BCMB Exam 5

D

A cell has been subjected to ultraviolet irradiation, causing a significant number of mutations in the genome. Which of the following would you NOT expect to occur as a result? A. Activation of the protein kinase ATR B. Activation of the protein kinase Chk1 C. Inactivation of the protein phosphatase Cdc25 D.Binding of p53 to Mdm2 E. Binding of p53 to Mdm2

RRR

A cell's response is not the same when placed on a rigid compared to a soft matrix. Indicate whether each of the following is expected to occur in a cell that is placed on a rigid matrix (R) or a soft matrix (S). Your answer would be a three-letter string composed of letters R and S only, e.g. RSR. ( ) More tension is generated in cell-matrix contacts. ( ) More vinculin proteins would bind to the C-terminal tail of talin. ( ) More actin filaments are recruited to the site of cell-matrix adhesion.

D

A giant aggrecan aggregate can have a molecular mass of 108 daltons or more, and can be as large as a bacterium. Its structure resembles a brush. What is responsible for attaching the bristles of the brush to its core? A. Covalent bonds between aggrecan core protein and keratan or chondroitin sulfate. B. Noncovalent bonds between aggrecan core protein and keratan or chondroitin sulfate. C. Covalent bonds between aggrecan core protein and hyaluronan. D. Noncovalent bonds between aggrecan core protein and hyaluronan.

C

A researcher has coated the wells in a multiwell plate with human plasma fibronectin. She introduces integrin-expressing cells into these wells in the presence of different concentrations of a synthetic peptide. She then washes the wells to remove unbound cells and counts the number of cells that remain attached to each well. The results of her experiment are presented in the following schematic graph. The synthetic peptide sequences used in these experiments were GRGDSPC (1) or GGDRSLN (2). Which one of these peptides (1 or 2) would you expect to correspond to curve a in the graph? Which curve (a or b) would you expect if a synthetic peptide with the sequence GDGRSPC was used? C is cysteine, D is aspartic acid, G is glycine, L is leucine, N is asparagine, P is proline, R is arginine, and S is serine. A. 1; a B. 1; b C. 2; a D. 2; b

1

A researcher has grown monolayers of cells from either of two epithelial cell lines on a permeable supporting membrane that separates two electrolyte chambers. One of the cell lines (A) has been derived from the mammalian kidney and forms epithelial sheets resembling those lining the renal collecting duct and the urinary bladder. The other (B) is derived from the mammalian small intestine. The researcher has measured the voltage (V) and electrical current (I) across the monolayer and has plotted the results in the graph below. Which line (1 or 2) in the graph do you think corresponds to cell line A? Recall that current (I) is related to the applied voltage (V) by the equation I = V/R, in which R is the electrical resistance. Write down 1 or 2 as your answer.

A

Apoptotic cells are efficiently phagocytosed by neighboring cells or macrophages. Which of the following DOES NOT normally happen in this process? A. The apoptotic cell releases some of its cytoplasmic content to induce a local inflammatory response. B. The apoptotic cell exposes phosphatidylserine at its surface, which interacts with receptor proteins on the surface of phagocytes via "bridging" proteins. C. The apoptotic cell loses or inactivates "don't eat me" signals. D. The apoptotic cell rounds up and detaches from its neighbors, which facilitates phagocytosis.

F

Based on the results from your experiment, which force is dominant in chromosome movement in this cell: polar ejection force (E), microtubule flux (F), or kinetochore microtubule plus-end depolymerization (P)?

C

Cadherin molecules at the cell surface are often clustered side-to-side to create a molecular Velcro that attaches the cell to another cell or to the extracellular matrix. In the following simplified drawings, two cells are initially attached via such a Velcro. When one of the cells moves in either of three different ways (A to C), it is faced with a mechanical resistance from the cadherin interactions. The resistance against which type of movement do you think is the weakest? Write down A, B, or C as your answer.

CAB

Cells expressing either N-cadherin (A), high levels of E-cadherin (B), or low levels of E-cadherin (C) have sorted themselves out on a substratum in a cadherin-dependent manner as shown in the schematic drawing below. Which cells (A to C) would you expect to correspond to white, gray, and black in the drawing, respectively? Your answer would be a three-letter string composed of letters A to C only, e.g. CAB.

B

Cellulose is deposited onto the plant cell wall in highly ordered crystalline aggregates by the cellulose synthase complex embedded in the plasma membrane. Would you expect cell wall deposition to continue following treatment of plant cells with a drug that depolymerizes microtubules? Would you expect these cells to be able to switch the orientation of the microfibril pattern between successive lamellae? A. Yes; yes B. Yes; no C. No; yes D. No; no

B

Collagens are extremely rich in ... A. alanine and valine. B. glycine and proline. C. lysine and arginine. D. serine and threonine. E. tyrosine and phenylalanine.

2

Consider a sheet of epithelial tissue that invaginates to form a tube along the anterior-posterior axis of a developing vertebrate embryo. The tube is then closed concomitant with a "convergence and extension" process similar to that observed in germ-band extension in Drosophila melanogaster. During this process, the tube elongates and narrows before pinching off from the sheet. Which axis (1 or 2) in the following schematic drawing of the tube cells do you think corresponds to the anterior-posterior axis? Write down 1 or 2 as your answer.

D

Consider two cells attached to each other via adherens junctions. The forces generated by the actin cytoskeleton in one cell ... A. are dependent on myosin activity. B. are normally balanced by similar forces in the neighboring cell. C. can strengthen the adherens junction by unfolding catenin proteins. D. All of the above.

