Question # 1 Select the single best answer to the numbered question.
Each of the following is true of both cadherins and integrins EXCEPT X
A.
both are transmembrane glycoproteins
X
B.
both can associate with the actin cytoskeleton
X
C.
both represent gene families
✓
D.
both may be found in zonula adherens junctions
X
E.
both are involved in cell adhesion
You answered: C X Explanations: A.
This is a true true statement and hence an incorrect answer for this EXCEPT question. question.
B.
This is a true true statement and hence an incorrect answer for this EXCEPT question. question. Integrins associate with the actin cytoskeleton at focal adhesions (sites of cell-ECM adhesion. Cadherins associate with the actin cytoskeleton in adherens junctions between e pithelial cells.
C.
This is a true statement statement and hence an incorrect incorrect answer for this EXCEPT EXCEPT question. question.
D.
Only cadherins are found in in zonula adherens adherens junctions. Hence this is an incorrect incorrect statement statement and the the CORRECT answer to this EXCEPT question.
E.
This is a true statement statement and hence an incorrect incorrect answer for this EXCEPT EXCEPT question. question. Cadherins are involved in in desmosomes and adherens junctions. Integrins are involved in focal adhesions a nd hemidesmosomes.
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Question # 2 Select the single best answer to the numbered question.
Which of the following BEST describes the adhesive interaction required for neutrophil (leukocyte) "rolling" as depicted in the sequence labeled "1" in the diagram?
X
A.
I-CAM molecules on the neutrophil cell surface bind to integrins on the endothelial cell surface
✓
B.
Selectins on the endothelial cell surface bind to specific carbohydrates carbohydrates on the neutrophil cell surface
X
C.
Integrins on the neutrophil cell surface bind to selectins on the endothelial cell surface
X
D.
Selectins on the neutrophil cell surface bind to specific carbohydrates on the endothelial cell surface
You answered: B ✓ Explanations: A.
Sequence 2 (not sequence sequence 1) in the diagram diagram is due to an an interaction of I-CAM on the endothelial surface (not the neutrophil surface) with an in tegrin on the neutrophil surface (not the endothelial cell surface). For these reasons, this is an incorrect answer.
B.
This is a correct correct description of the receptor interactions interactions responsible responsible for events shown in "1" in the diagram and hence the correct answer.
C.
Integrins do not bind to to selectins. The selectins selectins on the endothelial surface surface bind to carbohydrate groups groups on the neutrophil cell surface. Therefore, this is an incorrect answer.
D.
This is backwards backwards from what actually actually happens during the events shown shown in "1" in the diagram. The selectins selectins on the endothelial cell surface (not the neutrophil surface) interact with carbohydrate groups on the neutrophil surface (not the endothelial cell surface). Hence, this is a n incorrect answer.
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Question # 3 Select the single best answer to the numbered question. Cell adhesion to the extracellular matrix (ECM) glycoprotein fibronectin can involve A.
the binding of select immunoglobin superfamily members (IgSF) to the Arg -Gly-Asp (RGD) sequence in fibronectin.
X
B.
Ca independent binding of selectins to the Arg-Gly-Asp (RGD) sequence in fibronectin.
X
C.
Ca dependent binding of selectins to the Arg-Gly-Asp (RGD) sequence in fibronectin.
✓
D.
the binding of integrins to the Arg-Gly-Asp (RGD) sequence in fibronectin.
X
E.
Ca dependent binding of selectins to specific carbohydrate groups on the fibronectin glycoprotein.
X
+ +
+
You answered: D ✓ Explanations: A.
IgSF molecules are involved in cell-cell adhesion and do do not bind ECM molecules. Thus, this is an incorrect answer. +
B.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not bind to fibronectin. Thus, this is an incorrect answer.
C.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not bind to fibronectin. Thus, this is an incorrect answer.
D.
The RGD amino acid sequence in fibronectin, and other proteins such such as fibrinogen, is the primary cell cell adhesion site recognized by select integrins at the cell surface. surface. Thus, this is the correct answer.
