Question 21

As proteins move through the Golgi, a common post-translational modification is glycosylation. Other modifications include phosphorylation and sulfation.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 22

Addition of mannose-6-phosphate targets a protein to

A) peroxisomes
B) the smooth ER
C) lysosomes
D) the mitochondrial inner membrane
E) the chloroplast thylakoid membrane

Question 23

One protein modification that occurs in the Golgi is the addition of mannose-6-phosphate groups through ___ bonds to ___ residues.

A) O-glycosidic; asparagine
B) N-glycosidic; asparagine
C) N-glycosidic; glutamine
D) O-glycosidic; glutamine
E) O-glycosidic; KDEL

Question 24

Common to both motor proteins and DNA and RNA polymerases is

A) processivity
B) all are catalysts
C) all require GTP hydrolysis for energy
D) all generate motion
E) None of the above

Question 25

All molecular motors travel along ___ elements.

Question 26

Myosins are associated with the protein ___, while dyneins are associated with the protein ___ as they move through the cell.

Question 27

In motor proteins, the ___ determines the length of the "step" along the ___ .

A) availability of ATP; cytoskeletal element
B) availability of ATP; plasma membrane
C) availiability of GTP; cytoskeletal element
D) length of the arm; cytoskeletal element
E) length of the arm; organellar membrane

Question 28

Although not completely understood, Myosin II's light chains apparently

A) bind ATP
B) are responsible for hydrolyzing ATP
C) stabilize the head region
D) have a regulatory function
E) Both A and B are correct

Question 29

Myosin II's coiled-coil domain

A) makes up the protein's head region
B) is necessary for ATP binding
C) serves as the ATPase catalytic subunit
D) binds calcium and regulates the protein's activity
E) makes up its tail

Question 30

Like other guanine nucleotide regulatory proteins, myosin II exchanges GDP for GTP, which sets the stage for activation. Subsequent nucleotide hydrolysis by the catalytic subunit of myosin II energizes a conformational change, which ultimately results in contraction.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 31

Calcium must be present for muscle contraction to occur. Calcium

A) fits in the binding sites of actin and attracts the myosin heads
B) fits in the binding sites of actin and attracts the myosin tails
C) binds troponin, causing tropomyosin to shift and expose actin binding sites
D) binds tropomyosin, causing troponin to shift and expose actin binding sites
E) serves as a cofactor in the catalytic subunit of myosin, encouraging ATP hydrolysis

Question 32

Rigor mortis upon death is due to

A) depleted calcium availability, so actin is "frozen" away from myosin
B) calcium released from the sarcoplasmic reticulum floods the cell, causing a massive contraction event
C) actin polymers break down quickly with cell death, "freezing" the cell in place
D) depleted ATP keeps the ADP-myosin-actin complex "frozen" in its contractile state
E) depleted ATP keeps the myosin from interacting with actin, "freezing" the cell in place

Question 33

Myosin II binding to and subsequent dissociation from actin in muscle contraction is due to

A) conformational change in the myosin head
B) ATP hydrolysis followed by release of phosphate within the myosin head
C) ATP hydrolysis followed by release of phosphate within the myosin tail
D) ATP hydrolysis followed by release of phosphate within the actin binding site
E) Both A and B are correct

Question 34

The actual movement of myosin II along actin (the "power stroke" that effects contraction) occurs

A) when ATP is available to the myosin tails and is hydrolyzed
B) when ATP is available to the myosin heads and is hydrolyzed
C) when the phosphate group released following ATP hydrolysis is released from actin
D) when ADP is released from the myosin head
E) Both A and B are correct

Question 35

Apparently calcium plays a role in myosin V activity due to the presence of ___ within the myosin structure

A) the myosin head group
B) calmodulin
C) troponin
D) tropomyosin
E) globular actin subunits

Question 36

Similarities between myosin II and myosin V include
I. presence of calmodulin
II. coiled coil tail
III. head group with attachment site for actin filaments
IV. structural head group with ATPase domain

A) I only
B) II and III
C) I, II and IV
D) II, III and IV
E) I, II, III and IV

Question 37

Kinesins differ from myosin V in that

A) they move toward the growing end of the cytoskeletal element
B) they interact with tubulins that make up microtubules
C) they have a globular head domain
D) they are considered an ATPase molecular motor
E) they carry cargo

