Cell Bio Exam 2

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

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

4.5

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

AP2 adaptor

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

ARF-1 (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

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

Which coated vesicles move materials in a retrograde direction from the ERGIC and Golgi back to the ER?

COPI coated vesicles

What is NOT an actin-binding protein?

Calmodulin

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?

Could be: movement of microtubules through bleached zone, growth of new microtubules into the bleached zone, dynamics of the microtubules turning over in that bleached zone of the cell and the growth of new microtubules into bleached zone, the dynamics of the microtubules turning over in the bleached zone

You inject labelled 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.

Where does glycosylation take place?

Golgi and RER

What are differences between early and late endosomes?

In late endosomes, the outer boundary membrane has budded inward on its lumenal surface creating a group of vesicles Late endosomes exhibit a lower pH than early ones Late endosomes have a pop. of vesicles crowding their interior Early endosomes exchange Rab5 proteins for Rab7 proteins as they transform into late endosomes.

What happens to 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

What kind of organisms lack centrosomes and centrioles?

Plants

BiP is a molecular chaperone that is essential for the translocation of secreted peptides into lumen of ER. Bc/ it is a chaperone, it is important for ______

Protein folding

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 seperate dislocation channel of uncertain identity

Macrotubule-associated proteins (MAPs) can do what?

Provide stability to microtubule by binding to the ends

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

What is the main difference between the coats of COPII and clathrin coated vesicles?

The outer scaffold subunits of clathrin lattice of coated vesicles overlap extensively, while those of the COPII laticce 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

Which statement about microsomes is FALSE?

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 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 oligosaccharide chain is evetually removed enzymatically and the glycoprotein is released from the chaperone.

The protein WASP is associated with what disease?

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

What property 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

The signal sequence is typically found on _____ of a peptide designated to be inserted into the lumen of the RER.

amino-terminus

What could be a methof 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

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

clathrin molecules, and cargo molecules

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 phagocytosis?

contractile activities of the actin-containing microtubules that underlie the mitochondrial membrane

In receptor down-regulation, signalling receptors are ________

covalently attached to ubiquitin, subjected to endocytosis, and internalized and destroyed.

Which chemical below is known to block the plus ends of actin filaments while allowing depolymerization at the minus ends?

cytochalasin

What kinds of structures are intermediate filaments associated?

desmosomes, hemidesmosomes, the neurofilaments of neuron axons, the nuclear envelope in the center of the cell

Each protofilament is assembled from _______ building blocks

dimeric

What kind of structure does an actin filament have?

double helix

Which molecule 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

What is an example of a developmental process that would be inhibited by colchisine?

elongation of cells of the neural plate, leading to its thickening

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, calcium 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

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?

flippases flip them to the opposite leaflet

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

What treatment disassembles microtubules in a living cell?

hydrostatic pressure

Where would you see 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 specificity of vesicle fusion to a target membrane?

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

What appears to be the most extensible?

intermediate filaments

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 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

In general, diseases that result from a deficiency of a single lysosomal enzymer are called ______.

lysosomal storage 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

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

microtubule tracks

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

microtubules

what directs the movement of vesicles through the cytoplasm to final destination?

microtubules

Dyneins generally move toward the ________ end of the microtubule

minus

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

monomer-sequestering proteins

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 large particulates into cell is called:

phagocytosis

The vesicle containing material taken into cell by phagocytosis is called a

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

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

plus end

In S1-decorated microfilaments, the barbed end is the __________ and the pointed end is the ___________

plus end/fast growing tip; minus end/slow growing tip

What are functions performed by the cytoskeleton?

positions various organelles within the cell interior, provides structural support that determines cell shape and resists deforming forces, serves as a force-generating apparatus that moves cells from one place to another provides a network of tracks over which materials like mRNA and organelles move within cells.

What is responsible for degrading misfolded proteins in the cytoplasm?

proteasomes

What nonmuscle cell activity DOES NOT involve actin filaments working 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 _________ direction

retrograde

What 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 target compartment by extended, fibrous proteins

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 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

What is triggered by accumulation of misfolded proteins in 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

Individual monomers of a microfilament move down the length of the microfilament from the plus end to the minus end in vitro in a process known as:

treadmilling

Microtubules are composed of 2 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- and t-

What happens to movement of vesicles if microtubule inhibitor like colchicine was added to cells?

vesicle movement would slow or stop.

How do Rabs appear to associate with membranes?

via a lipid anchor

What would happen if calcium ions are injected into a cell?

wholesale exocytosis of secretory product