chap15

Question 1

Eukaryotic cells contain many membrane-enclosed _, including a nucleus, an endoplasmic reticulum (ER), a Golgi apparatus, lysosomes, endosomes, mitochondria, chloroplasts (in plant cells), and _. The ER, Golgi apparatus, peroxisomes, endosomes, and lysosomes are all part of the _

Answer 1

organelles
peroxisomes
endomembrane system.

Question 2

Most organelle proteins are made in the _ and transported into the _ where they function. _ in the amino acid sequence guide the proteins to the correct _; proteins that function in the cytosol have _ and _

Answer 2

cytosol
organelle
Sorting signals
organelle
no such signals
remain where they are made.

Question 3

Nuclear proteins contain _ that help direct their active transport from the cytosol into the nucleus through _, which penetrate the _ of the nuclear envelope. The proteins are transported in _ conformation.

Answer 3

nuclear localization signals
nuclear pores
double membrane
their fully folded

Question 4

Most mitochondrial and chloroplast proteins are made in the _ and are then transported into the _ by _ in their membranes. The proteins are _ during the transport process.

Answer 4

cytosol
organelles
protein translocators
unfolded

Question 5

The ER makes most of the cell’s _ and many of its _. The proteins are made by _ that are directed to the _ by a _ in the cytosol that recognizes an _ on the growing polypeptide chain (protein being synthesized at the same time). The _ complex binds to a _ on the _ membrane, which passes the ribosome to a _ that _ the growing polypeptide across the _

Answer 5

lipids
proteins
ribosomes
ER
signal-recognition particle (SRP)
ER signal sequence
ribosome– SRP
receptor
ER
protein translocator
threads
ER membrane.

Question 6

Water-soluble proteins destined for _ or for the _ of the endomembrane system pass _ into the _, while transmembrane proteins destined for either the _ of these organelles or for the _ remain _ in _ by one or more _

Answer 6

secretion
lumen of an organelle
completely
ER lumen
membrane
plasma membrane
anchored
the lipid bilayer
membrane-spanning α helices.

Question 7

In the ER lumen, proteins fold up, _ with their protein partners, form _ bonds, and become decorated with _ chains.

Answer 7

assemble
disulfide
oligosaccharide

Question 8

The disulfide bonds help to _ of proteins that will encounter _ enzymes and changes in _ outside the cell

Answer 8

stabilize the structure
degradative
pH

Question 9

The oligosaccharides on proteins can serve various functions. They can protect a protein from _, hold it in the _ until it is _, or help _ it to the _ by serving as a _ signal for _ the protein into appropriate transport vesicles.

Answer 9

degradation
ER
properly folded
guide
appropriate organelle
transport
packaging

Question 10

_ is an important quality-control step; proteins that either fail to fold properly or fail to _ are _ by _ proteins, which _; proteins that still fail to fold or assemble are _.

Answer 10

Exit from the ER
assemble with their normal partners
retained in the ER
chaperone
prevent their aggregation and help them fold
_
transported to the cytosol, where they are degraded
_

Question 11

Excessive accumulation of misfolded proteins triggers an _ that _ the ER, increases its _, and _ protein synthesis.

Answer 11

unfolded protein response (UPR)
expands
capacity to fold new proteins properly
reduces

Question 12

Protein transport from the ER to the _ and from the _ to other destinations is mediated by _ that _ off from one membrane and _ with another, a process called _

Answer 12

Golgi apparatus
Golgi apparatus
transport vesicles
continually bud
fuse
vesicular transport.

Question 13

Budding transport vesicles have distinctive _ proteins on their _ surface; the assembly of the _ helps drive both the _ process and the _, with _, into the forming vesicle.

Answer 13

coat
cytosolic
coat
budding
incorporation of cargo receptors
their bound cargo molecules

Question 14

Coated vesicles rapidly lose their _, enabling them to _ and then _ with a particular target _; _ are mediated by _ and target membrane, including _, _, and _ proteins.

Answer 14

protein coat
dock
fuse
membrane
docking and fusion
proteins on the surface of the vesicle
Rab
tethering
SNARE

Question 15

The _ receives _ proteins from the ER; it modifies their _, _ the proteins, and _ them from the _ network to the plasma membrane, lysosomes (via endosomes), or secretory vesicles.

Answer 15

Golgi apparatus
newly made
oligosaccharides
sorts
dispatches
trans-Golgi

Question 16

In all eukaryotic cells, transport vesicles continually bud from the _ and fuse with the _; this process of constitutive _ delivers proteins to the cell surface for secretion and _ lipids and proteins _.

Answer 16

trans-Golgi network
plasma membrane
exocytosis
incorporates
into the plasma membrane

Question 17

Specialized secretory cells also have a _ pathway, in which molecules _ in secretory vesicles are released from the cell by _ when _.

Answer 17

regulated exocytosis
concentrated and stored
exocytosis
the cell is signaled to secrete

Question 18

Cells ingest fluid, molecules, and sometimes even particles by _, in which regions of plasma membrane _ and _ to form endocytic vesicles.

