Deck 12: Protein Sorting and Transport

Question 1

Using radiolabeled amino acids, Palade and colleagues defined the pathway taken by secreted proteins. Which sequence represents that pathway?

A) Rough ER $\rightarrow$ smooth ER $\rightarrow$ Golgi $\rightarrow$ secretory vesicles $\rightarrow$ cell exterior
B) Rough ER $\rightarrow$ smooth ER $\rightarrow$ Golgi $\rightarrow$ endosomes $\rightarrow$ cell exterior
C) Rough ER $\rightarrow$ Golgi $\rightarrow$ lysosomes $\rightarrow$ cell exterior
D) Rough ER $\rightarrow$ Golgi $\rightarrow$ secretory vesicles $\rightarrow$ cell exterior

Answer 1

Rough ER $\rightarrow$ Golgi $\rightarrow$ secretory vesicles $\rightarrow$ cell exterior

Question 2

Most plasma membrane proteins in higher eukaryotic cells are synthesized on

A) free ribosomes and inserted after translation into the plasma membrane.
B) rough ER ribosomes and carried to the plasma membrane by vesicles that pinch off from the Golgi apparatus.
C) rough ER ribosomes and carried to the plasma membrane by vesicles that pinch off from the rough ER.
D) ribosomes associated with the plasma membrane and inserted into the membrane cotranslationally.

Answer 2

B

Question 3

A signal sequence in a polypeptide chain targets all but _______ proteins to the rough ER surface.

A) secreted
B) plasma membrane
C) mitochondrial
D) lysosomal

Answer 3

C

Question 4

Free ribosomes in the cytosol and ribosomes bound to the ER membrane have

A) different types of large and small subunits.
B) the same types of large and small subunits.
C) different types of large subunits but the same small subunits.
D) different types of small subunits but the same large subunits.

Question 5

When compared to polypeptides synthesized in vitro on free ribosomes, polypeptides synthesized from the same mRNA on microsome-bound ribosomes often are

A) the same size.
B) larger.
C) smaller.
D) more hydrophobic.

Question 6

As they emerge from the ribosome, signal sequences are recognized and bound by

A) a tRNA.
B) a signal peptidase.
C) a signal recognition particle (SRP).
D) an SRP receptor.

Question 7

Which statement describes evidence that supports the signal hypothesis as an explanation for how secretory proteins are targeted to the rough ER?

A) The protein is larger when synthesized in vitro on free polysomes.
B) The secretory protein ends up in the cytosol when a short sequence is deleted by genetic engineering.
C) A normally cytosolic protein is secreted when a specific sequence is added to it by genetic engineering.
D) All of the above

Question 8

If secretory proteins are isolated from secretory vesicles and injected into the cytosol, they will

A) be taken up into the rough ER and follow the secretory pathway.
B) remain in the cytosol until they are degraded.
C) be secreted through channels in the plasma membrane.
D) be taken up into secretory vesicles and secreted.

Question 9

The signal sequence that targets a nascent polypeptide and its mRNA to the rough ER is rich in _______ amino acids.

A) positively charged
B) negatively charged
C) hydrophilic
D) hydrophobic

Question 10

Protein folding in the ER is assisted by a chaperone called

A) BiP.
B) PiP.
C) Hsp60.
D) Hsp90.

Question 11

Disulfide bonds within or between proteins form easily

A) in the ER but not the cytosol.
B) in neither the cytosol nor the ER.
C) in the cytosol but not the ER.
D) in both the cytosol and the ER.

Question 12

GPI-anchored proteins are synthesized

A) on free ribosomes and attached to the GPI group on the outside of the ER.
B) as transmembrane proteins, then are cleaved and joined to the GPI group on the cytosolic surface of the ER.
C) as transmembrane proteins, then are cleaved and joined to the GPI group on the lumenal surface of the ER.
D) on free ribosomes and attached to the GPI group on the cytosolic surface of the ER.

Question 13

Proteins attached to the outer half of the plasma membrane bilayer are usually attached by a

A) farnesyl tail.
B) prenyl tail.
C) geranyl tail.
D) glycosylphosphatidylinositol (GPI) anchor.

Question 14

The unfolded protein response involves

A) translation of most proteins.
B) increased synthesis of chaperones.
C) decreased proteasome activity.
D) All of the above

Question 15

Most cellular lipids are synthesized in

A) fat droplets.
B) mitochondria.
C) the endoplasmic reticulum.
D) the Golgi apparatus.

