Test 4 MB HW
Sterility in human males with Kartagener's triad is due to non motile sperm. Upon cytological examination, the sperm of such individuals are found to have tails (that is, flagella) that lack one or more of the normal structural components. Such individuals are also likely to have histories of respiratory tract disease, especially recurrent bronchitis and sinusitis, caused by an inability to clear mucus from the lungs and sinuses. 1. What is a likely mechanistic explanation for nonmotility of sperm in such cases of sterility? 2. Why is respiratory tract disease linked with sterility in affected individuals?
1. A structural defect in the outer dynein arms of the sperm tail axoneme, causing the sperm tail (or flagellum) to be nonfunctional. 2. The same structural defects in the sperm tail are also likely to affect the cilia responsible for sweeping mucus and foreign matter out of the lungs and sinuses.
Fibroblasts can be placed on thin sheets of silicone rubber. Under normal circumstances, fibroblasts exert sufficient tension on the rubber so that it visibly wrinkles. Explain how the ability of fibroblasts to wrinkle rubber would compare with that of normal cells under the following conditions. 1. The cells are injected with large amounts of purified gelsolin. 2. The cells are treated with a permeable form of C3 transferase, a toxin from the bacterium, Clostridium botulinum, which covalently modifes an amino acid in Rho by ADP-ribosylation. This renders Rho unable to bind to proteins that it would normally bind to when active. 3. The cells are treated with taxol. 4. The cells are treated with latrunculin A, the drug is washed out, and the cells are observed periodically. 5. A constitutively activated Rho is introduced into the cell.
1. Gelsolin severs microfilaments, resulting in loss of tension-generating elements, so wrinkling should decrease. 2. Decreasing Rho activity by adding C3 transferase should decrease contractility by decreasing the number of stress fibers. This causes a reduction in wrinkles. 3. Taxol stabilizes microtubules, which are thought to bear compressive loads. Now the cells should be better able to resist their own tension, and the wrinkling of the rubber should be less pronounced. 4. Latrunculin A would cause the loss of F-actin, resulting in the same effects as in loss of tension-generating elements, so wrinkling should decrease. After the drug is washed out, contractility should eventually resume, as sufficient microfilaments form to allow force production. 5. A constitutively active Rho would cause excess contraction, leading to more wrinkles.
Scurvy is a disease that until the nineteenth century was common among sailors and others whose diets were deficient in vitamin C (ascorbic acid). Individuals with scurvy suffer from various disorders, including extensive bruising, hemorrhages, and breakdown of supporting tissues. Ascorbic acid serves as a reducing agent responsible for maintaining the activity of prolyl hydroxylase, the enzyme that catalyzes hydroxylation of proline residues within the collagen triple helix, which is required for helix stability. 1. Based on this information, postulate a role for hydroxyproline in collagen triple helices. 2. Construct the sequence of events leading from a dietary vitamin C deficiency to symptoms such as bruising and breakdown of supporting tissues. Rank the events from the first to the last. 3. Can you guess why sailors are no longer susceptible to scurvy? 4. Why do you think British sailors are called "limeys" to this day?
1. Hydroxylated proline residues, but apparently not non-hydroxylated proline residues, but apparently not non hydroxylated proline residues, stabilize the collagen triple helix. The hydroxyl groups of this amino acid form interchain hydrogen bonds that help stabilize the assembled triple-stranded helix. 2. tissue levels of ascorbic acid is low enzyme prolyl hydroxylase is inactive proline is not hydroxylated the triple helix is inadequately stabilized collagen breaks down defects in tissues that depend on collagen tissues that depend on collagen are subject to breakdown and bruising 3. Fresh fruits (vitamin C source) are available now. 4. The term reflects the British Navy's use of limes.
Where in the cell is the tag incorporated into the protein? 1. The short peptide Lys-Asp-Glu-Leu 2. Hydrophobic membrane-spanning domains 3. Mannose-6-phosphate
1. Incorporated into ER-specific proteins as the polypeptides are synthesized by ribosomes attached to the rough ER. 2. Incorporated into membrane-bound Golgi complex proteins as the polypeptides are synthesized by ribosomes attached to the rough ER. 3. Residues are attached to soluble lysosomal proteins by the sequential action of several enzymes found in the lumen of the rough ER and Golgi complex.