C

Consider two kinesin motor proteins at the mitotic spindle midzone: kinesin-5 is a tetrameric motor that walks toward the plus end of both microtubules to which it is attached via its motor domains; kinesin-14, on the other hand, walks toward the minus end of one microtubule while it is attached to another microtubule via its tail domain. How do these motors affect the length of the spindle? A. they both work to shorten the spindle B. kinesin-5 works to shorten the spindle whereas kinesin-14 works to lengthen it C. kinesin-5 works to lengthen the spindle whereas kinesin-14 works to shorten it D. they both work to lengthen the spindle

A

Consider two mammalian cells, one in G1 and the other in G0 (stationary) phase. If they are stimulated to pass the restriction point by the addition of an extracellular proliferation signal, but the signal is then immediately removed, what would you expect to happen? A. both cells will replicate their DNA B. only the G1 cell will replicate its DNA C. only the G0 cell will replicate its DNA D. only the G1 cell will start to replicate its DNA, but will stop halfway through the replication and will not reach G2 E. neither of the cells will replicate their DNA

B

EDTA is a metal-ion "chelator" that is commonly used to lower the concentration of free divalent cations in solution. In the lab, your friend has cultured a human cell line on elastic membranes that have been coated with fibronectin and attached to a device that can stretch the membrane. She has quantified the binding of talin to integrin under different conditions, and has presented the results in the following schematic graph, which shows the binding in the presence or absence of EDTA in the cell-culture medium. Which experiment (A or B) do you think was performed in the presence of EDTA? Write down A or B as your answer.

fibroblast

Fill in the blank in the following paragraph regarding the extracellular matrix. Do not use abbreviations. "The extracellular matrix of connective tissues in animals is primarily made and secreted by the __________ family of cells, although they may have more specific names in certain tissues. Being common in connective tissues, these cells can also migrate and proliferate if need be."

desmosomes

Fill in the blank in the following paragraph. Do not use abbreviations. "Particularly abundant in cells of heart muscle and the epidermis, __________ are structurally similar to adherens junctions and contain a number of homologous components. However, their cadherin molecules are linked to intermediate filaments instead of the actin cytoskeleton."

kinetochore

Fill in the blank: The __________ is a large structure formed at the centromeric region of each eukaryotic chromosome. It captures spindle microtubules in mitosis, and therefore serves to attach the chromosomes to the spindle poles.

cytochrome c

Fill in the blank: In the intrinsic pathway of apoptosis, a protein called __________ is released from the mitochondria into the cytosol and binds to the adaptor protein Apaf1, causing it to oligomerize into a wheel-like assembly called an apoptosome, which then recruits initiator caspase-9 proteins.

IIIEE

For each of the following proteins that are proteolytically cleaved in apoptosis, indicate whether the cleavage is first carried out by an initiator (I) or executioner (E) caspase. Your answer would be a five-letter string composed of letters I and E only, e.g. EEEII. ( ) The initiator caspase-2 ( ) The executioner caspase-3 ( ) The BH3-only protein Bid ( ) The endonuclease inhibitor iCAD ( ) The nuclear protein Lamin A

A

Formin nucleates the growth of parallel actin bundles in the cell. Additionally, myosin motor activity is positively regulated by phosphorylation. The monomeric G protein RhoA is important in cytokinesis, because it directly or indirectly ... A. activates formins and inactivates myosin light-chain phosphatase. B. inactivates formins and activates myosin light-chain kinases. C. activates formins as well as myosin light-chain phosphatases. D. inactivates formins as well as myosin light-chain kinases. E. None of the above.1

C

How does talin activate the inside-out signaling through integrin? A. It binds to both integrin subunits to bring them together in an interlocked conformation. B. It is a protein kinase that phosphorylates both integrin subunits and induces activation by conformational change. C. It competes with the α subunit for binding to the β subunit, therefore blocking intimate α-β linkage. D. It binds to the α subunit, and dissociates the dimer into individual subunits that are functionally active.

C

How is Cdc20-APC/C similar to Cdh1-APC/C? A. they are both active throughout interphase B. they are both inhibited by M-Cdk C. they both inhibit M0dk activity D. they are both activated suddenly at the onset of mitosis E. they are both inactivated soon after anaphase

E

How is centrosome duplication similar to DNA replication? A. they both use semiconservative mechanism B. they are initiated at around the same time in the cell cycle, near the G1/S transition C. they are both controlled in such a way that they replicate once and only once per cell cycle D. they are both separated from their sister copies in mitosis E. all of the above

E

How is hyaluronic acid different from other glycosaminoglycans of the extracellular matrix? A. It lacks sulfate groups. B. It is generally not covalently linked to proteins. C. It is not assembled in the Golgi apparatus. D. It can be several megadaltons in mass. E. All of the above.

D

If cells that have started mitosis are treated with nocodazole, a drug that depolymerizes microtubules, what would you expect to happen? Where would you expect Mad2 protein to be localized? A. the cells would arrest in prometaphase; Mad2 would be localized to the spindle poles B. the cells would arrest in telophase; Mad2 would be localized to the spindle poles C. the cells would immediately enter anaphase, finish mitosis, and enter G1; Mad2 would be localized to the spindle poles D. the cells would arrest in prometaphase; Mad2 would be localized to almost all kinetochores E. the cells would arrest in telophase; Mad2 would be localized to almost all kinetochores

C

Imagine a prometaphase chromosome pair that is attached to one spindle pole. Which of the following would happen if both arms of the chromosome are severed with a strong laser beam? A. all chromosome fragments (the centromere-containing fragment and the arm fragements) would be pushed away from the pole B. only the two arm fragments would be pulled toward the pole; the kinetochore-containing fragment would remain stationary C. the kinetochore-containing fragment would be pulled toward the pole; the two arm fragments would move away from the pole D. the kinetochore-containing fragment would move away from the pole, but the two arm fragments would be pulled toward the pole E. all chromosome fragments would be pulled toward the pole

YNYY

In a multicellular organism such as a mammal, loss-of-function mutations in many genes can contribute to the development of cancer. These genes are therefore called tumor suppressors. In their absence, the cell fails to stop progression through the cell cycle under conditions in which normal cells would arrest, paving the way for tumorigenesis. Indicate whether each of the following proteins is (Y) or is not (N) expected to be the product of a tumor suppressor gene based on its function in the cell cycle. Your answer would be a four-letter string composed of letters Y and N only, e.g. YNNN. ( ) Rb ( ) Myc ( ) p53 ()p21

1

In classic experiments carried out in the 1960s and schematized below, an egg of the sand dollar Echinarachnius parma was made into a torus shape using a glass bead on the end of a needle, to study the influence of microtubules on cleavage-furrow positioning. The cells were allowed to undergo two rounds of mitosis. After the second mitosis, an extra furrow (indicated by a red arrowhead) was observed between the two asters that did not have a spindle between them. Which of the models (1 to 3) is more consistent with this observation? Write down 1, 2, or 3 as your answer.