Question 16

Newly synthesized membrane lipids are found in both halves of a membrane bilayer because they are

A) synthesized on one surface and flipped to the other surface by flippases.
B) removed and transported to these locations by lipid transport proteins.
C) synthesized on one surface and flipped spontaneously to the other surface.
D) synthesized on both surfaces.

Question 17

The sequence Lys-Asp-Glu-Leu (KDEL) serves as an ER retention signal for proteins by binding to KDEL receptors that

A) hold the proteins in the rough ER.
B) hold the proteins in the smooth ER.
C) hold the proteins in both the smooth ER and rough ER and prevent their transport to the Golgi apparatus.
D) transport the proteins from the Golgi apparatus back to the ER.

Question 18

Vesicles enter the Golgi apparatus by fusing with _______, and they exit from the _______.

A) the cis (convex) face; trans (concave) face
B) the trans (concave) face; cis (convex) face
C) both the cis (convex) and the trans (concave) faces; sides of cisternae
D) the sides of the cisternae; cis (convex) face

Question 19

N-linked oligosaccharides are added in the _______ and modified in the _______.

A) ER; Golgi
B) cis Golgi; medial Golgi
C) medial Golgi; trans Golgi
D) cis Golgi; trans Golgi

Question 20

Which of the following polysaccharides is synthesized in the Golgi apparatus?

A) Pectin
B) Cellulose
C) Amylose
D) Glycogen

Question 21

Which of the following proteins do not pass through the Golgi apparatus?

A) Lysosomal enzymes
B) Cell surface proteins
C) Ribosomal proteins
D) Proteins secreted by exocytosis

Question 22

Which of the following vesicle types does not bud directly from the trans-Golgi network?

A) Vesicles transporting plasma membrane receptors
B) Vesicles that form regulated secretory vesicles
C) Vesicles carrying lysosomal enzymes
D) Lysosomes

Question 23

Lysosomal proteins are marked by the addition of a phosphate to a _______ group.

A) glucose
B) serine
C) GDP
D) mannose

Question 24

Plasma membrane proteins of intestinal epithelial cells require separate targeting to

A) one continuous plasma membrane domain.
B) two plasma membrane domains: the apical and basolateral.
C) three plasma membrane domains: the apical, lateral, and basal.
D) four plasma membrane domains: one apical, two lateral, and a basal.

Question 25

In plant cells, vesicles transport proteins from the Golgi apparatus to

A) lysosomes.
B) vacuoles.
C) chloroplasts.
D) mitochondria.

Question 26

In polarized epithelial cells, membrane proteins containing a dileucine (LL) motif in their cytoplasmic domain are

A) retained in the Golgi apparatus.
B) targeted to lysosomes.
C) targeted to the basolateral plasma membrane.
D) targeted to the apical plasma membrane.

Question 27

Clathrin coats are bound to specific receptors by a protein called

A) an adaptor protein.
B) ARF.
C) COPI.
D) NSF.

Question 28

Arf function on vesicles is regulated by

A) phosphorylation of serine residues.
B) phosphorylation of mannose residues.
C) binding of GTP.
D) binding of ATP.

Question 29

The pinching off of budding clathrin-coated vesicles is driven by the action of

A) dynamin and GTP hydrolysis.
B) dynamin and ATP hydrolysis.
C) GDP bound ARF.
D) GTP bound ARF.

Question 30

Which coat protein(s) would you expect to be recruited for vesicle formation by a KDEL receptor?

A) COPI.
B) COPII.
C) clathrin.
D) COPI and clathrin.

Question 31

Which coat protein directs retrograde vesicular transport from the ERGIC or Golgi to the endoplasmic reticulum?

A) COPII
B) COPI
C) clathrin
D) Both COPI and COPII

Question 32

Vesicles that carry proteins from the rough ER to the Golgi apparatus bud off as _______ vesicles.

A) uncoated
B) clathrin-coated
C) COPI-coated
D) COPII-coated

Question 33

Lysosomal proteins are initially incorporated into _______ vesicles.

A) uncoated
B) clathrin-coated
C) COPI-coated
D) COPII-coated

Question 34

How many Rab proteins have been shown to play a specific role in vesicular transport?

A) fewer than 10
B) about 25
C) about 50
D) 60 or more

Question 35

Lysosomes digest

A) proteins only.
B) nucleic acids and proteins only.
C) carbohydrates only.
D) proteins, nucleic acids, and carbohydrates.