Indicate whether each of the following descriptions is true of microtubules (MT), microfilaments (MF), intermediate filaments (IF), or none of these (N). More than one response may be appropriate for some statements.
1. Involved in muscle contraction. - MF 2. Involved in the movement of cilia and flagella. - MT 3. More important for chromosome movements than for cytokinesis. - MT 4. More important for cytokinesis than for chromosome movements in animal cells. - MF 5. Most likely to remain when cells are treated with solutions of nonionic detergents or solutions of high ionic strength. - IF 6. Structurally similar proteins are found in bacterial cells. - MT, MF, and IF 7. Their subunits can bind and catalyze hydrolysis of phosphonucleotides. - MT and MF 8. Can be detected by immunofluorescence microscopy. - MT, MF, and IF 9. Play well-documented roles in cell movement. - MT and MF 10. The fundamental repeating subunit is a dimer. - MT and IF
Explain how the various domains of the fibronectin molecule or the laminin molecule are important for their function? 1. Fibronectin 2. Laminin 3. Both Fibronectin and Laminin
1. It can bind to fibrin (important during blood clot formation), and can bind to collagen or heparan sulfate proteoglycans for attaching it to the ECM. The RGD-containing cell-binding domain is crucial for allowing cells to attach to this molecule, because this is the site that is bound by integrins on the cell surface. 2. It has an integrin-binding site specific for _6_1 integrins. A collagen IV binding site allows it to be attached to the basal laminae (where the molecule is predominantly found). 3. It has multiple domains that allow to attach to other ECM proteins.
Each of the following processes is associated with one or more specific eukaryotic organelles. In each case, identify the organelle or organelles. 1. β oxidation of long-chain fatty acids 2. Biosynthesis of cholesterol 3. Biosynthesis of insulin 4. Biosynthesis of testosterone or estrogen 5. Degradation of damaged organelles 6. Glycosylation of membrane proteins 7. Hydroxylation of phenobarbital 8. Sorting of lysosomal proteins from secretory proteins
1. It is associated with peroxisomes and mitochondria. 2. It is associated with smooth endoplasmic reticulum. 3. It is associated with rough endoplasmic reticulum and Golgi. 4. It is associated with smooth endoplasmic reticulum. 5. It is associated with lysosome 6. It is associated with rough endoplasmic reticulum and Golgi. 7. It is associated with smooth endoplasmic reticulum. 8. It is associated with Golgi.
For each of the following statements, indicate whether it is true of the motility system that you use to lift your arm, to cause your heart to beat, to move ingested food through your intestine, or to sweep mucus and debris out of your respiratory tract. 1. It depends on muscles that have a striated appearance when examined with an electron microscope. 2. It would probably be affected by the same drugs that inhibit motility of a flagellated protozoan. 3. It requires ATP. 4. It involves calmodulin-mediated calcium signaling. 5. It involves interaction between actin and myosin filaments. 6. It depends heavily on fatty acid oxidation for energy. 7. It is under the control of the voluntary nervous system.
1. It is true of the motility system that you use to lift your arm. It is true of the motility system that you use to cause your heart to beat. 2. It is true of the motility system that you use to sweep mucus and debris out of your respiratory tract. 3. It is true of the motility system that you use to lift your arm. It is true of the motility system that you use to cause your heart to beat. It is true of the motility system that you use to move ingested food through your intestine. It is true of the motility system that you use to sweep mucus and debris out of your respiratory tract. 4. It is true of the motility system that you use to move ingested food through your intestine. 5. It is true of the motility system that you use to lift your arm. It is true of the motility system that you use to cause your heart to beat. It is true of the motility system that you use to move ingested food through your intestine. 6. It is true of the motility system that you use to cause your heart to beat. 7. It is true of the motility system that you use to lift your arm.
Plants and animals are made up of billions of cells. These cells are surrounded by extracellular components that facilitate their interactions and provide a suitable environment for the construction and protection of tissues. The cellular organization and extracellular environments of plants and animals are very different.