3

In experiments on the flattened eggs of the sea urchin Tripneustes gratilla, cytokinesis was analyzed after placing a small physical barrier (e.g. a glass needle or an oil droplet) between the spindle and various areas of the cell cortex. Blocks that were located over the equatorial plane prevented furrow formation in the proximal membrane, whereas blocks located in other areas did not affect furrowing. Which model (1 to 3) is NOT supported by these results? Write down 1, 2, or 3 as your answer.

D

In insects such as Drosophila melanogaster, electrical synapses are abundant in the ventral nerve cord. Unlike a chemical synapse, the cytosols of pre- and postsynaptic cells in an electrical synapse are connected, allowing action potentials to spread rapidly and without delay. What junctional proteins in the flies are chiefly responsible for this unique feature of the electrical synapses? A. Cadherins B. Claudins C. Connexins D. Innexins E. Integrins

B

In most mammalian cells, low M-cyclin protein levels are maintained during G1 phase. What is mainly responsible for maintaining these low levels? A. Cdc20-APC/C B. Cdh1-APC/C C. Skp2-SCF D. beta-trCP-SCF E. p27

A

In the active state of the integrin dimer, ... A. both intracellular and extracellular binding sites are exposed. B. the intracellular binding sites are inaccessible, while the extracellular binding sites are exposed. C. the intracellular binding sites are exposed, while the extracellular binding sites are inaccessible. D.both intracellular and extracellular binding sites are inaccessible

3

In the early embryos of Caenorhabditis elegans, defects in the formation of astral microtubules increase myosin activity throughout the cell cortex. If the spindle is forced to one side of the cell, the cortical myosin activity is observed mostly at the opposite side of the cell. Which model (1, 2, or 3) better predicts these observations? Write down 1, 2, or 3 as your answer.

BDCA

In the fission yeast Schizosaccharomyces pombe, the proteins Cut1 and Cut2 form a complex that is catalytically inactive. At the onset of anaphase, Cut2 is polyubiquitylated by a large E3 complex containing Cut4, Cut9, Cut23, and other proteins, and is subsequently destroyed. Cut1 then cleaves Rad21, a non-SMC component of a complex that also contains two SMC proteins, thus allowing sister-chromatid separation. Mutations in the cut genes lead to the cut phenotype, in which the cell attempts cytokinesis without chromosome segregation. Indicate which of the following proteins or protein complexes corresponds to or contains the product of the genes cut1 (A), cut2 (B), cut4 (C), and rad21 (D). Your answer would be a four-letter string composed of letters A to D only, e.g. DCAB. ( ) Securin ( ) Cohesin ( ) Anaphase-promoting complex ( ) Separase

C

In the following schematic diagram of a cubic plant cell that has just left the meristem zone, the cellulose microfibrils are shown as black lines. In which direction (1 or 2) do you think the cell will elongate when the cell grows? If the cell wall is momentarily dissolved, in what direction (3 or 4) would water tend to flow? A. 1; 3 B. 1; 4 C. 2; 3 D.2; 4

FACDEB

In the following schematic diagram of a simple columnar epithelium lining the digestive tract, indicate which position (A to F) along the basal-apical axis better corresponds to each of the following features. Your answer would be a six-letter string composed of letters A to F only, e.g. FEDABC. ( ) Basal lamina ( ) Cell apex ( ) Adherens junctions ( ) Gap junctions ( ) Hemidesmosomes ( ) Tight junctions

BC

In the following schematic diagram of a typical eukaryotic cell cycle, choose two major time points (among A to E) at which the cell-cycle control system normally arrests the cycle if DNA damage is detected.

C

In the following schematic diagram of an early Drosophilia embryo, which step (A to C) corresponds to cellularization?

NNEN

In the following schematic diagram of meiotic bivalent in diplotene, indicate whether each of the following chromatid pairs have undergone DNA exchange (E) or not (N). The different color of the final form of chromatid 3 is for clarity only. ( ) chromatids 1 and 3 ( ) chromatids 1 and 4 ( ) chromatids 2 and 3 ( ) chromatids 2 and 4

2

In the following schematic diagram, the estimated attractive or repulsive force between two adhesive cells is plotted as a function of distance between the cells. The dashed curve represents a condition under which the cells express cadherin but not N-CAM. The other two curves represent conditions under which both cadherin and heavily sialylated N-CAM are expressed. In one of the conditions, however, the ionic strength of the medium has been artificially increased by addition of salt. Which curve (1 or 2) do you think represents the high-salt condition? Write down 1 or 2 as your answer.

A

In the following schematic drawing of a vertebrate prometaphase chromosome as seen under a microscope, indicate whether the chromosome is more likely to be closer to pole A or pole B.

