bsc300 exam 3 dr. jenny

Which location can a newly synthesized protein be delivered?

a. the cytosol

b. various membrane-bound organelles

c. the cell surface

all of the answers are correct

Which can be transported into or out of the nucleus via nuclear pores?

a. proteins

b. mRNAs

c. tRNAs

d. ribosomal subunits

all of the answers are correct

A typical mammalian cell contains up to _____ different kinds of proteins.

10,000

Which are important protein-folding catalysts in the ER lumen?

peptidyl-prolyl-isomerases

The _____ contains a central channel lined with hydrophobic residues that allows transit of an unfolded protein chain while remaining sealed to ions and small hydrophilic molecules.

translocon

Which statement is FALSE?

a. Disulfide bonds are formed and rearranged by proteins in the ER lumen.

b. Oligosaccharide side chains may promote folding and stability of glycoproteins.

c. Chaperones and other ER proteins facilitate folding and assembly of proteins.

d. Improperly folded proteins in the ER induce expression of protein-folding catalysts.

e. A preformed N-linked oligosaccharide is added to many proteins in the smooth ER.

A preformed N-linked oligosaccharide is added to many proteins in the smooth ER.

The delivery of newly synthesized proteins to their proper destinations is referred to as:

protein targeting or sorting

Which process occurs in the ER?

a. protein modifications

b. protein folding

c. quality control for protein folding

all of the answers are correct

When cells are homogenized, the rough ER breaks up into small closed vesicles with ribosomes on the outside, otherwise known as:

microsomes

Which is NOT a pathway or part of a pathway used to transport proteins from the stroma into the thylakoid of chloroplasts?

a. a chloroplast SRP-dependent pathway

b. a protein related to bacterial protein SecA

c. targeting proteins to the thylakoid membrane

d. thylakoid proteins that bind metal-containing cofactors, following another pathway in the thylakoid lumen

All of these are pathways used to transport proteins from the stroma into the thylakoid of chloroplasts.

Which statement is FALSE?

Proteins destined for the peroxisomal membrane contain the same targeting sequences as peroxisomal matrix proteins and are imported by the same pathways.

MOST mitochondrial and chloroplast proteins are:

a. encoded by nuclear genes.

b. synthesized on cytosolic ribosomes.

c. imported post-translationally into the organelles.

all of the answers are correct

The _____ on a nascent secretory protein is located at the N-terminus and contains a sequence of hydrophobic amino acids.

ER signal sequence

Which proteins have a cleavable N-terminal ER signal sequence?

type I proteins

The majority of mammalian proteins are synthesized by:

cytosolic ribosomes

A protein sorting process known as _____ involves transport of proteins from the ER to their final destination within membrane-enclosed vesicles.

the secretory pathway

Which process is a principal modification that membrane and soluble secretory proteins synthesized on the rough ER undergo?

a. covalent addition and processing of carbohydrates in the ER and Golgi

b. formation of disulfide bonds in the ER

c. proper folding of polypeptide chains and assembly of multi-subunit proteins in the ER

d. specific proteolytic cleavages in the ER, Golgi, and secretory vesicles

all of the answers are correct

The portion of the ER that receives proteins entering the secretory pathway is known as the:

rough ER

All vesicles use the same general mechanisms for:

a. budding.

b. selection of cargo molecules.

c. fusion with the appropriate target membranes.

All of the answers are correct.

The KKXX signal that targets proteins to COPI vesicles must be located on:

the C-terminus of the recruited protein.

The outer surface of a lipoprotein is:

water soluble

VAMP is a type of _____ protein incorporated into secretory vesicles as they bud from the cis-Golgi.

v-SNARE

Which would you expect to see packaged in a COPII vesicle?

a. proteins destined for the Golgi

b. proteins destined for the cell surface

c. proteins destined for lysosomes

d. vesicle components such as v-SNAREs

All of the answers are correct.

The interior of an LDL lipoprotein is packed mainly with:

cholesterol esters

imagine you have a yeast mutant that has a defect that prevents fusion of transport vesicles with the Golgi apparatus. where would secretory proteins build up?

in ER to golgi transport vesicles

How are cargo proteins recruited to COPII vesicles?

through interaction of a diacidic sorting signal in the cargo protein's cytosolic domain with sec 24

The acidic pH of the _____ causes most receptor-ligand complexes to dissociate.

late endosome

Lysosomal digestive enzymes include:

a. proteases.

b. glycosidases.

c. phosphatases.

d. lipases.

all of the answers are correct

All vesicles whose coats contain AP1, AP2, AP3, or GGA complexes use _____ to initiate coat assembly on the donor membrane.

