GCD 3033 final practice problems
Which of the following statements about the cytoskeleton is TRUE?
Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.
Compared to the normal situation, in which actin monomers carry ATP, what do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments?
Actin filaments would grow longer.
Which of the following statements about apoptosis is TRUE?
Apoptosis can be promoted by the release of cytochrome c into the cytosol from mitochondria.
The figure below shows how the movement of dynein causes the flagellum to bend. If instead of the normal situation, the polarity of the adjacent doublet of microtubules were to be reversed (see B), what do you predict would happen?
Bending would occur, except that the right microtubule doublet would move down relative to the left one.
The figure below shows the leading edge of a lamellipodium. Which of the following statements is FALSE?
Capping proteins bind to the minus end of actin filaments.
You are examining a cell line in which activation of the Rho family member Rac promotes lamellipodia formation. Which of the following statements is most likely to be TRUE?
Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells.
You create cells with a version of the origin recognition complex, ORC, that cannot be phosphorylated by S-Cdk and thus cannot be inactivated. Which of the following statements describes the likely consequence of this change in ORC?
Cells will replicate some regions of the genome more than once in a cell cycle.
Which of the following statements is TRUE?
Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.
The length of time a G protein will signal is determined by the
GTPase activity of Gα.
Which organelle fragments during mitosis?
Golgi apparatus
Which of the following statements is TRUE?
In anaphase B, microtubules associated with the cell cortex shorten.
How does S-Cdk help guarantee that replication occurs only once during each cell cycle?
It phosphorylates and inactivates Cdc6
Which of the following statements about kinetochores is TRUE?
Kinetochores assemble onto chromosomes during late prophase.
anaphase-promoting complex (APC)
M-Cdk stimulates its activity. It promotes the degradation of proteins that regulate M phase. It inhibits M-Cdk activity
Which of the following statements 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 of the following statements about microtubules is TRUE?
Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.
When the cytosolic tail of the __________ receptor is cleaved, it migrates to the nucleus and affects gene regulation.
Notch
Which of the following statements about the cell cycle is FALSE?
Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.
Which of the following statements is TRUE?
PI 3-kinase phosphorylates a lipid in the plasma membrane.
Which of the following statements about animal connective tissues is TRUE?
Proteoglycans can resist compression in the extracellular matrix.
The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000 -dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be TRUE?
QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.
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?
The cell would enter M phase under conditions when normal cells would not.
What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only?
The cells produced would get smaller and smaller.
When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is TRUE?
The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras.
Which of the following statements about actin is FALSE?
The dynamic instability of actin filaments is important for cell movement.
Which of the following statements about plant cell walls is TRUE?
The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall.
Which of the following statements is TRUE?
The mitotic spindle helps segregate the chromosomes to the two daughter cells.
Which of the following events does NOT usually occur during interphase? Cells grow in size. The centrosomes are duplicated. DNA is replicated. The nuclear envelope breaks down
The nuclear envelope breaks down
Which of the following statements is TRUE?
The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.
The following happens when a G-protein-coupled receptor activates a G protein.
The α subunit exchanges its bound GDP for GTP.
The figure below shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine?
a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP
Which of the following types of mutation would be expected to promote uncontrolled cell proliferation?
a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor
Which of the following types of alteration would be most likely to prevent receptor dimerization?
a mutation that prevents RGFR from binding to RGF
Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction?
addition of a drug that blocks Ca²⁺ binding to troponin
Which of the situations below will enhance microtubule shrinkage?
addition of a drug that inhibits GTP exchange on free tubulin dimers
Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in the figure below. Which of the following would enhance this effect of the acetylcholine?
addition of a high concentration of a nonhydrolyzable analog of GTP
Which type of junction involves a connection to the actin cytoskeleton?
adherens junctions
Proteoglycans in the extracellular matrix of animal tissues
allow cartilage to resist compression.
The hydrolysis of GTP to GDP carried out by tubulin molecules
allows the behavior of microtubules called dynamic instability.
A major distinction between the connective tissues in an animal and other main tissue types such as epithelium, nervous tissue, or muscle is the
amount of extracellular matrix in connective tissues
Tight junctions
are formed from claudins and occludins.
Condensins
assemble into complexes on the DNA when phosphorylated by M-Cdk.
Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells?
assembly of the contractile ring
In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated?
at the end of G2
Hemidesmosomes are important for
attaching epithelial cells to the extracellular matrix.
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 that MtA
binds to GTP-bound tubulin on microtubules.
Programmed cell death occurs
by means of an intracellular suicide program
Induced pluripotent stem (iPS) cells
can be created by the expression of a set of key genes in most somatic cell types, including cells derived from adult tissues.