C

In the following schematic drawing of connexons as seen from the cytosol of a cell, what is the approximate diameter of each of the pores? Which of the indicated connexons (1 or 2) is more likely to have been incorporated more recently? A. About 20 nm; connexon 1 B. About 4 nm; connexon 1 C. About 1.5 nm; connexon 1 D. About 4 nm; connexon 2 E. About 1.5 nm; connexon 2

D

In the following schematic drawings of aggrecan and decorin, which one (1 or 2) corresponds to aggrecan? Which one (1 or 2) is synthesized primarily by chondrocytes in cartilage? A. 1; 1 B. 1; 2 C. 2; 1 D. 2; 2

WCCW

Indicate whether each of the following descriptions better applies to a Wee1 protein (W) or a Cdc25 protein (C). ( ) it is a protein kinase ( ) it activates M-Cdk complexes ( ) it is activated by M-Cdk complexes ( ) its loss in fission yeast results in small cell size

TGGT

Indicate whether each of the following descriptions better applies to adherens junctions (A), desmosomes (D), gap junctions (G), or tight junctions (T). Your answer would be a four-letter string composed of letters A, D, G, and T only, e.g. AAAD. ( ) They play a direct role in structural polarization of epithelial cells. ( ) They couple cells both electrically and metabolically. ( ) They are formed from hexameric hemichannels that can assemble into heterotypic complexes. ( ) They create semipermeable paracellular pores.

CPPCP

Indicate whether each of the following descriptions better applies to cellulose microfibrils (C) or pectins (P) in plant cell walls. Your answer would be a five-letter string composed of letters C and P only, e.g. CPPPP. ( ) It is made into a network by cross-linking glycans. ( ) It is particularly abundant in the middle lamella. ( ) Divalent ions such as calcium can cross-link it to form gels. ( ) It forms more homogeneous polymers. ( ) It contains many negatively charged galacturonic acid units.

CCEE

Indicate whether each of the following descriptions better applies to connective (C) or epithelial (E) tissues. Your answer would be a four-letter string composed of letters C and E only, e.g. EEEE. ( ) Cells are usually distributed sparsely in the extracellular matrix. ( ) Gap junctions are rarely found. ( ) Direct cell-cell attachments are common. ( ) Cells are tightly associated into sheets.

PFGGGF

Indicate whether each of the following descriptions better applies to glycosaminoglycans (G), fibrous proteins (F), or glycoproteins (P) of the extracellular matrix in animal cells. Your answer would be a six-letter string composed of letters G, F, and P only, e.g. GFPGFP. ( ) They include laminin and fibronectin. ( ) They primarily include collagens. ( ) They include hyaluronan. ( ) They are found in proteoglycans. ( ) They occupy large volumes and form hydrated gels. ( ) They constitute the major proteins of the matrix.

MSMG

Indicate whether each of the following descriptions better applies to mitogens (M), growth factors (G), or survival factors (S). Your answer would be a four-letter string composed of letters M, G, or S only, e.g. GMSG. ( ) They unblock cell-cycle progression ( ) They suppress apoptosis ( ) They trigger a wave of G1/S-Cdk activity ()They inhibit the degradation of cellular macromolecules

IEEE

Indicate whether each of the following descriptions better applies to the intracellular (I) or extracellular (E) domain of integrins. Your answer would be a four-letter string composed of letters I and E only, e.g. EEEE. ( ) It binds to talin. ( ) It binds to the RGD tripeptide motif. ( ) It is bulkier. ( ) It contains divalent cation-binding domains.

WWM

Indicate whether each of the following descriptions better applies to the plant cell wall (W) or the extracellular matrix of animal cells (M). Your answer would be a three-letter string composed of letters W and M only, e.g. WMM. ( ) It is generally thicker and stronger. ( ) It is more rigid. ( ) It has higher nitrogen content.

IPII

Indicate whether each of the following mutations would likely promote (P) or inhibit (I) apoptosis in cells harboring the mutation(s). Your answer would be a four-letter string composed of letters P and I only, e.g. PPPI. ( ) Mutations in the pro-apoptotic effector Bcl2 family proteins Bax and Bak that prevent their association with the outer mitochondrial membrane. ( ) A mutation in the BIR domain of the IAP protein DIAP1 that prevents binding to either caspases or anti-IAP proteins. ( ) A mutation in the anti-IAP protein Reaper that prevents its binding to the IAP proteins. ( ) A mutation in the CARD domain of caspase-9 that prevents its binding to Apaf1.

SGSG

Indicate whether each of the following occurs mainly in G1 phase (G), S phase (S) or G2 phase (H) of the cell cycle. ( ) DNA helicase activation ( ) DNA helicase deposition on DNA at the replication origins ( ) ORC phosphorlyation ( ) licensing of replicated origins

AAAI

Indicate whether each of the following phosphorylation events typically activates (A) or inactivates (I) the protein that is being phosphorylated. ( ) phosphorylation of Cdc25 by M-Cdk ( ) phosphorylation of condensin subunits by M-Cdk ( ) phosphorylation of kinesin-5 by Aurora-A ( ) phosphorylation of Ndc80 subunits by Aurora-B

AIII

Indicate whether each of the following, when active, tends to activate (A) or inactivate (I) M-Cdks. ( ) M-Cdk ( ) Cdc21-APC/C ( ) Cdh1-APC/C ( ) Sic1

B

Initiator and executioner caspases share all of the following features EXCEPT that ... A. they are cysteine proteases (they have a cysteine residue at their active site). B. their inactive form is a monomer. C. they undergo cleavage during activation. D. their active form is a dimer. E. they are inhibited by IAPs.

C

Loss of the gene encoding shugoshin in many multicellular organisms leads to sterility, suggesting defects in meiosis. What would you expect to occur in meiotic cells lacking shugoshin? A. The homologs fail to separate in anaphase I. B. The sister chromatids fail to separate in anaphase II. C. All chromatids separate prematurely in anaphase I. D. Removal of cohesion between homolog arms fails in prophase I. E. Removal of cohesion between sister chromatids fails in prophase II.