1. Membrane protein complexes that strengthen the adhesion between adjacent cells, like rivets, to protect against pulling forces--desmosomes, animal 2. Small channels that for across the plasma membranes of adjacent cells; especially important in intercellular communication-- gap junctions, animal 3. Membrane proteins that create a watertight seal between cells-- tight junctions, animal 4. Small channels between cells that are otherwise surrounded by walls; enable movement of water and solutes between cells-- plasmodesmata, plant 5. A polysaccharide that is used to synthesis cell walls, which protect cells and help maintain their shape-- cellulose, plant 6. Long fibers of protein found in the extracellular matrix that provide structural support for cells-- collagen, animal
Polarized cytoskeletal structures and intraflagellar transport (IFT) are involved in formation of cilia and flagella. 1. Observation of flagella in the biflagellate alga, Chlamydomonas reinhardtii, indicates that particles move toward the tips of flagella at a rate of , but the particles moving back toward the base of flagella move at . How do you explain this difference in rate of movement? 2. Temperature-sensitive mutations in a kinesin II required for intraflagellar transport (IFT) have been identified in Chlamydomonas. Such mutations only lead to defects when the temperature is raised above a certain threshold, called the restrictive temperature. When algae with fully formed flagella are grown at the restrictive temperature, their flagella degenerate. What can you conclude about the necessity of IFT from this experiment? 3. Based on your knowledge of the directionality of microtubule motors and the information in part B, where would you predict that the plus ends of flagellar microtubules are? State your reasoning.
1. Particles use different motors with different velocities to move outward and inward. 2. IFT seems to be necessary for ongoing maintenance of flagellar structure. 3. Kinesins transport cargoes toward the plus ends of microtubules, so the plus ends should be at the tip of the flagellum.
Described here are the results of several recent studies on the proteins of the cytoskeleton. In each case, state the conclusion(s) that can be drawn from the findings. 1. Small vesicles containing pigment inside of pigmented fish epidermal cells aggregate or disperse in response to treatment with certain chemicals. When nocodazole is added to cells in which the pigment granules have been induced to aggregate, the granules cannot disperse again. 2. When an animal cell is treated with colchicine, its microtubules depolymerize and virtually disappear. If the colchicine is then washed away, the MTs appear again, beginning at the centrosome and elongating outward at about the rate (1μm/min) at which tubulin polymerizes in vitro. 3. Extracts from nondividing frog eggs in the G2 phase of the cell cycle were found to contain structures that could induce the polymerization of tubulin into microtubules in vitro. When examined by immunostaining, these structures were shown to contain γ-tubulin.
1. Pigment granule dispersal is a microtubule-dependent process. 2. The centrosome serves as a microtubule-organizing center in vivo, and all of the microtubules radiating from the centrosome apparently have the same polarity. 3. The extracts appear to contain structures that are functionally equivalent to centrosomes (as evidenced by the presence of γ-tubulin), which nucleate micro-tubule growth.
Where would the protein likely go if you were to remove the tag? 1. The short peptide Lys-Asp-Glu-Leu 2. Hydrophobic membrane-spanning domains 3. Mannose-6-phosphate
1. Removal of this tag from ER-specific proteins usually results in their secretion from the cell. 2. Removal of this tag would convert the membrane-bound proteins to soluble proteins and would also severely affect folding of the polypeptides; such abnormal proteins will probably be exported from the ER and degraded. 3. Removal of residues from lysosomal proteins often leads to secretion of the proteins; however, evidence suggests that additional tags may ensure delivery of some lysosomal proteins to endosomes.
How does the tag ensure that the protein reaches its destination? 1. The short peptide Lys-Asp-Glu-Leu 2. Hydrophobic membrane-spanning domains 3. Mannose-6-phosphate
1. When such proteins reach the Golgi complex, they bind to specific receptors and are packaged into transport vesicles for return to the ER. 2. Such proteins tend to move through the endomembrane system until the thickness of the membrane, which increases progressively from the ER to the plasma membrane, exceeds the length of their domains and blocks further migration. 3. When such proteins reach the trans-Golgi network, they bind to receptors and are packaged into vesicles for transport to endosomes.
