Cell Biology Chapters 8 & 9

what are the differences between early and late endosomes?

-Early endosomes exchange their Rab5 proteins for Rab7 proteins as they transform into late endosomes. -Late endosomes have a population of vesicles crowding their interior; early endosomes do not. -Late endosomes exhibit a lower pH than early endosomes. -In late endosomes, the outer boundary membrane has budded inward on its lumenal surface creating a group of vesicles.

What is the minimum number of kinesin heads in contact with a microtubule at all times?

1

In a normal microtubule, how many protofilaments make up its cylindrical wall?

13

Which pH below would be most likely to favor the operation of a lysosomal enzyme?

4.5

Which GTP-binding protein is associated with clathrin-coated vesicles and helps to initiate the formation of the coat?

ARF1 (adenosylation ribose factor)

From where does the energy to run myosin motors come?

ATP

The energy source for the molecular motors dynein, kinesin and myosin is __________.

ATP

Which of the following is a function performed by the cytoskeleton?

All of the choices are correct. Option B: serves as a force-generating apparatus that moves cells from one place to another Option C: positions various organelles within the cell interior Option D: provides structural support that determines cell shape and resists deforming forces Option E: provides a network of tracks over which materials like mRNA and organelles move within cells

Eventually, it was discovered that in order to facilitate actin filament nucleation in Listeria, ActA must interact transiently with another protein and stimulate its nucleation activity. What is the name of the protein with which ActA interacts to accomplish this feat?

Arp2/3

Where does glycosylation take place? 1) Lysosomes 2) Golgi Complex 3) Rough Endoplasmic Reticulum

Both 2 and 3 are correct

Which coated vesicles move materials in a retrograde direction from the ERGIC and Golgi stack backwards toward the ER?

COPI-coated vesicles

You inject labeled keratin subunits into cultured skin cells. What happens a few minutes later?

Filaments become labeled at sites scattered throughout their length, rather than at their ends.

What happens to the clathrin coat once the vesicle has budded from the Golgi body?

It is lost.

_____________ residues act as an "address" for delivery of proteins to lysosomes

Mannose 6-phosphate

The current model for the nucleation of microtubules is that a helical array of gamma-tubulin subunits forms an open, lock-washer-like ring-shaped template upon which the first row of alpha-beta-tubulin dimers assembles. How does this model account for the polarity of microtubules?

Only the alpha-tubulin of a heterodimer can bind to the ring of gamma-subunits

With which of the following structures are intermediate filaments associated?

Option A: hemidesmosomes Option B: All of the choices are correct. Option C: the nuclear envelope in the center of the cell Option D: desmosomes Option E: the neurofilaments of neuron axons

View the video first, then answer the question. Traction forces shown in the fibroblast movement simulation in this video:

Option A: indicate that the forces being exerted are multipolar. Option B: both of the choices. Option C: None of the choices is correct. Option D: suggest the majority of the forces are being exerted at the leading edge of the cell.

A small zone of fluorescent microtubules in a cell is photobleached so that their fluorescent label gives off no light. Some time later fluorescence returns to the bleached zone in the cell. Which of the following is a possible explanation for the recovery of fluorescence in the region of the cell previously bleached?

Option A: movement of microtubules through the bleached zone Option B: the dynamics of the microtubules turning over in that bleached zone of the cell and the growth of new microtubules into the bleached zone Option C: All of the choices are correct. Option D: the growth of new microtubules into the bleached zone Option E: the dynamics of the microtubules turning over in that bleached zone of the cell

View the video first, then answer the question. 0:05 During the timeframe shown in this video:

Option A: the Xenopus embryo visibly develops at least two tissue types. Option B: development of the forebrain is seen in the upper right screen area. Option C: All of the choices are correct. Option D: development of the neural plate and neural tube are visible. Option E: None of the choices is correct.

Based on what is known about the involvement of calcium ions in exocytosis, what should happen if Ca2+ ions are injected into a cell?

Option D: Wholesale exocytosis of secretory product occurs.

How do misfolded proteins get to the cytoplasm to be destroyed?

Proteins are transported back to the cytosol through the translocon that brought them into the ER lumen or through a separate dislocation channel of uncertain identity.

Microtubule-associated proteins (MAPs) can serve which of the following functions?​

Providing stability to the microtubule by biding to the ends.

Which of the following is a difference between the coats of COPII- and clathrin-coated vesicles?

The outer scaffold subunits of the clathrin lattice of coated vesicles overlap extensively, while those of the COPII lattice of coated vesicles do not overlap.

You incubate liposomes with a series of purified proteins normally found in the coats of cell transport vesicles. After adding one of them to the liposome mixture, budding of vesicles from the liposomes began. What does this mean?

The protein is involved in the initiation of vesicle formation.