E

Malignant cancer cells that have entered the bloodstream can imitate lymphocytes in exiting the bloodstream and entering underlying tissues in the process of metastasis. This "lymphocyte mimicry" can be summarized as ... A. an initial cadherin-dependent rolling followed by an integrin-dependent adhesion and emigration. B. an initial cadherin-dependent rolling followed by an I-CAM-dependent adhesion and emigration. C. an initial cadherin-dependent rolling followed by a selectin-dependent adhesion and emigration. D. an initial selectin-dependent rolling followed by a cadherin-dependent adhesion and emigration. E. an initial selectin-dependent rolling followed by an I-CAM-dependent adhesion and emigration.

I

Mammalian Cdk inhibitor proteins (CKIs) can be grouped into two families based on their structural and functional differences. The Cip/Kip family proteins (e.g. p21) have a broad binding specificity. These proteins bind preferentially to already formed cyclin-Cdk complexes and thus enhance complex formation. However, they inhibit the kinase activity of most complexes (e.g. S-Cdks), except in the case of G1-Cdk complexes where no inhibition occurs. Consequently, Cip/Kip family proteins have an overall positive effect on Cdk4/6 activity due to their help in bringing the subunits together. In contrast, the inhibitors of the INK4 family (e.g. p16) bind only to the Cdk subunit of G1-Cdks and prevent binding of both the G1 cyclins and the Cip/Kip family CKIs. Based solely on these findings, would you expect p16 to activate (A) or inactivate (I) the S-Cdks in the presence of limited amounts of p21?

E

Multidomain glycoproteins in the extracellular matrix have binding sites for many other macromolecules. These glycoproteins ... A. can serve as tracks along which cells can migrate. B. can bind to growth factors and influence cell signaling. C. can bind to cell-surface receptors. D. can serve as repellents to forbid cell migration. E.All of the above.

A

Mutant Saccharomyces cerevisiae cells that lack the gene encoding securin can divide more or less normally by mitosis, without significant chromosome segregation defects. Cells harboring a nondegradable version of securin, on the other hand, arrest in metaphase as expected, since they cannot activate separase to enter anaphase. Similarly, cells lacking Cdc20 arrest in metaphase, since they cannot activate APC/C. Finally, cells lacking both securin and Cdc20 arrest in anaphase: they manage to separate sister chromatids, but do not progress much further. These results suggest that in wild-type cells, ... A. degradation of securin is necessary to trigger sister-chromatid separation. B. degradation of securin is sufficient to trigger sister-chromatid separation. C. Cdc20-APC/C is NOT necessary for sister-chromatid separation. D. Cdc20-APC/C is NOT necessary for later events in anaphase. E. All of the above.

C

Neuromuscular junctions of vertebrates are special types of chemical synapses formed from close association between motor neuron axon terminals and muscle fibers. A thin layer of basal lamina separates the two cell membranes at the neuromuscular junction and is important for its organization and maintenance. Which of the following would you NOT expect to find in the basal lamina in these structures? A. Nidogen B. Laminin C. Type I collagen D. Type IV collagen E. Perlecan

D

Overproduction of cadherins such as E-cadherin ... A. is often found in cancers originating from epithelia. B. is induced by the transcription regulatory protein Twist. C. induces epithelial-mesenchymal transition. D. leads to stronger cell-cell adhesion. E. All of the above.

C

Plasmodesmata in plant cells are functionally similar to animal cells' ... A. adherens junctions. B. desmosomes. C. gap junctions. D. hemidesmosomes. E. tight junctions.

T

Platelets that express a constitutively active Rap1 are able to activate integrins even in the absence of thrombin stimulation. In contrast, cells expressing a binding-deficient version of talin are unable to perform integrin activation. In platelets expressing both of these mutant proteins, what would you expect to observe: the Rap1 gain-of-function phenotype (R) or the talin loss-of-function phenotype (T), as described above? Write down R or T as your answer.

B

Resveratrol is a natural compound found in red grapes (and red wine) and is thought to have beneficial effects in mammals, such as preventing tumor growth and delaying age-related diseases. In vitro, resveratrol and its derivatives have been shown to cause cell-cycle arrest in S phase and induce apoptosis. You have analyzed the DNA content of cultured cells in the presence and absence of these drugs using fluorescence-activated cell sorting. Compared with control cells (dashed line), which of the following curves do you think better represents the DNA content of cells treated with these compounds?

D

Selectins ... A. mainly mediate cell-matrix attachments. B. are members of the Ig superfamily of cell adhesion molecules. C. do NOT require Ca2+ for their adhesive function, unlike integrins. D. are carbohydrate-binding proteins. E. All of the above.

D

Soon after the discovery of nerve growth factor (NGF), researchers injected newborn mice with rabbit antiserum (i.e. serum that contains antibodies) against NGF. They observed massive nerve cell death compared to appropriate control injections. Up to 99% of the neurons in some parts of the developing peripheral nervous system died after about a week of daily injections. These results suggest that ... A. NGF signaling sensitizes developing nerve cells to apoptotic signals. B. developing neurons undergo apoptosis in the presence of rabbit proteins. C. developing neurons require NGF for apoptosis. D. developing neurons undergo cell death in the absence of NGF. E. NGF signaling is sufficient for survival of the developing neurons.

CFEDAB

Sort the following schematic diagrams (A to F) to reflect the order of events in a typical eukaryotic M phase. An interphase cell in G2 phase is drawn on the left for comparison.

FTFF

T or F: ( ) Apoptosis is the final fate of almost all cells in an adult animal. ( ) Even perfectly healthy cells may undergo apoptosis. ( ) DNA damage that cannot be repaired inhibits apoptotic pathways. ( ) Apoptosis is the main form of programmed cell death in plant cells as well as in animal cells.

FTTF

T or F: ( ) Cadherins are present in all multicellular organisms. ( ) Adhesion by cadherins is dependent on Ca2+ ions. ( ) In contrast to nonclassical cadherins, classical cadherins are more closely related in sequence. ()E, N, and P cadherins are mainly found in desmosomes.