Indicate the role each protein plays in the junction. 1. Connexin 2. E-cadherin 3. Desmocollins 4. Desmotubule 5. Desmoplakin 6. Annulus 7. α-Catenin 8. Claudins
1. forms channels (cytoplasmic connections) between adjacent animal cells. 2. transmembrane adhesive connections between two adjacent animal cells. 3. the desmosomal cadherins that probably bind the plasma membranes of the two cells together. 4. tubular structure found in the center of a plasmodesmata. 5. major proteins of the desmosome plaque. 6. forms channels (cytoplasmic connections) between adjacent plant cells. 7. anchors actin microfilaments to the plasma membrane. 8. binds adjoining cells together, creating fused ridges.
Indicate whether each of the following proteins or structures is a component of adherens junctions, desmosomes, tight junctions, gap junctions, or plasmodesmata. 1. Connexin 2. E-cadherin 3. Desmocollins 4. Desmotubule 5. Desmoplakin 6. Annulus 7. α-Catenin 8. Claudins
1. gap junctions 2. adherens junctions 3. desmosomes 4. plasmodesmata 5. desmosomes 6. plasmodesmata 7. adherens junctions 8. tight junctions
The various parts of the endomembrane system serve different functions in the cell. In this activity, you will identify the roles of each part of the endomembrane system. 1. smooth ER 2. rough ER 3. Golgi apparatus 4. Lysosomes
1. lipid synthesis calcium ion storage poison detoxification 2. protein synthesis 3. protein modification and sorting cisternal maturation 4. macromolecule digestion autophagy
Sort the phrases into the appropriate bins depending on whether they describe exocytosis, endocytosis, or both. 1. Exocytosis 2. Endocytosis 3. Both
1. secretes large molecules out of the cell increases the surface area of the plasma membrane requires fusion of vesicles with the plasma membrane 2. forms vesicles from inward folding of the plasma membrane decreases the surface area of the plasma membrane 3. requires cellular energy transported substances never physically cross the plasma membrane
The critical concentration of GTP-tubulin heterodimers in vitro has been measured and found to be 200 nanomolar and 1000 nanomolar for the plus and minus ends, respectively. Which of the following GTP-tubulin heterodimer concentrations would favor treadmilling?
650 nanomolar
Imagine that you are a cellular biologist studying the processing of a lysosomal protein. When you mutate a specific amino acid in its sequence, the protein accumulates in the trans cisternae of the Golgi complex and is NOT transported to the lysosome. What is a possible cause of this?
A glycosylation site has been removed.
How can cell death continue almost indefinitely, even after prevention of further exposure to silica dust or asbestos fibers? Drag the terms on the left to the appropriate blanks on the right to complete the sentences.
Because the fibers and particles are not digestible and there is no mechanism to remove them from the lungs, a cycle of uptake, lysosomal damage, cell death, and fiber or particle release is set up that can continue indefinitely, killing more and more cells.
Which of the following is the most accurate summary concerning the common adhesive glycoproteins of the ECM, fibronectins, and laminins?
Both of these proteins are extremely large adaptor-like proteins, containing multiple domains that serve as attachment sites for collagen, heparin, heparan sulfate, and cell-surface receptors.
A researcher is attempting to isolate rough ER microsomes using ultracentrifugation. Which of the following would indicate contamination of the rough ER with another organelle?
Catalase
How might you explain the death of silica-containing or asbestos-containing cells?
Cell death is probably due to the digestion of cellular components by acid hydrolases that escape from damaged lysosomes.
Which of the following must be true concerning chemotaxis?
Chemotaxis must be sensitive to inhibitors, antagonists, and agonists.
In many people, the ingestion of ethanol produces a dose-dependent leakage of interstitial fluid from the intestinal wall into the lumen of the intestine, giving rise to diarrhea. Which of the following proteins is likely inhibited or compromised in function to produce this ethanol-induced diarrhea?
Claudins
In mammalian embryos such as the mouse, the fertilized egg divides three times to form eight loosely packed cells, which become tightly adherent in a process known as compaction. In the late 1970s, several laboratories made antibodies against mouse cell surface proteins. The antibodies prevented compaction, as did removal of Ca2+ from the medium. What sort of protein do the antibodies probably recognize, and why?