E.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not mediate the adhesion of cells to the fibronectin glycoprotein. glycoprotein. Thus, this is an incorrect answer.
+
+
This question is not currently linked to the learning objective database. Question problem?
You answered: B ✓ Explanations: A.
Sequence 2 (not sequence sequence 1) in the diagram diagram is due to an an interaction of I-CAM on the endothelial surface (not the neutrophil surface) with an in tegrin on the neutrophil surface (not the endothelial cell surface). For these reasons, this is an incorrect answer.
B.
This is a correct correct description of the receptor interactions interactions responsible responsible for events shown in "1" in the diagram and hence the correct answer.
C.
Integrins do not bind to to selectins. The selectins selectins on the endothelial surface surface bind to carbohydrate groups groups on the neutrophil cell surface. Therefore, this is an incorrect answer.
D.
This is backwards backwards from what actually actually happens during the events shown shown in "1" in the diagram. The selectins selectins on the endothelial cell surface (not the neutrophil surface) interact with carbohydrate groups on the neutrophil surface (not the endothelial cell surface). Hence, this is a n incorrect answer.
This question is not currently linked to the learning objective database. Question problem?
Question # 3 Select the single best answer to the numbered question. Cell adhesion to the extracellular matrix (ECM) glycoprotein fibronectin can involve A.
the binding of select immunoglobin superfamily members (IgSF) to the Arg -Gly-Asp (RGD) sequence in fibronectin.
X
B.
Ca independent binding of selectins to the Arg-Gly-Asp (RGD) sequence in fibronectin.
X
C.
Ca dependent binding of selectins to the Arg-Gly-Asp (RGD) sequence in fibronectin.
✓
D.
the binding of integrins to the Arg-Gly-Asp (RGD) sequence in fibronectin.
X
E.
Ca dependent binding of selectins to specific carbohydrate groups on the fibronectin glycoprotein.
X
+ +
+
You answered: D ✓ Explanations: A.
IgSF molecules are involved in cell-cell adhesion and do do not bind ECM molecules. Thus, this is an incorrect answer. +
B.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not bind to fibronectin. Thus, this is an incorrect answer.
C.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not bind to fibronectin. Thus, this is an incorrect answer.
D.
The RGD amino acid sequence in fibronectin, and other proteins such such as fibrinogen, is the primary cell cell adhesion site recognized by select integrins at the cell surface. surface. Thus, this is the correct answer.
E.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not mediate the adhesion of cells to the fibronectin glycoprotein. glycoprotein. Thus, this is an incorrect answer.
+
+
This question is not currently linked to the learning objective database. Question problem?
Question # 4 Select the single best answer to the numbered question.
Cell adhesion to the extracellular matrix (ECM) glycoprotein fibronectin can involve which of the following scenarios? A.
The binding of select immunoglobin superfamily members (IgSF) to the Arg -Gly-Asp (RGD) sequence in fibronectin
X
B.
Ca independent binding of selectins to the Arg-Gly-Asp (RGD) sequence in fibronectin
X
C.
Ca dependent binding of selectins to the Arg-Gly-Asp (RGD) sequence in fibronectin
✓
D.
The binding of integrins to the Arg-Gly-Asp (RGD) sequence in fibronectin
X
E.
Ca dependent binding of selectins to specific carbohydrate groups on the fibronectin glycoprotein
X
+ +
+
You answered: D ✓ Explanations: A.
IgSF molecules are involved in cell-cell adhesion and do do not bind ECM molecules. Thus, this is an incorrect answer. +
B.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not bind to fibronectin. Thus, this is an incorrect answer.
C.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not bind to fibronectin. Thus, this is an incorrect answer.
D.
The RGD amino acid sequence in fibronectin, and other proteins such such as fibrinogen, is the primary cell cell adhesion site recognized by select integrins at the cell surface. surface. Thus, this is the correct answer.
E.