TFTF

T or F: ( ) Either excessive or insufficient apoptosis can contribute to disease. ( ) Excessive apoptosis, in many cases, leads to autoimmune disease and cancer. ( ) In about half of human cancers, the tumor suppressor protein p53 is mutated. ()Drugs that interfere with the function of Bcl2 family proteins such as Bax and Bak may treat cancers by stimulating apoptosis.

TFFT

T or F: ( ) Fibronectin carries asparagine-linked oligosaccharides. ( ) Fibronectin often forms homodimers by cross-linking through covalent attachment of lysine residues. ( ) Fibronectin binds to integrins, collagens, and glycosaminoglycans through its type III repeats. ()Fibronectin molecules can assemble into fibrils only in the vicinity of cells.

FTTT

T or F: ( ) Integrins are the only known matrix receptors in animal cells. ( ) Integrins can transmit signals in both directions across the membrane; that is, both outside-in and inside-out. ( ) Tension can increase the binding affinity of an integrin for its intracellular and extracellular ligands. ( ) Integrins can convert molecular signals into mechanical ones.

FFTT

T or F: ( ) Integrins usually bind their ligands with a higher affinity compared to other cell-surface receptors. ( ) Unlike cadherins, integrins usually function as individual dimers and do not cluster. ( ) Anchorage dependence is mainly mediated via integrin signaling. ( ) Integrins can activate the Ras-MAPK pathway.

FFFF

T or F: ( ) Replicative cell senescence usually arises due to the accumulation of mutations in genes encoding S- and M-cyclins. ( ) Replicative cell senescence is caused by the induction of apoptosis by p53. ( ) Excessive mitogenic stimulation can result in Mdm2 activation and the induction of apoptosis or cell-cycle arrest. ( ) The Mdm2 inhibitor Arf induces cell-cycle progression.

FTTF

T or F: ( ) They are highly branched polysaccharides. ( ) They are strongly hydrophilic and absorb a large amount of water. ( ) They all contain N-acetylglucosamine or N-acetylgalactosamine. ( ) They are highly positively charged.

FTTF

T or F: ( ) bivalents form before prophase I ( ) crossing-over begins before the synaptonemal complex assembly ( ) chiasmata can first be seen under the microscope after the disassembly of the synaptonemal complexes ( ) all recombination events lead to crossovers

FTTT

T or F: ( ) microtubules become greatly stabilized in mitosis compared to interphase ( ) the number of y-tubulin ring complexes in the centrosomes increases greatly during mitosis compared to interphase ( ) chromosomes stabilize mitotic microtubules through activation of Ran monomeric G protein ( ) a bipolar spindle can be formed even in the absence of centrosomes

FFFF

T or F: ( ) the force for cytokinesis is generated by kinesis motors on microtubule bundles that form the contractile ring ( ) as the contractile ring constricts, its thickness increases to keep a constant volume ( ) the midbody forms from bundles of actin and myosin II ( ) local activation of Ran GTPase triggers the assembly and contraction of the contractile ring

TTTF

T or F: ( ) the preprophase band, composed of microtubules and actin filaments, marks the site of cytokinesis in plant cells ( ) in some cell types, the site of contractile-ring formation is determined before mitosis ( ) the early cell plate in dividing plant cells appears after phragmoplast formation ( ) the membrane required for the newly formed cell plate in plant cells is provided by endocytosis from the equatorial plasma membrane

BAE

The Bcl2 family is comprised of anti-apoptotic (A), BH3-only (B), and effector (E) proteins. In the following diagram representing the regulation of the intrinsic pathway of apoptosis, what class of activated Bcl2 family proteins (A, B, or E) corresponds to boxes 1 to 3, respectively? Your answer would be a three-letter string composed of letters A, B, and E only, e.g. ABE.

D

The cell cycle can be arrested in mitosis when a single sister-chromatid pair is mono-oriented on the mitotic spindle. If at this point a glass microneedle is used to pull the mono-oriented chromosome toward the pole to which it is not attached, the cell proceeds to anaphase. This observation confirms that ... A. mono-oriented chromosomes are stable B. mechanical tension drives the formation of bi-oriented chromosomes C. bi-oriented chromosomes activate the spindle assembly checkpoint D. lack of mechanical tension at the kinetochore in at least one chromosome prevents entry into anaphase E. mechanical tension at the kinetochore in at lease one chromosome is required for entry into anaphase

CD

The chemical compound PMA is a potent stimulator of the epithelial-mesenchymal transition in epithelial cells. The activity of two of the following types of proteins is typically up-regulated in epithelial cells treated with PMA, while that of the other two is mainly down-regulated. Choose the two proteins whose activity you think is stimulated by PMA. Your answer would be a two-letter string composed of letters A to D only in alphabetical order, e.g. BC. (A) Cadherin (B) Connexin (C) Matrix metalloprotease (D) Integrin

1

The elasticity of the components of the extracellular matrix can be visualized in a stress-strain curve, in which the tensile stress (corresponding to load) applied to a tissue sample is plotted against the strain (corresponding to deformation) measured in the tissue. In the following stress-strain graph, the elasticity of an intact connective tissue is represented by a dashed curve. The other two curves correspond to the same tissue that has been treated with either formic acid (to digest collagen) or trypsin (to digest elastin). Which curve (1 or 2) do you think corresponds to trypsin treatment?

C

The focal adhesion kinase ... A. is a cytosolic serine/threonine kinase. B. binds directly to integrin dimers. C. can be phosphorylated by Src kinases. D. prevents the relay of outside-in integrin signaling. E.All of the above.

