Exam 3 Flashcards
The cytoskeletal system characterized as being comprised of rope-like fibers that give the cell mechanical strength and distribute mechanical stress are:
a. intermediate filaments
b. myosin thick filament
c. actin filaments
d. microtubules
a. intermediate filaments
Which of the following represents the placement of microtubules in an epithelial cell?
A. none of these
B. C
C. A
D. B
D. B
(Q001) Which of the following statements about the cytoskeleton is FALSE?
a. Covalent bonds between protein monomers hold together cytoskeletal filaments.
b. The cytoskeleton is made up of three types of protein filaments.
c. The cytoskeleton of a cell can change in response to the environment.
d. The cytoskeleton controls the location of organelles in eukaryotic cells.
a. Covalent bonds between protein monomers hold together cytoskeletal filaments.
(Q027) For both actin and microtubule polymerization, nucleotide hydrolysis is important for
a. increasing the rate at which subunits are added to the filaments.
b. promoting nucleation of filaments.
c. stabilizing the filaments once they are formed.
d. decreasing the binding strength between subunits on filaments.
d. decreasing the binding strength between subunits on filaments.
(Q010) Which of the following statements about the structure of microtubules is FALSE?
a. The two ends of a protofilament are chemically distinct, with α-tubulin exposed at one end and β-tubulin exposed at the other end.
b. α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.
c. Microtubules are built from protofilaments that come together to make a hollow structure.
d. Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity.
b. α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.
(Q013) The hydrolysis of GTP to GDP carried out by tubulin molecules
a. occurs because the pool of free GDP has run out.
b. provides the energy needed for tubulin to polymerize.
c. tips the balance in favor of microtubule assembly.
d. allows the behavior of microtubules called dynamic instability.
d. allows the behavior of microtubules called dynamic instability.
(Q012) Which of the following statements about microtubules is TRUE?
a. The centromere nucleates the microtubules of the mitotic spindle.
b. ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.
c. Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.
d. Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell.
c. Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.
(Q025) Which of the following statements about actin is FALSE?
a. Actin filaments are nucleated at the side of existing actin filaments in lamellipodia.
b. ATP hydrolysis decreases actin filament stability.
c. Linkage of actin to the desmosome provides structural integrity to the tissue.
d. Actin at the cell cortex helps govern the shape of the plasma membrane.
c. Linkage of actin to the desmosome provides structural integrity to the tissue.
(Q036) Which of the following statements about skeletal muscle contraction is FALSE?
a. When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane.
b. During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.
c. A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament.
d. 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 Ca into the sarcoplasmic reticulum, triggering a muscle contraction.
d. 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 Ca into the sarcoplasmic reticulum, triggering a muscle contraction.
(Q034) Which of the following structures shorten during muscle contraction?
a. myosin filaments
b. flagella
c. actin filaments
d. sarcomeres
d. sarcomeres
(Q008) You are studying nuclear lamins and use recombinant DNA technology to alter the coding sequence of a nuclear lamin gene. The alteration you make creates a situation such that the gene now codes for a nuclear lamin protein that can no longer be phosphorylated when the nuclear envelope is broken down during mitosis. What do you predict would happen if the cell only had the altered nuclear lamin gene (and not the unaltered version)?
a. Disassembly of the nuclear lamins will occur prematurely because the lamins cannot be phosphorylated.
b. Nuclear lamins will be unable to produce dimers, as the coiled-coil formation will be disrupted.
c. Nuclear lamins will no longer disassemble properly during mitosis.
d. Mitosis should proceed as usual because the dephosphorylation of the lamin is what is important for nuclear lamina assembly during mitosis, so phosphorylation will not be necessary.
c. Nuclear lamins will no longer disassemble properly during mitosis.
(Q011) Which of the following statements about the function of the centrosome is FALSE?
a. Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules.
b. Centrosomes are the major microtubule-organizing center in animal cells.
c. Centrosomes contain hundreds of copies of the gamma-tubulin ring complex important for microtubule nucleation.
d. 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.
d. 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.
What must happen at the end of the microtubule in order for it to stop shrinking and start growing again?
a. Interaction with ARP in order to seed a branch point
b. Once a microtubule starts shrinking, it must completely disassemble before a new microtubule can start growing again.
c. Phosphorylation of tau protein so it will bind and stabilize the microtubule
d. Addition of a sufficient number of GTP-loaded tubulin subunits to the growing end to quickly cover up the GDP-containing subunits
d. Addition of a sufficient number of GTP-loaded tubulin subunits to the growing end to quickly cover up the GDP-containing subunits
Question 14: Shown below is the structure of a bipolar mitotic spindle. Which element(s) is/are the astral microtubules?
a. none of these
b. B
c. A
d. C
c. A
What is tensegrity?
a. A structural principle based on a system of isolated components under compression inside a network of continuous tension.
b. The stabilizing of a microtubule network due to end-binding proteins inhibiting disassembly.
c. The homeostasis that a cell achieves when it has the correct complement of transporters and channels.
d. The state of “rigor” that occurs in a muscle after death.
a. A structural principle based on a system of isolated components under compression inside a network of continuous tension.