Adherens junctions
can be used to bend epithelial sheets into tubes.
A pluripotent cell
can give rise to most of the tissues and cell types in the body.
Cells that are terminally differentiated
can no longer undergo cell division.
An adult hemopoietic stem cell found in the bone marrow
can undergo self-renewing divisions for the lifetime of a healthy animal.
Apoptosis differs from necrosis in that necrosis
causes cells to swell and burst, whereas apoptotic cells shrink and condense.
The principal microtubule-organizing center in animal cells is the
centrosome.
At the end of DNA replication, the sister chromatids are held together by the
cohesins
Which of the following molecules is NOT found in plants?
collagen
Mouse embryonic stem (ES) cells
come from the inner cell mass of early embryos.
During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in __________ signaling.
contact-dependent
The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to
create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane.
Levels of Cdk activity change during the cell cycle, in part because
cyclin levels change during the cycle.
For both actin and microtubule polymerization, nucleotide hydrolysis is important for
decreasing the binding strength between subunits on filaments.
Which of the following mechanisms is NOT directly involved in inactivating an activated RTK? dephosphorylation by protein tyrosine phosphatases dephosphorylation by serine/threonine phosphatases removal of the RTK from the plasma membrane by endocytosis digestion of the RTK in lysosomes
dephosphorylation by serine/threonine phosphatases
The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by
diffusing into cells and stimulating the cyclase directly
A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to
disassemble its nuclear lamina at prometaphase.
A cell that is terminally differentiated will
dismantle the cell-cycle control system.
Cells in the G0 state
do not divide.
Mitogens are
extracellular signals that stimulate cell division.
The concentration of mitotic cyclin (M cyclin)
falls toward the end of M phase as a result of ubiquitylation and degradation.
The plasmodesmata in plants are functionally most similar to which animal cell junction?
gap junction
Which of the following does not occur during M phase in animal cells?
growth of the cell
When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a
hormone.
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.
The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by
inhibiting cyclin transcription.
A cell can crawl through a tissue because of the transmembrane __________ proteins that can bind to fibronectin outside of the cell.
integrin
All members of the nuclear receptor family
interact with signal molecules that diffuse through the plasma membrane.
Foreign substances like nicotine, morphine, and menthol exert their initial effects by
interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus.
At desmosomes, cadherin molecules are connected to
intermediate filaments.
The G1 DNA damage checkpoint
involves the inhibition of cyclin-Cdk complexes by p21
A basal lamina
is a thin layer of extracellular matrix underlying an epithelium.
A protein kinase can act as an integrating device in signaling if it
is activated by two or more proteins in different signaling pathways.
A malignant tumor is more dangerous than a benign tumor because
its cells invade other tissues.
Cadherins
mediate cell-cell attachments through homophilic interactions.
Disassembly of the nuclear envelope
must occur for kinetochore microtubules to form in animal cells.
Your friend works in a biotech company that has just discovered a drug that seems to promote lamellipodia formation in cells. Which of the following molecules is unlikely to be directly involved in the pathway that this drug affects?
myosin
Kinesins and dyneins
often move in opposite directions to each other.
Plasmodesmata
permit small molecules to pass from one cell to another.
When a terminally differentiated cell in an adult body dies, it can typically be replaced in the body by a stock of
proliferating precursor cells.
Fibroblasts organize the collagen of the extracellular matrix by
pulling the collagen into sheets or cables after it has been secreted.
Cell movement involves the coordination of many events in the cell. Which of the following phenomena is not required for cell motility?
release of Ca²⁺ from the sarcoplasmic reticulum
Cytokinesis in animal cells
requires ATP.
Which of the following structures shorten during muscle contraction?
sarcomeres
Which of the following items is not important for flagellar movement?
sarcoplasmic reticulum
Sister chromatid separation occurs because __________ are destroyed by the APC/C.
securins
The microtubules in a cell form a structural framework that can have all the following functions except which one?
strengthening the plasma membrane
Progression through the cell cycle requires a cyclin to bind to a Cdk because
the binding of a cyclin to Cdk is required for Cdk enzymatic activity.
All intermediate filaments are of similar diameter because
the central rod domains are similar in size and amino acid sequence.
A friend declares that chromosomes are held at the metaphase plate by microtubules that push on each chromosome from opposite sides. Which of the following observations does not support your belief that the microtubules are pulling on the chromosomes?
the jiggling movement of chromosomes at the metaphase plate
Which type of junction contributes the most to the polarization of epithelial cells?
tight junctions
Both multicellular plants and animals have
tissues composed of multiple different cell types.
The artificial introduction of three key __________ into an adult cell can convert the adult cell into a cell with the properties of ES cells.
transcription factors