ARF

The LDL receptor makes a round trip in and out of the cell interior about every:

10-20 min

Which of these findings provides evidence that dissociation of SNARE complexes requires the assistance of other proteins?

In vitro studies of systems depleted of particular cytosolic proteins, vesicles accumulated and did not fuse with target membranes.

These adapter molecules determine which cargo molecules are included in a budding transport vesicle.

a. AP1

b. AP2

c. AP3

d. GGA

all of the answers are correct

Receptor-mediated endocytosis generally occurs via:

clathrin/AP2-coated pits and vesicles.

In a classic experiment, researchers injected radioactive amino acids into the pancreas of hamsters. At different times after injection, the animals were sacrificed and the cellular locations of radioactive proteins were determined using autoradiography. Which of the following cell compartments would be radioactively labeled after the SHORTEST wait times after injection?

the ER

MOST soluble ER proteins have a _____ signal at their C-terminus.

KDEL

The major function of lysosomes is to:

degrade extracellular materials taken up by the cell and intracellular components under certain conditions.

This unifying principle governs all protein trafficking in the secretory and endocytic pathways.

a. Transport of membrane and soluble proteins is mediated by transport vesicles.

b. Cargo proteins are collected in buds arising from the membrane of one of the compartments involved in the transport.

c. Delivery of cargo proteins requires membrane fusion.

d. As transport vesicles bud from one membrane and fuse with the next, the same face of the membrane always faces the cytosol.

all of the answers are correct

Why are ER resident proteins such as BiP and disulfide isomerase often found in vesicles destined for the cis-Golgi?

Their sheer abundance causes them to be passively loaded into COPII vesicles.

In one of the initial experiments related to receptor-mediated endocytosis, Goldstein et al. used ferritin-labeled LDL particles. Why did they label their particles with ferritin?

The iron bound to ferritin allowed the researchers to visualize the cell locations of the LDL particles using electron microscopy.

Which statement is TRUE?

a. It is not possible to have both regulated and constitutive secretion in the same cell.

b. All cells exhibit both constitutive and regulated secretion.

c. Only some cells exhibit constitutive secretion, while all cells exhibit regulated secretion.

d. Only some cells exhibit regulated secretion, while all cells exhibit constitutive secretion.

e. Constitutive secretion involves secretory vesicles, whereas regulated secretion does not.

Only some cells exhibit regulated secretion, while all cells exhibit constitutive secretion.

Proteins bearing the signal sequence KDEL bind tightly to their receptor in the Golgi and are released from the receptor in the ER. How does this happen?

The binding affinity of the KDEL receptor is sensitive to pH, which is lower in the Golgi and higher in the ER.

What limits the rate at which a ligand can be internalized into a particular cell type?

the number of ligand receptors on the cell surface

What is the function of Rab GTPases?

They control the docking of vesicles on target membranes.

Where does proteolytic maturation of proproteins such as proinsulin occur?

in vesicles carrying proteins from the trans-Golgi network to the cell surface, lysosomes, and late endosomes

Which part of the LDL-receptor protein interacts with apoB-100?

the N-terminal region containing seven cysteine-rich repeats

How do proteins return to the ER from the Golgi?

through retrograde Golgi to ER transport

As part of the mechanism by which LDL receptor-ligand complexes are targeted to clathrin-coated pits, the NPXY sorting signal binds _____ to _____.

the LDL-receptor protein; the AP2 complex

_____ couple(s) a cycle of binding and hydrolysis to the formation and then dissociation of the COPII coat.

Sar1

The endocytic pathway delivers some ligands to _____ for degradation.

lysosomes

Which vesicles transport proteins from the plasma membrane and the cis-Golgi network to the late endosomes?

clathrin

This is a flattened membrane compartment formed in the second stage of the secretory pathway when anterograde transport vesicles fuse with one another.

cis-golgi cisterna

Which vesicle fuses with the lysosome?

late endosome

In pure form, these proteins can spontaneously assemble into a cage-like structure. Thus, it is thought that _____ form the scaffold for COPII vesicles.

sec 13 and sec 31

The secretory pathway operates in two stages. The first stage takes place in:

the rough ER

Which of these cell compartments has the LOWEST internal pH?

late endosome

Which process is used to facilitate the mass transfer of lipids between cells?

lipoprotein carriers

Protein aggregation within the cis-Golgi network may play a role in sorting secreted proteins:

to storage vesicles in the regulated secretory pathway.

Mature endosomes containing numerous vesicles in their interior are usually called:

multivesicular endosomes or bodies

Which transport method retrieves missorted ER-resident proteins from the cis-Golgi to correct sorting mistakes?