Question 36

The pH inside lysosomes is about

A) 7.0.
B) 6.0.
C) 5.0.
D) 4.0.

Question 37

Gaucher disease results from the failure of macrophage lysosomes to hydrolyze

A) proteins.
B) glycolipids.
C) DNA.
D) polysaccharides.

Question 38

Transport vesicles carrying acid hydrolases fuse with

A) lysosomes.
B) endocytic vesicles.
C) early endosomes.
D) late endosomes.

Question 39

In eukaryotic cells, most protein synthesis is initiated in the _______.

Question 40

The cytosolic surface of the rough endoplasmic membrane can be readily distinguished from the luminal surface by the presence of _______.

Question 41

Proteins are targeted to the endoplasmic reticulum by a _______ that binds to a(n) _______.

Question 42

Cotranslational transport of proteins across the endoplasmic reticulum membrane occurs through a protein channel called the _______.

Question 43

Because of the oxidizing environment of the ER lumen, the formation of _______ bonds is a frequent event.

Question 44

Proteins that fail to fold properly in the endoplasmic reticulum are removed through the process of _______.

Question 45

The transcription factors that direct the unfolded protein response are _______ and _______.

Question 46

Membrane lipid biosynthesis occurs in the _______ endoplasmic reticulum.

Question 47

Cargo protein transport between different organelles in the secretory pathway occurs by _______-mediated transport.

Question 48

In cisternal maturation, the carriers for cargo protein transport through the Golgi apparatus are the Golgi _______.

Question 49

During cargo protein transport through the Golgi apparatus, N-linked oligosaccharide side chains are processed from high-_______ to _______ acid-rich.

Question 50

Adaptor proteins are involved in the selection of _______ to be incorporated into coated vesicles.

Question 51

The three major classes of vesicle coat proteins are _______, _______, and _______.

Question 52

Vesicle fusion is mediated by the formation of protein complexes between vesicle and target _______.

Question 53

Proteins destined for degradation are delivered to lysosomes by two processes: _______ and _______.

Question 54

Defects in lysosomal enzyme levels can be corrected by _______ replacement therapy.

Question 55

The major function of the hydrophobic sequence at the amino terminals of proteins that are to be secreted from eukaryotic cells is to target those proteins to the rough ER.

Question 56

Polypeptides inside the ER are usually smaller than polypeptides synthesized from the same mRNA that have not entered the ER.

Question 57

Transmembrane proteins in the plasma membrane are synthesized on the rough ER.

Question 58

A newly synthesized polypeptide chain enters the ER through a translocon.

Question 59

The initial site of N-linked glycosylation is the Golgi apparatus.

Question 60

Phospholipids are synthesized in the cytosolic half of the ER bilayer.

Question 61

Smooth ER is abundant in cells actively synthesizing steroid hormones.

Question 62

The Golgi apparatus is the main site of intracellular drug detoxification.

Question 63

Vesicle formation is driven by the binding of clathrin or COP proteins.

Question 64

Synaptic vesicles use a special mode of fusion that is completely different from regulated secretion in a typical secretory cell.

Question 65

The main method by which a cell gets rid of old, worn-out organelles is exocytosis.

Question 66

Describe the role of each of the following in targeting and processing proteins in the endoplasmic reticulum.

-A signal sequence

Question 67

Describe the role of each of the following in targeting and processing proteins in the endoplasmic reticulum.

-A signal recognition particle (SRP)

Question 68

Describe the role of each of the following in targeting and processing proteins in the endoplasmic reticulum.

-A signal peptidase

Question 69

Describe the role of each of the following in targeting and processing proteins in the endoplasmic reticulum.

-Protein disulfide isomerase

Question 70

Describe the role of each of the following in targeting and processing proteins in the endoplasmic reticulum.

-A KDEL sequence

Question 71

What happens to a glycoprotein in the ER lumen if it cannot be folded correctly?

Question 72

What is the function of the trans-Golgi network?

Question 73

In polarized epithelial cells, proteins may be specifically targeted to what two membrane domains?

Question 74

What are the two families of small GTP-binding proteins that are involved in the formation of coated vesicles?

Question 75

What are Rab proteins?

Question 76

What roles do SNAREs play in the specific binding and fusion of vesicles to a target membrane?

Question 77

What deficiency causes I-cell disease?

Question 78

What is the likely transport pathway for lysosomal hydrolases in patients with I-cell disease?

Question 79

How do lysosomes become acidic?

Question 80

How do hydrolytic enzymes get from the Golgi apparatus to lysosomes?