Compaction is probably mediated by cadherins, because the proteins involved appear to be calcium-sensitive cell surface proteins.
It is now possible, using nanoengineering techniques, to attach magnetic beads to the surface of large cells to measure how mechanically stiff they are. It is also known that acrylamide, which is polymerized to make gels for protein electrophoresis, is very toxic. One effect of acrylamide is to depolymerize intermediate filaments, such as keratin. What effect would you predict acrylamide treatment would have on the mechanical rigidity of a keratinocyte (skin cell)? Explain your answer.
Disrupting intermediate filaments will result in cells that are more susceptible to mechanical forces. In the case of the keratinocytes, disrupting keratin, a key IF in these cells, would result in very fragile cells. Less force would need to be applied using the magnetic beads to damage them or change their shape.
Cultured fibroblast cells will secrete collagen and produce connective tissue fibers after the addition of material from a culture of lung macrophages that have been exposed to silica particles. What does this tell you about the deposition of collagen nodules in the lungs of silicosis patients?
Exposure of silica particles apparently causes the macrophages to release a soluble factor that stimulates fibroblast cells in the lung to deposit collagen fibers, probably in an attempt to seal off the silica in the lung.
What hypothesis was being tested with the Δformin strain?
Formin is required for the signal transduction pathway leading to shmoo formation.
Collagens are NOT __________.
Found as bundles of double-helical polypeptides
A model helps scientists form testable hypotheses. What hypothesis was being tested with the ΔFus3 strain?
Fus3 is required for the signal transduction pathway leading to shmoo formation.
What causes catastrophe of the microtubule in vitro?
GTP hydrolysis
What is the role of GTP in microtubule polymerization?
GTP stabilizes the tip of the microtubule, allowing more monomers to be added.
If a researcher wanted to design a drug to inhibit the nucleation of new microtubules at the centrosome, which molecular target should she focus on?
Gamma-tubulin
_____ aid in the coordination of the activities of adjacent animal cells.
Gap (communicating) junctions
Describe the synthesis and glycosylation of glycoproteins of the plasma membrane. Drag the terms on the left to the appropriate blanks on the right to complete the sentences.
Integral membrane proteins are synthesized on the rough ER, with oligosaccharide side chains added in part on the lumenal side of the rough ER (core glycosylation) and in part on the lumenal side of the Golgi complex (terminal glycosylation). Side chains therefore face the interior of both organelles as well as the interior of transport vesicles and become oriented toward the exterior of the cell when the vesicles fuse with the plasma membrane.
Which of these statements is NOT true of actin?
It varies considerably from organism to organism.
Which of these statements accurately describes an MTOC?
MTOCs bind and stabilize the minus ends of microtubules.
What assumption did you make about biological membranes in order to answer the question in Part B?
Membrane asymmetry is maintained throughout the rough ER, Golgi, and plasma membrane.
What do you predict would happen if the yeast had a mutation that prevented the G protein from binding GTP?
No shmoo would form in response to mating factor.
Explain why the carbohydrate groups of membrane glycoproteins are always found on the outer surface of the plasma membrane.
Outer monolayer originally faced the interior of the rough ER and Golgi, where the enzymes involved in glycosylation are located.
Proteins that are secreted from a eukaryotic cell must first travel through the endomembrane system. Drag the labels onto the diagram to identify the path a secretory protein follows from synthesis to secretion. Not all labels will be used
Protein synthesis > endoplasmic reticulum > cis Golgi cisternae > medial Golgi cisternae > trans Golgi cisternae > plasma membrane > Extracellular space
How would the drug taxol affect the in vitro dynamic instability and treadmilling experiments?
Taxol would stabilize the microtubules in both experiments, leading to polymerization without catastrophe.
How do you think the fibers get into the lysosomes?
The fibers or particles are probably taken up by endocytosis, followed by transport via early and late endosomes to a heterophagic lysosome.
What effect do you think fiber or particle accumulation has on the lysosomes?