CBDA

The following schematic diagram shows the activation of M-Cdk in mitosis. Indicate which proteins below correspond to those indicated as A to D in the diagram. ( ) Wee 1 ( ) CAK ( ) Cdc25 ( ) M-cyclin

A

The following schematic drawing shows two integrin molecules. Which molecule (a or b) is depicted in its active configuration? Which side of the plasma membrane (1 or 2) represents the cytosol? A. a; 1 B. a; 2 C. b; 1 D. b; 2

A

The microtubule-binding protein Patronin binds to the minus ends of microtubules at the spindle pole and protects them from the effect of catastrophe factors. If Patronin activity is inhibited by injecting an anti-Patronin antibody into Drosophila melanogaster embryos prior to cellularization, anaphase B is suppressed and the spindles are significantly shorter. Which of the forces (1 or 2) in the following schematic diagram do you think is mostly responsible for anaphase B in this organism at this stage? Does the effect of Patronin inhibition resemble that of kinesin-5 inhibition (I) or overactivation (O)? A. 1; I B. 1; O C. 2; I D. 2; O

D

The size distribution of exons coding for collagen helical domains in various vertebrates reveals a unique pattern. This pattern provides clues to the evolutionary history of the genes encoding fibrillar collagen α chains. What is this pattern? A. The length of most exons is a multiple of 100 nucleotides. B. Most exons code for 54, or a multiple of 54, Gly-X-Y repeats. C. The length of most exons is a multiple of 30 nucleotides. D. Most exons code for 6, or a multiple of 6, Gly-X-Y repeats. E.None of the above.

C

This large glycoprotein of the extracellular matrix is associated with elastin fibers and is essential for their integrity. Its deposition in the developing connective tissues often precedes the appearance of elastin. It is part of microfibrils that cover the elastic fibers. This protein is ... A. collagen. B. fibronectin. C. fibrillin. D. filamin. E. laminin.

NEXT THREE QUESTIONS

Three models for contractile-ring positioning in animal cells are presented in the schematic diagrams below. Answer the following question(s) according to these models.

A

To study chromosome movement during anaphase in mammals, you have injected fluorescently labeled tubulin subunits into cells such that microtubules can be seen under a fluorescence microscope. You then use a relatively strong laser beam to bleach the fluorescent dyes in a limited area of a metaphase cell, as indicated in the schematic diagram below, and follow the progression of mitosis under the microscope by time-lapse imaging. You then use the images to measure the change in distance between various components, and plot the results in the graph below. Answer the following question(s) based on these results. Based on the results from the experiment, which is dominant in this cell: anaphase A or anaphase B?

E

Treatment of dividing cells with a low dose of the antifungal drug benomyl, which destabilizes microtubules, slows down correct spindle assembly. But at such doses, the spindle is eventually formed and the cells survive. However, mutations in some genes confer benomyl sensitivity: the mutant cells die because they fail to arrest the cell cycle in the presence of unattached kinetochores and progress through anaphase, with disastrous consequences. Which of the following would you expect to be a benomyl-sensitive mutant? A. A loss-of-function mutant in the gene encoding Mad2. B. A mutation causing the overexpression of Cdc20. C. A loss-of-function mutation in the gene encoding a kinase that inhibits Cdc20-APC/C. D. A loss-of-function mutation in the gene encoding a tubulin subunit. E. All of the above.

C

Type IV collagen molecules can interact at their C-termini to form dimers and at their N-termini to form tetramers. What category do you think this type of collagen belongs to? A. Fibrillar B. Fibril-associated C. Network-forming D. Proteoglycan core E. Anchorage fibril

C

What is the most common additional polymer present in the plant secondary, but not primary, cell wall? A. Cellulose B. Pectin C. Lignin D. Starch

A

Which collagens are the most common in our body? A. Fibrillar B. Fibril-associated C. Network-forming D. Proteoglycan core E. Anchorage fibril

D

Which components of the extracellular matrix are mostly responsible for its ability to resist compressive and tensile forces, respectively? A. Collagens and glycoproteins B. Glycoproteins and collagens C. Glycosaminoglycans and glycoproteins D. Glycosaminoglycans and collagens E. Collagens and glycosaminoglycans

D

Which division in meiosis is more similar to mitosis? In which division do sister chromatids separate from each other? A. meiosis I; meiosis I B. meiosis I; meiosis II C. meiosis II; meiosis I D. meiosis II; meiosis II

B

Which of the following cell junctions uses cadherin cell adhesion molecules to anchor the actin cytoskeleton? A. Tight junction B. Adherens junction C. Desmosome D. Hemidesmosome E. Gap junction

D

Which of the following cell populations in our body has the highest mitotic index? A. Neurons B. Hepatocytes C. Red blood cells D. Fibroblasts E. Skeletal myocytes

E

Which of the following events contributes to driving the mammalian cell past the restriction point of the cell cycle? A. Phosphorylation of Cdh1-APC/C by G1/S-Cdk B. Destruction of CKIs that target S-Cdks C. Phosphorylation of Rb by G1-Cdk, G1/S-Cdk, and S-Cdk D. Activation of E2F gene expression by active E2F protein E. All of the above

C

Which of the following events occurs at the onset of S phase in a mitogen-stimulated vertebrate cell? A. Activation of Cdh1-APC/C B. Activation of Rb C. Activation of geminin D. Activation of Cdc20 E. All of the above

D

Which of the following events occurs in mitotic metaphase? A. nuclear envelope breakdown B. nuclear envelope reassembly C. chromosome attachment to spindle microtubules for the first time D. chromosome alignment at the spindle equator E. mitotic spindle

D

Which of the following extracellular matrix components contains a transmembrane protein? A. Type I collagen B. Perlecan C. Aggrecan D. Syndecan E. Decorin

E

Which of the following is NOT an anchoring junction? A. Adherens junction B. Desmosome C. Actin-linked cell-matrix junction D. Hemidesmosome E.Tight junction

B

Which of the following is an inhibitory extracellular signal for cell proliferation? A. EGF B. TGFβ C. Erythropoietin D. IGF E. PDGF

A

Which of the following is more directly by active M-Cdk? A. centrosome maturation B. centrosome duplication C. nuclear envelope reassembly D. inactivation of APC/C E. cell cleavage

C

Which of the following is true regarding fibril-associated collagens such as type IX collagen? A. They aggregate with one another to form long fibrils in the extracellular space. B. They lack the triple-stranded helical structure found in other collagens. C. They are more flexible than collagens of types I to IV. D. They are the most common among collagens. E. All of the above.