(Q005) Which of the following statements about the cell cycle is FALSE?
a. An unfavorable environment can cause cells to arrest in G1.
b. A cell has more DNA during G2 than it did in G1.
c. The cleavage divisions that occur in an early embryo have short G1 and G2 phases.
d. Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.
d. Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.
(Q007) Progression through the cell cycle requires a cyclin to bind to a Cdk because
a. without cyclin binding, a cell-cycle checkpoint will be activated.
b. cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle.
c. the cyclins are the molecules with the enzymatic activity in the complex.
d. the binding of a cyclin to Cdk is required for Cdk enzymatic activity.
d. the binding of a cyclin to Cdk is required for Cdk enzymatic activity.
(Q032) Which of the following statements about kinetochores is TRUE?
a. Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome.
b. Kinetochores assemble on chromosomes that lack centromeres.
c. Kinetochores assemble onto chromosomes during late prophase.
d. Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules.
c. Kinetochores assemble onto chromosomes during late prophase.
(Q043) Apoptosis differs from necrosis in that necrosis
a. causes cells to swell and burst, whereas apoptotic cells shrink and condense.
b. involves a caspase cascade.
c. causes DNA to fragment.
d. requires the reception of an extracellular signal.
a. causes cells to swell and burst, whereas apoptotic cells shrink and condense.
(Q029) Which word or phrase below best describes the phase in mitosis depicted in Figure 18-29?
a. prometaphase
b. S-phase checkpoint
c. metaphase
d. anaphase
c. metaphase
(Q006) Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2?
a. The cell would be unable to enter G .2
b. The cell would enter M phase under conditions when normal cells would not.
c. The cell would be unable to enter M phase.
d. The cell would pass through M phase more slowly than normal cells.
b. The cell would enter M phase under conditions when normal cells would not.
(Q003) Which of the following events does NOT usually occur during interphase?
a. The centrosomes are duplicated.
b. DNA is replicated.
c. Cells grow in size.
d. The nuclear envelope breaks down.
d. The nuclear envelope breaks down.
(Q034) Which of the following statements about the anaphase-promoting complex (APC) is FALSE?
a. It inhibits M-Cdk activity.
b. M-Cdk stimulates its activity.
c. It is continuously active throughout the cell cycle.
d. It promotes the degradation of proteins that regulate M phase.
c. It is continuously active throughout the cell cycle.
(Q042) Programmed cell death occurs
a. by means of an intracellular suicide program.
b. only in unhealthy or abnormal cells.
c. rarely and selectively only during animal development.
d. only during embryonic development.
a. by means of an intracellular suicide program.
(Q017) The G1 DNA damage checkpoint
a. causes cells to proceed through S phase more quickly.
b. is activated by errors caused during DNA replication.
c. involves the inhibition of cyclin–Cdk complexes by p21.
d. activates APC.
c. involves the inhibition of cyclin–Cdk complexes by p21.
Which of the following changes takes place when a skeletal muscle contracts?
a. Myosin filaments contract.
b. Actin filaments contract.
c. Sarcomeres become shorter.
d. Z discs move further apart.
c. Sarcomeres become shorter.
How are spindle microtubules attached to chromosomes?
a. The plus ends of the microtubule bind directly to DNA
b. The microtubules bind to the kinetochore complexes through a connecting protein
c. The microtubules bind to cohesin complexes on the DNA
d. The minus ends of the microtubules bind directly to a protein complex on DNA
b. The microtubules bind to the kinetochore complexes through a connecting protein
The expression levels of different __________ fluctuate throughout the cell cycle.
a. cyclins
b. Cdks
c. cyclins and Cdks
d. phosphates
a. cyclins
What determines the position of the cleavage furrow of the dividing cell?
a. The interpolar microtubules send signals to form a cleavage furrow between the poles.
b. The two spindle poles send signals to the plasma membrane so that the cleavage furrow forms in the same plane as the two poles.
c. Astral microtubules contact the membrane and activate proteins to form a central furrow.
d. The cleavage furrow position is determined randomly.
a. The interpolar microtubules send signals to form a cleavage furrow between the poles.