The fibers or particles may physically abrade the lysosomal membrane, causing it to become leaky.
What do you think happens to the silica particles or asbestos fibers when such cells die?
The fibers or particles released on cell death presumably are available for ingestion by macrophages, with the same end result.
The movement of kinesin along the microtubule has been described similarly to how a human walks. One foot must be planted on the microtubule while the other releases the microtubule to move forward. Which of the following must be true if kinesin is to walk along the microtubule without falling off?
The foot on the microtubule must have a high affinity, and the foot moving forward must have a low affinity.
What would happen in the treadmilling experiment if a non-hydrolyzable analogue of GTP were used?
The microtubule would treadmill until the new tubulin, with non-hydrolyzable GTP, reached the minus end, and then it would only extend at the plus end.
In skeletal muscle sarcomeres, the H zone is in the middle and bounded on each side by a Z line. During contraction, the Z lines on either side move in opposite directions toward the H zone. Myosin, however, can crawl along an actin filament in only one direction. How can you reconcile movements of Z lines in opposite directions with the unidirectional movement of myosin along an actin filament?
The myosin thick filaments are assembled with the rodlike tail domain located at the center of the filament and the globular heads located at the ends of the filament pointing away from the center. Therefore, the globular myosin heads at each end of the thick filament have opposite polarities. This results in the movement of the actin filaments in opposite directions so that actin filaments from each Z line are drawn to the center of the sarcomere.
Fus3 kinase and formin proteins are generally distributed evenly throughout a yeast cell. Based on the model in the diagram, why does the shmoo projection emerge on the same side of the cell that bound the mating factor?
The only formin molecules that get phosphorylated and thus activated are those near the G protein-coupled receptor that binds mating factor.
What is the difference between the plus and minus ends of the microtubule in in vitro experiments?
The plus end has a lower critical concentration for tubulin heterodimers.
A patient was diagnosed to possess a mutation in an ER-resident protein in which the ER-signal sequences of the protein were inappropriately deleted and instead replaced with a mannose-6-phosphate during protein synthesis and posttranslational modification. What is the likely fate of this mutant protein?
The protein would be targeted to the lysosomes.
Which of the following accurately describes the nucleotide dependence of cilia and flagella structure and function?
The structures of cilia and flagella are dependent on GTP, whereas the functions of cilia and flagella are dependent on ATP.
Fluorescent dyes were used in the experiment to distinguish the old and new cell walls of the yeast cells. First, the existing cell walls of each strain were stained with a green fluorescent dye. These green-stained cells were then exposed to mating factor and then stained with a red fluorescent dye that only labels new cell wall growth. Growth of the cell on all sides (symmetric growth) is indicated by a uniform yellow color, resulting from merged green and red stains. This occurs normally in wild-type cells that have not been exposed to mating factor. When designing an experiment, scientists make predictions about what results will occur if their hypothesis is correct. One of their hypotheses was that Fus3 kinase is required for the signal transduction pathway leading to shmoo formation. If this hypothesis is correct, what result should be observed in the ΔFus3 strain?
The ΔFus3 strain should not form shmoos, and the cells should not have a red zone in their walls.
One of their hypotheses was that formin is required for the signal transduction pathway leading to shmoo formation. If this hypothesis is correct, what result should be observed in the Δformin strain?
The Δformin strain should not form shmoos, and the cells should not have a red zone in their walls.
Which of the following would result if an inhibitor of myosin light-chain kinase (MLCK) were added to a culture of smooth muscle cells?
There would be no muscle contraction.
Stress fibers of nonmuscle cells contain contractile bundles of actin and myosin II. For stress fibers to contract or develop tension, how would actin and myosin have to be oriented within the stress fibers?
There would have to be regions of antiparallel actin filaments (with some actin filaments attached to myosin in the opposite orientation).
Which of the following accurately depicts the roles of particular proteins in microfilament branching?
WASP proteins activate the Arp2/3 complex to promote microfilament branching.
Historically, an important strategy for disrupting the adhesion of integrins to their ligands is by using a synthetic peptide that mimics the binding site on the ECM molecule to which the integrin attaches. In the case of fibronectin, the amino acid sequence is arginine-glycine-aspartate (when written using the single letter designation for each amino acid, this sequence becomes RGD). Explain why addition of such synthetic peptides would disrupt binding of cells to their normal substratum.