Phospholipids are made by integral ER membrane enzymes whose active sites face the cytosol and they are inserted into the outer (cytoplasmic) leaflet of the ER membrane. How then do lipids destined for the luminal leaflet of the ER membrane get there?

There are enzymes called flippases that flip these lipids later into the opposite leaflet.

Which of the following statements about microsomes is NOT TRUE?

They cannot be fractioned further.

When Rabs have bound to GTP, what do they do?

They recruit specific cytosolic tethering proteins to specific membrane surfaces.

What would happen to the movement of vesicles toward their eventual target if a microtubule inhibitor like colchicine were added to the cells?

Vesicle movement would slow or stop.

What happens to a newly synthesized glycoprotein after the binding of calnexin or calreticulin to help the protein correctly complete its folding?

When the glycoprotein's folding is correctly completed, the remaining glucose on its oligosaccharide chain is eventually removed enzymatically and the glycoprotein is released from the chaperone.

One of the WASP/WAVE family of proteins, specifically WASP, the founding member of the family, is associated with what disease below?

Wiskott-Aldrich syndrome

A structure is described as two cylindrical structures about 0.2 µm in diameter and about twice as long that contain nine evenly spaced blades, each of which consists of three microtubules. One of the three microtubules in each triplet is complete while the other two are incomplete. The nine complete microtubules are connected to a central hub with nine spokes called the cartwheel. What is this structure called?

a centriole

Which organism below lacks both centrosomes and centrioles?

a palm tree

Which property below is most characteristic of intermediate filaments?

ability to absorb mechanical stresses applied by the extracellular environment

The focal complexes that form near the leading edge of a motile cell exert traction force through their associated __________ and then typically disassemble as the cell moves forward or mature into larger, more contractile focal adhesions.

actin filaments

Which of the following could be a method used to label microtubules with a fluorescent dye?

attaching a fluorescently-labeled antibody to tubulin and inducing a cell to express the gene for tubulin that has been fused to the gene for GFP

Fluorescence microscopy allows investigators to view things _________ of regular light microscopes.

below the limits of resolution

What is thought to shield lysosomal membranes against attack by their enclosed enzymes?

carbohydrate chains attached to integral membrane proteins

Substances that enter the cell by receptor-mediated endocytosis bind receptors that collect in specialized domains of the plasma membrane called ______.

coated pits

What drives the engulfment of particulate material by phagocytosis?

contractile activities of the actin-containing microfilaments that underlie the plasma membrane

In receptor down-regulation, signaling receptors are _____________________

covalently attached to ubiquitin subjected to endocytosis internalized and destroyed

Each protofilament is assembled from _________ building blocks.

dimeric

Which of the following words best describes the structure of an actin filament?

double helix

Which molecule below is a GTP-binding protein that is required for the release of a clathrin-coated vesicle from the membrane on which it was formed?

dynamin

Which endosomes are typically located near the peripheral region of the cell?

early endosomes

Asymmetry of cellular membranes is established initially in the _____________.

endoplasmic reticulum

Fusion of a secretory vesicle with the plasma membrane and discharge of its contents is called ___________.

exocytosis

The process of membrane fusion and subsequent content discharge is called ______ and is usually triggered by a release of ______.

exocytosis, Ca2+ ions

In a pulse-chase procedure, if the chase is longer, which statement below correctly describes the location of the radioactively labeled proteins in the cell?

farther from the synthesis site

Which type of actin-binding protein is known to decrease cytoplasmic viscosity by breaking existing actin filaments into two or more pieces?

filament-severing proteins

What leads to the degradation of the contents of late endosomes by lysosomal enzymes?

fusion of late endosomes containing intraluminal vesicles with a lysosome

The tip, or __________, of an elongating axon resembles a highly motile, crawling fibroblast, unlike the bulk of the axon that shows little outward evidence of motile activity.

growth cone

Which of the following treatments disassembles microtubules in living cells?

hydrostatic pressure

If you were to fix a fish keratocyte and stain it with fluorescent antibodies for myosin II, where would you see the myosin II?

in a band where the rear of the lamellipodium joins the rest of the cell

In what form are proteins and neurotransmitters usually transported down the axon of a nerve cell?

inside transport vesicles

What determines the specificity of vesicle fusion to a target membrane?

interactions between specific combinations of interacting proteins, including tethering proteins, Rabs and SNAREs assembled at that site in the cell

Which element of the cytoskeleton is found in the cytoplasm and the nucleus?

intermediate filaments

Which type of cytoskeletal element is described as tough, ropelike fibers composed of a variety of related proteins like keratin?

intermediate filaments

Netrin ________.

is a diffusible factor that acts as an attractant for axons growing within the early embryo

Which protein below is often a component of intermediate filaments?

keratin

Which of the following molecular motors is known to travel in an anterograde direction along microtubules?

kinesins

View the video first, then answer the question. In the four videos showing moving cells:

lamellipodia are evident at the leading edge as the cells move forward.