Selectins contain Ca -dependent lectin domains that bind to specific carbohydrates expressed at the surfaces of other cells in order to mediate cell-cell adhesive interactions. Selectins do not mediate the adhesion of cells to the fibronectin glycoprotein. glycoprotein. Thus, this is an incorrect answer.
+
+
The question is mapped to following learning objectives for school year 2013-2014: 1.
(ID: 19833) Explain Explain the functional importance importance of the Arg-Gly-Asp (RGD) site in fibronectin and fibrinogen.
Question problem?
Question # 5 Select the single best answer to the numbered question.
Which of the following statements about desmosomes is true? X
A.
They are the portion of the junctional complex that is closest to the lumen
X
B.
They encircle the entire cell forming an adhesion belt
X
C.
They function as a diffusion barrier
✓
D.
They are associated with intermediate filaments
X
E.
Connexin membrane proteins contribute to their structure
You answered: D ✓ Default Explanation:
No explanation provided. This question is not currently linked to the learning objective database. Question problem?
Question # 6 Select the single best answer to the numbered question.
What is a characteristic of Glanzmann's Thrombasthenia? X
A.
It is caused by mutations in selectin genes
X
B.
There is an absence of pus following bacterial infection
✓
C.
Platelet aggregation is defective
X
D.
Platelet cadherins fail to bind to the actin cytoskeleton upon activation
X
E.
"Activated" platelets bind fibrinogen
You answered: C ✓ Explanations: A.
Glanzmann’s Thrombasthenia is a bleeding disorder involving defects in platelet aggregation. Selectins are not involved in platelet aggregation aggregation upon platelet activation. activation. Thus, this is an incorrect answer.
B.
Absence of pus (which is mostly mostly composed composed of neutrophils) indicates indicates la ikely ikely deficiency in leukocyte leukocyte function function as, for example, in the case of leukocyte adhesion deficiency (LAD). Glanzmann’s is a bleeding disorder involving defects in platelets, not leukocytes. Thus, this answer is not correct.
C.
This answer is correct because f ailure ailure of platelet aggregation is a feature of Glanzmann’s Thrombasthenia. The inability of platelets to bind fibrinogen, become activated and to aggregate is due to defects in platelet integrins.
D.
Cadherins are not not involved in platelet aggregation and, therefore, cannot account for the defects defects in platelet adhesion observed in Glanzmann’s patients. Thus, this is an incorrect answer.
E.
Normal activated platelets bind fibrinogen but those obtained from Glanzmann’s patients have defective integrins and do not bind fibrinogen. Fibrinogen binding is required for platelet aggregation. Thus, this answer is incorrect.
The question is mapped to following learning objectives for school year 2013 -2014: 1.
(ID: 19834) Describe the role of integrin αIIb/β3 receptor in normal platelet aggregation and the defects underlying Glanzmann’s Thrombasthenia.
Question problem?
Question # 7 Select the single best answer to the numbered question. Each of the following is true of both cadherins and integrins EXCEPT
X
A.
X
B.
both can associate with the actin cytoskeleton
X
C.
both represent gene families
X
D.
both may associate with intermediate filaments
✓
E.
both are involved in cell-extracellular matrix (cell-ECM) adhesion
both are transmembrane glycoproteins
You answered: E ✓ Explanations: A.
This is a true statement thus an incorrect answer for this EXCEPT question. Integrins function as heterodimers of distinct protein subunits, both of which are transmembrane glycoproteins. Cadherins are also transmembrane glycoproteins.
B.
This is a true statement thus an incorrect answer for this EXCEPT question. Integrins associate with the actin cytoskeleton at focal adhesions (sites of cell-ECM adhesion) on migrating. Cadherins also associate with actin cytoskeleton at the class of cell-cell adhesive contacts that includes adherens junctions (found in some epithelia and in cardiac muscle).
C.
This is a true statement thus an incorrect answer for this EXCEPT question. There are multiple cadherin and integrin genes expressed by cells and tissues throughout the body.
D.