When the integrins are bound to RGD peptides, their receptors will be unavailable for binding to FN (or LN), and thus cells will be inhibited from binding to the ECM.
The micrographs shown below were taken of wild-type, ΔFus3, and Δformin cells after they were stained green, exposed to mating factor, and then stained red. For each micrograph, drag the labels to answer the questions. Labels may be used once, more than once, or not at all.
Wild Type: Red Green - Asym - Y - Y - Y ΔFus3: Yellow - Sym - N - Y - Y Δformin: Yellow - Sym - N - Y - Y
The mannose-6-phosphate receptor would have what type of protein tag?
a trans-Golgi retention tag
Which of the following experimental treatments would NOT be a potentially effective strategy to inhibit or prevent cell-cell adhesion?
adding an antagonist to prevent integrin function
A novel enteropathogenic bacterium is discovered that is shown to bind to cadherin molecules in the guts of mammals. The result of this cadherin binding is a disruption of the actin cytoskeleton in the vicinity of binding. Which of the following intracellular molecules is likely disrupted by the binding of this enteropathogenic bacterium?
alpha/beta-catenins
Phalloidin is covalently attached to a fluorescent molecule and added to dividing, ciliated cells in culture. Which of the following accurately depicts where the fluorescence should be localized in the cells when looking at the treated cultures using fluorescence microscopy?
at the inner surface of the plasma membrane
In the Golgi complex, __________.
carbohydrate side chains of glycoproteins are modified
Sarin is a toxic substance that irreversibly inhibits the enzyme responsible for degrading acetylcholine (acetylcholinesterase). Which of the following reactions would you expect of an organism poisoned by sarin?
continuous muscle spasms and convulsions
The primary role of _____ is to bind animal cells together.
desmosomes
Which is the correct order of assembly of intermediate filaments?
dimer, tetramer, protofilament, intermediate filament
A researcher creates a mutant yeast cell line in which Rho GTPase-specific GAPs are more active than in wild-type yeast. Which of the following structures/processes would LEAST LIKELY be affected in this mutant?
formation of microtubule organizing centers
Which is the correct order from least to most complex?
glucuronate, hyaluronate, GAG chains, proteoglycans
Flow of vesicles from the ER to the Golgi involves all of these structures EXCEPT __________.
kinesin
For a cancerous tumor to move from tissue to tissue in metastasis, which proteins of the basal lamina must it be able to degrade or pass through?
laminins and type IV collagen
Maturation of a lysosome occurs when __________.
late endosomes acidify to activate the acid hydrolases
All proteins are synthesized by ribosomes in the cell. Some ribosomes float freely in the cytosol, while others are bound to the surface of the endoplasmic reticulum. Most proteins made by free ribosomes function in the cytosol. Proteins made by bound ribosomes either function within the endomembrane system or pass through it and are secreted from the cell. Which of the following proteins are synthesized by bound ribosomes?
lysosomal enzyme Insulin ER protein
A researcher extracts the cytosol and cytoskeletal components from the cell and places the mixture into a tube. What result do you expect if the researcher adds a nonhydrolyzable GTP analog to the mixture in vitro?
overstabilization of all polymerized microtubules present in the tube
Which of the following answers correctly completes this statement? __________ in plant cell walls and __________ in extracellular matrices both/all perform the function of __________.
pectins; fibronectins and laminae; adhesive molecules
What types of substances would move retrograde to the rough ER?
proteins with a KDEL retrieval tag
What process involves proteins in vesicles being held at the plasma membrane until the cell is signaled to release them?
regulated secretion
Anterograde movement of transition vesicles is from __________.
the rough ER to the cis Golgi
Which of these cell junctions form a barrier to the passage of materials?
tight junctions
In addition to testing shmoo formation in the two mutant strains of yeast, the scientists also tested shmoo formation in wild-type yeast. What is the purpose of including wild-type yeast cells in the experiment?
to show normal shmoo formation under the experimental conditions