Answer 18

endocytosis
invaginate (clathrin-coated)
pinch off (Dynamin)

Question 19

Much of the material that is endocytosed is delivered to _, which mature into _, in which the material is _ by _; most of the components of the endocytic vesicle membrane, however, are _ back to the plasma membrane for reuse.

Answer 19

endosomes
lysosomes
degraded
hydrolytic enzymes
recycled in transport vesicles

Question 20

Membrane-enclosed organelles import proteins by one of three mechanisms.

Answer 20

TRANSPORT THROUGH NUCLEAR PORES
TRANSPORT ACROSS MEMBRANES
TRANSPORT BY VESICLES

Question 21

_ direct proteins to the correct destination.

Answer 21

Signal sequences

Question 22

Proteins destined for the ER possess
an _ that directs them to that organelle, whereas those destined to remain in the cytosol _

Answer 22

N-terminal signal sequence
lack any such signal sequence.

Question 23

The nuclear pore complex forms a gate through which _ macromolecules and larger complexes enter or exit the nucleus.

Answer 23

selected

Question 24

Protein _ protrude from both sides of the pore complex; on the nuclear side, they _ to form a _ structure. The spacing between the fibrils is _ that the fibrils _ obstruct access to the pores.

Answer 24

fibrils
converge
basketlike
wide enough
do not

Question 25

A _ is used to synthesize all the proteins encoded by the nuclear genome.

Answer 25

common pool of ribosomes

Question 26

Ribosomes that are translating proteins
with _ remain _.

Answer 26

no ER signal sequence
free in the cytosol

Question 27

Ribosomes that are translating proteins containing an _ on the growing polypeptide chain will be _.

Answer 27

ER signal sequence
directed to the ER membrane

Question 28

Many ribosomes bind to each mRNA molecule, forming a _.

Answer 28

polyribosome

Question 29

At the end of each round of protein synthesis, the ribosomal subunits are _ and rejoin the _.

Answer 29

released
common pool in the cytosol

Question 30

An ER signal sequence and an SRP direct a _ to the _ membrane.

Answer 30

ribosome
ER

Question 31

The SRP (brown) binds to _, thereby slowing protein _ by the ribosome.

Answer 31

_
both the exposed ER signal sequence and the ribosome
_
synthesis

Question 32

The _ then binds to an SRP receptor (dark blue) in the _ membrane. The SRP is _, and the ribosome passes from the SRP receptor to a _ in the _ membrane. Protein _ resumes, and the _ starts to transfer the growing polypeptide across the lipid bilayer.

Answer 32

SRP–ribosome complex
ER
released
protein translocator
ER
synthesis
translocator

Question 33

At some point during the translocation process, the signal peptide is cleaved
from the growing protein by a _.
Once protein synthesis is complete, the translocated polypeptide is released as a _ into the ER lumen, and the protein translocator _.

Answer 33

signal peptidase
soluble protein
closes

Question 34

An N-terminal ER signal sequence (red ) initiates transfer. In addition to this sequence, the protein also contains
a second _ sequence, which acts as a _ (orange). When this sequence enters the protein translocator, the growing polypeptide chain is discharged into the lipid bilayer. The N-terminal signal sequence is _, leaving the transmembrane protein _ in the membrane (Movie 15.4). Protein synthesis on the cytosolic side then _

Answer 34

hydrophobic
stop-transfer sequence
cleaved off
anchored
continues to completion.

Question 35

The extracellular space and each of the membrane-enclosed compartments (shaded gray) communicate with one another by means of _

Answer 35

transport vesicles

Question 36

_ vesicles transport selected cargo molecules.

Answer 36

Clathrin-coated

Question 37

_ receptors, with their bound _ molecules, are captured by _, which also bind _ molecules to the _ surface of the budding vesicle.

Answer 37

Cargo
cargo
adaptins
clathrin
cytosolic

Question 38

In flies that produce a mutant dynamin protein, clathrin-coated pits assemble and dynamin is recruited around the neck of budding vesicles but fail to pinch them off, as can be seen in this electron micrograph of the plasma membrane in a fly’s nerve ending. Flies with this mutation become paralyzed, because clathrin-mediated endocytosis grinds to a halt, preventing
the_ needed to _

Answer 38

recycling of vesicles
release neurotransmitters

Question 39

A filamentous _ protein (green) on a membrane binds to
a _ protein (yellow) on the surface of a vesicle.

Answer 39

tethering
Rab

Question 40

A _-SNARE (red) on the vesicle then binds to a complementary _-SNARE (blue) on
the target membrane.

Answer 40

v
t

Question 41

Materials destined for degradation in lysosomes follow different pathways to the lysosome.
_, _, and _ can fuse with either lysosomes or _, both of which contain _.

Answer 41

Early endosomes
phagosomes
autophagosomes
late endosomes
acid-dependent hydrolytic enzymes