Question 38

Picturing kinesins "walking" along a microtubule, its head domains seem to act like "feet." A "step" forward is taken when the front "foot" exchanges ATP for ADP, hydrolysis occurs, and the kinesin binds to the microtubule at a site about 8 nm from its original position.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 39

Kinesin light chains
I. associate with the tails of the kinesin heavy chains
II. may associate with other proteins such as Rabs
III. associate with each other
IV. seem to act as adaptors between cargo and heavy chains

A) I and II
B) I, II and III
C) III only
D) I, II, and IV
E) I, II, III and IV

Question 40

When not needed to transport cargo, kinesin is

A) found in the cytosol
B) bound to ADP
C) has light chains phosphorylated by AMP kinase
D) Both A and B
E) All of the above

Question 41

Dyneins and kinesins are similar in that

A) both interact with microtubules
B) both have head regions that interact with the cytoskeleton element
C) both bind actin
D) both move in the retrograde direction
E) None of the above

Question 42

The dynein microtubule binding domain contains AAA ATPase domains. ATP hydrolysis leads to tighter binding of one arm of dynein, which in turn shifts the conformation of the other arm along the microtubule.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 43

Movement of very large vesicles and even organelles around the cell is mostly by

A) dynein
B) kinesins
C) myosin V
D) myosin II
E) All of the above

Question 44

Dynamin is associated with

A) clathrin
B) vesicle formation
C) endocytosis
D) Both A and B
E) All of the above

Question 45

Bacteria and some ciliated cells use ___ to generate motion.

A) actin and myosin II
B) actin and myosin V
C) F0/F1 ATPase
D) dynein
E) kinesins

Question 46

Vesicular fusion is important in moving cargo out of the cell. Targeting particular integral proteins to the plasma membrane can also be accomplished by vesicular fusion.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 47

Vesicular fusion occurs with the interaction of two classes of ___ proteins.

Question 48

SNARE proteins fall into the 'v' category (for ___) and 't' category (for ___).

Question 49

SNARE proteins have been highly characterized in

A) cardiac myocytes
B) neurons
C) hepatocytes
D) exocrine cells
E) vascular endothelium

Question 50

One of the way SNARE proteins can be tethered to lipid bilayers is through

A) palmitoylation of cysteine residues
B) palmitoylation of asparagine residues
C) eicosapentanoylation of asparagine residues
D) cysteine residues bound to cholesterol
E) asparagine residues bound to mannose

Question 51

SNAREs can be anchored to the plasma membrane via a single transmembrane helix. If this is the case, the transmembrane helix anchors the protein through both membrane leaflets.

A) Both sentences are true
B) Both sentences are false
C) The first sentence is true and the second sentence is false
D) The first sentence is false and the second sentence is true

Question 52

In the first step of vesicular binding of neurotransmitter vesicles to neuronal plasma membrane

A) synaptobrevin associated with the plasma membrane interacts with SNAP-25 and syntaxin of the vesicle
B) SNAP-25 and syntaxin associated with the plasma membrane interacts with synaptobrevin of the vesicle
C) SNAP-25 associated with the plasma membrane interacts with synaptobrevin and syntaxin of the vesicle

Question 53

In the neuron, calcium

A) binds the C2 domains of synaptogmin
B) is necessary to signal zippering of synaptobrevin to syntaxin and SNAP-25
C) binds to the core SNARE complex to activate bilayer fusion
D) assists the vesicle approaching the plasma membrane by revealing actin binding sites
E) Both A and B

Question 54

Calcium plays an important role in release of neurotransmitters. Calcium

A) is released from ER stores when the neuronal axon is depolarized
B) must bind the axon cytoskeleton to assist movement of neurotransmitter-containing vesicles toward the axon synapse
C) enters the axon through ligand-gated channels when extracellular neurotransmitters are available
D) enters the axon through voltage-gated channels when the axon is depolarized
E) None of the above is correct

Question 55

For successful vesicular fusion in neuronal axons, ___ senses calcium availability.

Question 56

The zippering hypothesis describes v-SNARE and t-SNARE interactions as forming

A) layered sheets
B) coiled coils
C) 7-helix transmembrane domains
D) GTP-ase conformational shifts
E) lipid-lipid interactions

Question 57

The coiled-coil domain that facilitates vesicular fusion in neurons

A) involves four helices
B) is found parallel to the plane of the plasma membrane
C) has a core similar to a leucine zipper
D) seems to involve glutamine and arginine interactions
E) All of the above