Which of the following developmental processes would be inhibited by colchicine?

longation of the cells of the neural plate leading to its thickening

In general, diseases that result from a deficiency of a single lysosomal enzyme are called ________.

lysosomal dissociation disorders

What sugar is usually removed from the N-linked core oligosaccharide chains on proteins in the Golgi complex as opposed to the glucose residues trimmed off in the ER?

mannose

Along which structure do membranous vesicles and organelles typically engage in local movement in the cell periphery of an animal cell?

microfilaments

The endomembrane system when homogenized is broken up into vesicles, which are heterogeneous but similar in size. These vesicles can be purified and, after purification, often retain their biological activity. They are collectively referred to as _________.

microsomes

Along which structure do membranous vesicles and organelles typically move long distances in an animal cell?

microtubules

What is thought to direct the movement of vesicles through the cytoplasm to their final destination?

microtubules

Dyneins generally move toward the __________ of the microtubule to which they are bound.

minus end

A shift in the concentration or activity of which type of proteins can cause a shift in the equilibrium between actin monomers and polymers?

monomer-sequestering proteins

How is movement of vesicular-tubular carriers directed from the ERGIC to the Golgi complex?

movement occurs on microtubule tracks

Late endosomes are also referred to as _______.

multivesicular bodies and MVBs

The amorphous, electron-dense material that surrounds the two barrel-shaped centrioles and is part of the centrosome is called ___________.

pericentriolar material (PCM)

The uptake of relatively large particulate matter into the cell is called _________.

phagocytosis

The vesicle containing material taken into the cell by phagocytosis is called a(n) _________.

phagosome

What seems to control the assembly and disassembly of intermediate filaments?

phosphorylation and dephosphorylation

The cross-bridges that hold intermediate filaments together are composed of _______.

plectin

What is responsible for degrading misfolded proteins in the cytoplasm?

proteasomes

The Binding Immunoglobulin Protein (BiP) is a molecular chaperone that is essential for the translocation of secreted peptides into the lumen of the ER. Because it is a chaperone, it is important for _________________________.

protein folding

Typically, receptors for hormones or growth factors are destroyed during endocytosis, leading to a reduction in the cell's sensitivity to further stimulation by that particular hormone or growth factor. This is a mechanism by which cells regulate their ability to respond to extracellular messengers. What is it called?

receptor down-regulation

Which of the following nonmuscle cell activities do not involve actin filaments often working in concert with myosin motors?

red blood cells carrying oxygen

The movement of endocytic vesicles formed in the neuron terminals from the synapse to the cell body is said to be in a(n) ________ direction.

retrograde

Which of the following is NOT an activity for which cell locomotion is important?

secretion of digestive juices

What appears to be an early step in the process of vesicle fusion to its target compartment?

tethering of vesicles to the target compartment by extended, fibrous proteins

what binds to the signal of a receptor and the clathrin coat helping the receptor to be trapped in coated pits prior to endocytosis?

the AP2 adaptor

The signal sequence is typically found on _________ of a peptide designated to be inserted into the lumen of the rough endoplasmic reticulum (RER).

the amino-terminus

Which of the models below suggests that the Golgi cisternae are transient structures that form at the cis face of the stack by fusion of membranous carriers from the ER and ERGIC and that each cisterna travels through the Golgi complex from the cis to the trans end of the stack, changing in composition as it progresses?

the cisternal maturation model

Which of the following developmental processes would be inhibited by cytochalasin?

the curving of the neural plate to form the neural tube

What molecules do the AP2 adaptors of the clathrin coat connect?

the cytoplasmic tails of specific membrane receptors and clathrin molecules

View the video first, then answer the question. Physical manipulation of a cultured cell shows:

the deformation forces shown are unable to change the width of the lamellipodium

To which end of microtubules are tubulin subunits primarily added in vitro?

the plus end

What determines the sequence of sugar addition to glycoproteins traveling through the Golgi complex?

the spatial arrangement of specific glycosyltransferases that contact proteins as they pass through the Golgi complex

Which of the following is triggered by the accumulation of misfolded proteins in the ER?

the unfolded protein response

Which model of Golgi complex formation suggests that the cisternae of a Golgi stack remain in place as stable compartments held together by a protein scaffold, while the cargo is shuttled through the Golgi via vesicles that bud from one compartment and fuse with a neighboring one?

the vesicular transport model

The ____________ functions as a major sorting station, directing proteins to various destinations.

trans Golgi network

Microtubules are composed of two different types of ____________ subunit that form a _______________.​

tubulin; heterodimer

Motor proteins are able to generate force by ___________.

undergoing a series of conformational changes

What are the two functional categories of SNAREs?

v-SNAREs and t-SNAREs

How do Rabs appear to associate with membranes?

via a lipid anchor