In which phase of mitosis does the nuclear envelope break down?
a. telophase
b. metaphase
c. prometaphase
d. anaphase
c. prometaphase
Consider the events that lead to the formation of the new nucleus at telophase. How do nuclear and cytosolic proteins become properly re-sorted so that the new nucleus contains nuclear proteins but not cytosolic proteins?
a. Because the nuclear envelope reassembles on the surface of the chromosomes, cytosolic proteins are excluded from the reforming nucleus. Nuclear proteins are selectively imported through the NPC by nuclear transport receptors that recognize the NLS they contain..
b. Nuclear proteins bind chromosomes during mitosis. Because the nuclear envelope
reassembles on the surface of the chromosomes, nuclear proteins end up inside the nucleus and cytoplasmic proteins end up on the outside of the nuclear envelope.
c. Proteins are degraded during mitosis, so cytoplasmic and nuclear proteins are targeted via their normal targeting mechanisms.
d. Cytosolic proteins are excluded from the reforming nucleus due to their cytoplasmic signal recognition sequence. Nuclear proteins are selectively imported through the NPC due to their nuclear localization sequence..
a. Because the nuclear envelope reassembles on the surface of the chromosomes, cytosolic proteins are excluded from the reforming nucleus. Nuclear proteins are selectively imported through the NPC by nuclear transport receptors that recognize the NLS they contain..
All of the following is true EXCEPT:
a. Apoptosis is mediated by special intracellular proteases, one of which cleaves nuclear lamins.
b. Cells do not pass directly from G1 to M unless there are sufficient nutrients to complete an entire cell cycle.
c. The enzymatic activity of a Cdk protein is determined both by the presence of a bound cyclin and by the phosphorylation state of the Cdk.
d. Developing neurons compete for limited amounts of survival factors.
b. Cells do not pass directly from G1 to M unless there are sufficient nutrients to complete an entire cell cycle.
Which of the following is TRUE regarding the role of Ca2+ in muscle contraction?
a. Ca2+ binds troponin, causing it to move tropomyosin and thereby expose actin filaments to myosin heads.
b. Ca2+ release is required for the refractory stage that returns the muscle to its pre-contraction state.
c. Ca2+ binding to myosin causes it to release from actin.
d. Ca2+ binding is required to maintain the structure of the actin filament.
a. Ca2+ binds troponin, causing it to move tropomyosin and thereby expose actin filaments to myosin heads.
What is the function of condensins?
a. to shorten the contractile ring
b. to break down the nuclear envelope
c. to coil sister chromatids into a compact form
d. to hold sister chromatids together
c. to coil sister chromatids into a compact form
In the graph below, Peak B would be expected to contain cells that are in which phase(s) of the cell cycle?
a. prophase
b. G1
c. G2 and prophase
d. G2
c. G2 and prophase
In the EM images below, which cell(s) are undergoing apoptosis?
a. Only A
b. Only B
c. B and C
d. Only C
c. B and C
The slow rise of S cyclin levels throughout G1 phase is due to ________, and the abrupt decrease is caused by __________.
a. synthesis; mitosis
b. phosphorylation; translation
c. transcription; proteolysis
d. import; export
c. transcription; proteolysis
What is a reasonable explanation for why cells have evolved a special G0 phase to exit from the cell cycle, rather than just stopping in G1 and not moving on to S phase?
a. Because it takes too much energy to keep synthesizing G1 cyclins when they are not
needed.
b. Because the G1 state leaves the cell in a vulnerable state since it has not yet duplicated its genome and thus is more sensitive to radiation damage.
c. The G0 state offers protection from aberrant activation of cell division because the cell-cycle control system is largely dismantled.
d. Because the G0 state is more stable since the dynamic instability of microtubules is paused since spindles are not needed anymore.
c. The G0 state offers protection from aberrant activation of cell division because the cell-cycle control system is largely dismantled.
Where is Ca2+ stored inside a muscle cell?
a. Golgi apparatus
b. mitochondria
c. sarcoplasmic reticulum
d. neurosecretory vesicles
c. sarcoplasmic reticulum
Cyclins are targeted for destruction in a cell-cycle-dependent manner by:
a. ubiquitination
b. phagocytosis
c. phosphorylation
d. G-protein binding
a. ubiquitination
PDGF is encoded by a gene that can cause cancer when expressed inappropriately. Why do cancers not arise at wounds in which PDGF is released from platelets?
A. PDGF is only released during normal blood clotting and not at wounds.
B. PDGF has no association with cancer development.
C. The limited release of PDGF at a wound site triggers cell division of neighboring cells for a limited amount of time, until the PDGF is degraded.
D. Wounds are naturally resistant to the oncogenic effects of PDGF.
C. The limited release of PDGF at a wound site triggers cell division of neighboring cells for a limited amount of time, until the PDGF is degraded.
Which of the following types of cells would you expect to contain a high density of intermediate filaments in their cytoplasm? (Can pick multiple)
A. Amoeba proteus (a free-living amoeba)
B. Skin epithelial cell
C. Smooth muscle cell in the digestive tract
D. Escherichia coli
E. Nerve cell in the spinal cord
F. Sperm cell
G. Plant cell
B. Skin epithelial cell
C. Smooth muscle cell in the digestive tract
E. Nerve cell in the spinal cord