COPI-mediated retrograde transport

Why do individuals with familial hypercholesterolemia have elevated plasma LDL levels?

a. They are unable to synthesize the LDL-receptor protein.

b. They have defective LDL-receptor proteins.

c. They have a mutation that results in abnormal folding of the LDL receptor in the ER, leading to premature degradation of the protein.

d. They produce a version of the LDL-receptor protein that can bind normally to LDL but cannot internalize LDL particles.

all of the answers are correct

Which protein(s) control(s) polymerization of coat proteins, the initial step in vesicle budding?

ARF

The COPI coat is formed from large cytoplasmic complexes called:

coatomers

These complexes fill the space between a clathrin lattice and a vesicle membrane.

a. AP1 complexes

b. AP2 complexes

c. AP3 complexes

d. GGA

all of the answers are correct

Based on the number of v-SNARE and t-SNARE proteins identified in yeast, about how many different types of v-SNARE and t-SNARE proteins would you expect are expressed in a typical eukaryotic cell?

more than 20

The coat proteins associated with COPII vesicles include:

Sec 23/Sec24 and Sec 13/Sec31 complexes and Sec 16.

The LDL receptor-ligand complex does NOT appear in this cell compartment.

lysosome

Receptor-mediated endocytosis generally occurs via:

clathrin/AP2-coated pits and vesicles.

Specific sorting signals in membrane and luminal proteins of donor organelles interact with _____, thereby recruiting cargo proteins to vesicles.

coat proteins during vesicle budding

Where does the LDL receptor dissociate from the LDL particle?

late endosome

This evidence suggests that clathrin/AP2 complexes play a role in delivering proteins to the lysosome for degradation.

There are proteins associated with the clathrin/AP2 complex that bind ubiquitin.

Vesicle-mediated trafficking that moves proteins from the cis-Golgi to the plasma membrane utilizes vesicles with these kinds of coat proteins.

Researchers have not yet identified the coat proteins for these vesicles.

RabċGDP is tethered to the vesicle membrane via a(n):

isoprenoid anchor.

Which is an example of a secreted protein?

a. digestive enzymes

b. peptide hormones

c. serum proteins

d. collagen

all of the answers are correct

cell drinking

pinocytosis

synthesis of secreted proteins, integral plasma-membrane proteins, and proteins destined for the ER, golgi complex, plasma membrane, or lysosome begins on:

cytosolic ribosomes

a signal sequence, SRP, and SRP receptor system docks the ribosome on a(n) ________________ and cotranslationally inserts the nascent protein into or through the ER membrane

ER translocon

a signal sequence, SRP, and SRP receptor system docks the ribosome on an ER translocon and cotranslationally inserts the nascent protein into or through the:

ER membrane

where are all nuclear DNA-encoded mRNAs translated?

on cytosolic ribosomes

occurs specifically during translation or soon after synthesis

protein targeting/sorting

step one (nonsecretory pathways)

synthesis of proteins lacking an ER signal (targeting) sequence is completed on free ribosomes

step 2 (nonsecretory pathways)

proteins that contain no targeting sequence remain in the cytosol

steps 3-6 (nonsecretory pathways)

proteins with an organelle specific targeting sequence are imported from the cytosol into mitochondria, chloroplasts, peroxisomes, or the nucleus

imported and localized in multiple organelle compartments by several mechanisms

mitochondrial and chloroplast proteins

enter and exit through pores in the nuclear envelope

nuclear proteins

step 1 (secretory pathway)

ribosomes initiate nascent protein synthesis in the cytosol

step 2 (secretory pathway)

ER signal sequence direct ribosome docking onto rough ER import apparatus. nascent proteins translocated into the ER lumen or embedded in the ER membrane

step 3 (secretory pathway)

proteins in the ER membrane or lumen can move via transport vesicles to the golgi complex

step 4a or 4b (secretory pathway)

further sorting of proteins to the plasma membrane or to lysosomes in vesicles

comprises a network of membranes that penetrates much of the cytoplasm

endoplasmic reticulum

like other organelles, what is highly dynamic undergoing continual turnover and reorganization?

the ER

two subcompartments of the endoplasmic reticulum

rough and smooth

the composition of the lumenal or cisternal space inside ER membranes is the same as the surrounding cytosolic face

false

flattened sacs

cisternae

composed of a network of flattened sacs

rough ER

continuous with the outer membrane of the nuclear envelope

rough ER

has ribosomes on its cytosolic surface

rough ER

different types of cells have different ratios of the two types of ER, depending on:

activities of the cell

ribosomes attached to the rough ER:

actively synthesize proteins

extensively developed in a number of cell types

smooth Er

Many different collagen types exist, each with their own specific and sometimes unique function. The different types of collagen are called:

isoforms