This is a true statement thus an incorrect answer for this EXCEPT question. Intermediate filaments are associated with integrins in hemidesmosomes and with cadherins in desmosomes. Note that this does not contradict the statement in answer B.
E.
Cadherins are not involved in cell-ECM adhesion ; they are always involved in cell-cell adhesion. Integrins are involved in cell-ECM adhesion and in some cases, can mediate cell-cell adhesion. Because cadherins are not involved in cell-ECM adhesion this statement is incorrect, thus is the CORRECT answer for this EXCEPT question.
This question is not currently linked to the learning objective database. Question problem?
Your Score: 86 %
32) A type of adhesive junction that is associated with the connection between an epithelial cell and the basal lamella is the A) hemidesmosome. B) desmosome. C) gap junction. D) plasmodesmata. E) focal contact.
34) In the extracellular matrix of animal cells, collagen and elastin fibers are embedded with this matrix. A) glycoaminoglycans B) proteoglycans C) pectins D) lignins
E) both choices A and B 36) The organ where you would most likely expect to find actin microfilaments continuous with adherens junctions is the A) liver. B) stomach. C) kidney. D) brain. E) heart. 1) A person is genotypically blood type A. However, this individual also does not produce the lipid to which N-acetylgalactosamine is added, so the lipid is therefore not expressed on the surface of erythrocytes. This situation is known as the Bombay phenotype. When tested, this person will appear to be blood type A) A. B) B. C) AB. D) O. 2) Polarized cells are characterized by A) random orientation within a tissue. B) a polar flagellum. C) random orientation within an organ. D) distinct apical and basolateral sides. E) both choices B and D 3) Which of the following cell junctions are associated with the proper alignment of intestinal epithelial cells? A) gap junctions B) adhesive junctions C) tight junctions D) desmosomes E) all of the above 4) In animal cells, the extracellular matrix plays important roles in all of the following processes except A) cell division. B) motility. C) DNA replication. D) differentiation. E) adhesion. 5) A newly defined autoimmune disorder has resulted in an immune response against Type V collagen fibers. As a result, the most likely organ to be targeted in this response would be the A) skin. B) heart. C) lungs.
D) stomach. E) tongue. 6) Which of the following statements is true regarding cell-cell adhesion? A) Adhesion is coordinated with many cellular processes except cell survival. B) Adhesion molecules include plakoglobulin, which cements two cells together. C) Adherens junctions are exclusive to plant cells. D) Adhesive junctions are characterized by the attachment of long molecules of hyaluronate. E) Adhesive junctions are dynamic in response to cellular signals. 7) Which of the following is not associated with adhesive junctions? A) desmosomes B) hemidesmosomes C) plaques D) connexin E) cadherins 8) Which of the following is mismatched? A) IgSF[emdash]chondroitin B) cadherins?calcium ions C) selectins?leukocytes D) cadherins?embryonic development E) lectins?carbohydrates 9) Which of the following is false with regard to the extracellular matrix? A) These structures are external to the cell membrane, but are still an integral component of cell function. B) Extracellular matrices are only found in association with eukaryotic cells. C) Extracellular matrices play a role in determining the shape of a cell. D) Bone and cartilage are examples of cells that have specialized extracellular matrices associated with their function. E) Extracellular matrices play a role in determining the mechanical properties of tissues and organs. 10) Which of the following activities is not associated with cadherins? A) segregation of cells to specific tissues B) paracellular transport C) embryonic development D) establishment of synaptic connections E) loss of activity associated with cancer 11) Which of the following components is not associated with the primary cell wall? A) cellulose microfibrils B) hemicelluloses C) pectins D) glycoproteins E) lignins
12) Which of the following is the correct order for the synthesis of the plant cell wall, from the outermost layer to the innermost layer?
