Cell Bio - Chapter 17

Which of the following statements about the cytoskeleton is FALSE?

Covalent bonds between protein monomers hold together cytoskeletal filaments.

Which of the following statements about the cytoskeleton is TRUE?

Actin filaments are most highly concentrated in the cell cortex, whereas microtubules traverse the cytosol.

Which of the following below about intermediate filaments is FALSE?

Each filament is about 25 nm in diameter.

All intermediate filaments are of similar diameter because...

the central rod domains are similar in size and amino acid sequence.

Intermediate filaments help protect animal cells from mechanical stress because filaments...

in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells.

Which of the following is NOT a property exhibited by keratins, neurofilaments, and vimentins?

Phosphorylation causes disassembly during every mitotic cycle.

Which of the following about microtubules is FALSE?

a-Tublin and b-Tublin are covalently bound to make the tubulin dimer that then assembles into protofilaments.

Which about centrosome is FALSE?

Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.

Which about microtubules is TRUE?

Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.

The hydrolysis of GTP to GDP carried out by tubulin molecules...

allows the behavior of microtubules called dynamic instability.

The microtubules in a cell form a structural framework that can have all of the functions EXCEPT...

strengthening the cell's plasma membrane.

You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ....

binds to GTP-bound tubulin on microtublues.

Which about dynamic instability is FALSE?

The newly freed tubulin dimers from a shrinking microtuble can be captured immediately by growing microtubules and added to their plus ends.

Which situation will enhance microtubule shrinkage?

Addition of a drug that inhibits GTP exchange on free tubulin dimers.

Which about organellar movement in the cell is FALSE?

Only the microtubule cytoskeleton is involved in organellar movement.

Kinesins and dyneins...

often move in opposite directions.

Which about the movement of materials in a nerve axon is TRUE?

Microtubules within an axon are arranged such that all microtubules point in the same direction with their minus ends toward the nerve cell body.

Which component is NOT important for ciliary movement?

Sarcoplasmic reticulum.

Which about actin is FALSE?

The dynamic instability of actin filaments is important for cell movement.

Which applies to actin filaments or microtubules, but not both?

Depolymerization initiates at the plus ends.

For both actin and microtubule polymerization, nucleotide hydrolysis is important for...

decreasing the binding strength between subunits on filaments.

What do you predict to happen if actin monomers that bind on a nonhydronyzable form of ATP were incorporated into actin filaments?

Actin filaments would grow longer.

Actin mediated movement involves the coordination of many events in the cell. Which is not required for cell crawling?

Release of Ca2+ from the sarcoplasmic reticulum.

Which of the following is unlikely to be directly involved in the pathway that lamellipodia affects?

Myosin

Which structure shortens during muscle contraction?

Sacromeres.

Which of the following conditions would decrease the likelihood of skeletal muscle contraction?

Addition of a drug that blocks Ca2+ binding to troponin.

Which about skeletal muscle contraction is false?

The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction.

How many binding sites for a-tubulin does the ring complex possess?

13

Which of the following discoveries was made using fluorescence microscopy to observe the movement of kinesin molecules labeled with fluorescent marker proteins?

Kinesin molecules move preocessively along microtubules in 8-nm steps.

Which of the following best describes the function of the microtubule-associated protein augmin?

Promotes microtubule branching.

If the filaments in your micrograph really are actin filaments, how thick are they?

About the same thickness as the plasma membrane.

Which of the following about skeletal muscle is TRUE?

The cells possess multiple nuclei.