D

Which of the following molecules is capable of tension-sensing by exposing binding sites for other proteins when mechanically stretched? A. α-Catenin B. Talin C. Fibronectin D. All of the above

C

Which of the following morphological changes is NOT typically seen in a cell that is undergoing apoptosis? A. The cell rounds up. B. The nuclear envelope disassembles. C. The cell swells. D. Large cells break up into membrane-enclosed fragments. E. The nuclear chromatin breaks into fragments.

E

Which of the following motor proteins are more directly involved in anaphase B? A. Kinesin-5 on interpolar microtubules and dynein on kinetochore microtubules B. Kinesin-13 on kinetochore microtubules and dynein on astral microtubules C. Kinesins 4 and 10 on interpolar and astral microtubules and dynein on kinetochore microtubules D. Kinesin-5 on interpolar microtubules and kinesins 4 and 10 on interpolar and astral microtubules E. Kinesin-5 on interpolar microtubules and dynein on astral microtubules

E

Which of the following proteins activates the mitochondrial pathway of apoptosis? A. The tumor suppressor protein p53, when activated in response to extensive DNA damage. B. The BH3-only protein Bid, when cleaved by the initiator caspase-8 (from the extrinsic pathway). C. The anti-IAP protein Omi, when activated by dephosphorylation. D. The BH3-only protein Bad, when activated by dephosphorylation. E. All of the above.

C

Which of the following proteins is the product of an immediate early gene expressed following mitogenic stimulation of cell-cycle entry? A. E2F B. Rb C. Myc D. G1-cyclins E.All of the above

A

Which of the following simplified diagrams better shows the changed in the concentrations of three major cyclin-Cdk complexes (G1/S-Cdk, S-Cdk, and M-Cdk) in the cell in different stages of the cell cycle?

B

Which of the time points (A to E) in the following schematic drawing of the mammalian cell cycle represents the restriction point?

B

Which one better supports cell proliferation when added to fibroblast cultures: serum or plasma? This activity is due to the presence of mitogens in this fluid. What is responsible for making these mitogens? A. Serum; red blood cells B. Serum; platelets C. Plasma; red blood cells D. Plasma; white blood cells E. Plasma; platelets

A

Which one of the FACS plots (a or b) would you expect to correspond to the loss-of-function p21 mutants?

C

Which one of the following chromosomes has formed stable attachment(s) to the spindle microtubules?

A

Which stage is usually the longest in meiosis? A. prophase I B. prometaphase I C. telophase I D. prophase II E. prometaphase II

213

You have been studying the the effect of loss-of-function mutations in the Cdk inhibitor protein (CKI) p21. You add the drug fucoxanthin to cell cultures harboring either wild-type or mutant versions of the p21 gene. Fucoxanthin is known to induce cell-cycle arrest in G1. After a day, you add the thymidine analog BrdU to the culture media, collect the cells after an hour, treat them with anti-BrdU antibody and the fluorescent DNA stain DAPI, and finally subject them to fluorescence-activated cell sorting (FACS). The FACS data can be viewed as a two-dimensional dot plot composed of thousands of dots, in which each cell is represented by one dot at coordinates that correspond to the intensities of the DAPI fluorescence signal (X axis) and BrdU fluorescence signal (Y axis) for that cell. Anser the following questions according to the simplified dot plot below, generated from your experiment. Indicate which boxed region (1, 2, or 3) in the FACS plots corresponds better to each of the following phases of the cell cycle. ( ) G1 phase ( ) S phase ( ) G2 and M phases

1

You have isolated epithelial cells from mouse mammary glands and have grown them in a three-dimensional gelatinous matrix in the presence or absence of a specific inhibitor that targets a transmembrane metalloprotease. The protease is capable of cleaving cadherin near the base of its extracellular domain to release an N-terminal fragment containing the extracellular cadherin domains. The distribution of the cells in the matrix, as seen under a light microscope, one day after the transplantation of the isolated tissue is presented in the following schematic drawings. Which condition (1 or 2) do you think corresponds to the presence of the protease inhibitor? Write down 1 or 2 as your answer.

D

You have synchronized a culture of HeLa cells so that the cells are all at the same stage in the cell cycle. You then treat the cells with serum containing nutrients and growth factors in the presence or absence of the drug rapamycin. The distribution of cell sizes in the two cell populations is shown below. Based on these results, do you think rapamycin is an activator or inhibitor of the TOR complex? Is the S6 kinase expected to be up-regulated or down-regulated in the presence of rapamycin? A. Activator; up-regulated B. Activator; down-regulated C. Inhibitor; up-regulated D. Inhibitor; down-regulated

B

v-FLIPs are viral proteins that were first identified as modulators of apoptosis; they contain two death effector domains, which are also found in some initiator caspases such as procaspase-8. These v-FLIP proteins can be recruited to the DISC through the binding of the death effector domain to similar domains in the adaptor proteins, but are otherwise catalytically inactive. What do you think is the effect of v-FLIP expression in the host cell? A. It promotes apoptosis mainly via the extrinsic pathway. B. It inhibits the extrinsic pathway of apoptosis. C. It activates only the mitochondrial pathway of apoptosis. D. It inhibits the intrinsic pathway of apoptosis. E. It enhances the caspase cascades in both the intrinsic and extrinsic pathways.