A) middle lamella; primary cell wall; secondary cell wall; plasma membrane B) primary cell wall; middle lamella; secondary cell wall; plasma membrane C) plasma membrane; secondary cell wall; primary cell wall; middle lamella D) middle lamella; secondary cell wall; primary cell wall; middle lamella E) primary cell wall; secondary cell wall; plasma membrane; middle lamella 13) You discover a dog suffering from a strange disorder that is due to an autoimmune response against its own cells. Upon further investigation, you find that the cells of various tissues are loosely arranged and do not have characteristic shapes and that the animal is prone to hemorrhage as the result of poor blood clotting. Based on these results, the target of the autoimmune response could be A) fibronectins. B) laminins. C) extensins. D) pectins. E) desmotubules. 14) The function of integrin-linked kinase during integrin-based signaling is A) integrin activation. B) anchorage-dependent growth. C) scaffolding protein. D) cell movement. E) anchorage-independent growth. 15) A patient is rushed to the emergency room and immediately needs a blood transfusion. The patient is found to have only anti-A antibodies in circulation. The blood type of this individual must be A) A. B) B. C) AB. D) O. 16) A person with neither anti-A nor anti-B antibodies in circulation has which of blood type? A) A B) B C) AB D) O 17) In which of the following organs would you expect to find adhesive junctions in humans? A) heart muscle B) skin epithelium C) uterus D) both choices A and B E) choices A, B, and C 18) Which of the following is correctly paired with regard to similarity in function? A) adhesive junctions-tight junctions B) desmotubule-gap junction C) tight junctions-gap junctions D) plaques-plasmodesmata E) connexons-desmosomes
19) Paracellular transport is associated with which of the following? A) adherens junctions B) integrins C) desmosomes D) tight junctions E) hemidesmosomes 20) You are investigating a clinical disorder in one of your patients. You discover that the patient has an autoimmune disease that targets and destroys fibroblasts. This disorder would most likel y affect A) fiber production by the cells, as occurs with blood clotting. B) annulus formation. C) hyluronate production in the joints. D) collagen production. E) all of the above 21) Of the proteoglycans associated with the extracellular m atrix in vertebrates, which of the following is associated with the lubrication of joints? A) chondroitin sulfate B) glucuronate C) hyaluronate D) keratan sulfate E) mucoproteins 22) The protein invasin is associated with A) Yersinia psuedotuberculosis. B) the construction of an integrin network in bacteria. C) plasmodemata. D) tight-junction ridge formation. E) lubrication of joints. 23) You are investigating cell localization by targeting the carbohydrates associated with various ce ll types. Based on this molecule's ability to bind various carbohydrates, which of the following would help determine which carbohydrates are found on the cell surface? A) cadherins B) proteoglycans C) pectins D) connexins E) lectins 24) Which of the following is mismatched with regard to similar excellular structures in plant and animal cells? A) elastins-extensins B) extracellular matrix-cell wall C) collagens-cellulose D) proteoglycans-hemicelluloses E) fibronectins-pectins 25) Some observations have suggested to researchers that substances associated with the extracellular
matrix may be involved in cell migration. This has been observed with the cell marker CD44 on the surface of cancer cells and their ability to be separate from one another and to easily metastasize to other regions of the body. This is most likely due to the interaction of CD44 and A) chondrotin sulfate. B) ICAMs. C) hyaluronate. D) fibronectins. E) elastin. 26) Which of the following is not associated with the basal lamina? A) serves as a structural support B) allows for movement of some small molecules C) can influence cell migrations in certain areas of the body D) contains collagen type IV, proteoglycans, laminins, and entactin E) contains the most abundant supply of fibronectins. 27) An elderly patient presents with blistering of the skin. You suspect an autoimmune disorder. If your suspicions are correct, the patient's serum should contain antibodies reactive to A) talin. B) vinculin. C) a-actinin. D) BPAG. E) actin. 28) In performing research, you treat frog zygotes with antibodies that bind E-cadherin. As a result, you expect A) the cells to become exclusively muscle tissue. B) the cells to be loosely associated and abort development. C) the cells to be loosely associated and develop into a novel strain of frog. D) the cells to divide uncontrollably. E) no change with regard to development.
29) Collagens are associated with which of the following types of cellular junctions? A) gap junctions B) tight junctions C) plasmodesmata D) adhesive junctions E) none of the above 30) Focal contact is associated with which of the following type of cellular junction? A) adhesive junction B) gap junction C) plasmodesmata D) tight junctions E) all of the above 31) The type of cellular junction prominent in the stomach and kidney is the A) plasmodesmata.
B) gap junction. C) adhesive junction. D) tight junction. E) laminin junction. 32) A type of adhesive junction that is associated with the connection between an epithelial cell and the basal lamella is the A) hemidesmosome. B) desmosome. C) gap junction. D) plasmodesmata. E) focal contact. 33) The insoluble layer of aromatic alcohols that are primarily found in woody tissues are the A) annulus. B) cadherins. C) proteoglycans. D) lignins. E) pectins. 34) In the extracellular matrix of animal cells, collagen and elastin fibers are embedded with this matrix. A) glycoaminoglycans B) proteoglycans C) pectins D) lignins E) both choices A and B 35) The molecule of the extracellular matrix of animal cells that is associated with joint lubrication and friction reduction is A) glycosaminoglycan. B) proteoglycan. C) hyaluronate. D) pectin. E) fibronectin. 36) The organ where you would most likely expect to find actin microfilaments continuous with adherens junctions is the A) liver. B) stomach. C) kidney. D) brain. E) heart. 37) The plant cell wall network is comprised of all of the following except A) hyaluronate. B) cellulose. C) extensin. D) hemicellulose. E) pectin.
38) The primary polysaccharides associated with the plant cell wall are the A) hemicelluloses. B) extensins. C) fibronectins. D) pectins. E) both choices A and D 39) A collection of fibrous intracellular attachment proteins is called a(n) A) annulus. B) connexon. C) plaque. D) tonofilament. E) both choices C and D 40) The autoimmune response to desmosomes or desmosomal components (not hemidesmosomes) leads to a blistering skin disease known as A) pemphigus. B) Ehlers?Danos syndrome. C) syndecan. D) junctional epidermolysis bullosa. E)lis tero sistr iosis 1). Which of the following techniques has recently aided the study of receptor proteins? . a). protein purification b). monoclonal antibodies c). isolation of cell signal molecules d). all of these Answer:b 2). Which of the following describes autocrine signaling? a). Signal molecules released by cells diffuse through the extracellular fluid to other cells. b). Signal molecules enter the organism's circulatory system and travel throughout the body. c). Signal molecules are released from a cell and bind to receptors on its own plasma membrane. d). Signal molecules are released into a narrow space between cells called a synapse. Answer:c 3). Intracellular receptors usually bind a). water-soluble signals. b). large molecules that act as signals. c). signals on the cell surface. d). lipid-soluble signals. Answer:d 4). Which of the following is not a type of cell surface receptor? a). chemically gated ion channels b). intracellular receptors c). enzymic receptors d). G-protein-linked receptors Answer:b
5). Which of the following is not a second messenger? a). adenylyl cyclase b). cyclic adenosine monophosphate c). calcium ions d). cAMP Answer:a 6). The amplification of a cellular signal requires all but which of the following? a). a second messenger b). DNA c). a signal molecule d). a cascade of protein kinases Answer:b 7). MHC proteins are a). molecules that determine a person's blood type. b). large molecules that pass through the membrane many times. c). identity markers present on the surface of an individual's cells. d). different for each type of tissue in the body. Answer:c 8). Sheets of cells are formed from which type of cell junctions? a). tight junctions b). anchoring junctions c). communication junctions d). none of these Answer:a 9). Cadherin can be found in which of the following? a). tight junctions b). anchoring junctions c). communication junctions d). adherens junctions Answer:b 10). Plasmodesmata are a type of a). gap junction. b). anchoring junction. c). communicating junction. d). tight junction. Answer:c
Test Your Visual Understanding 1). Match the following l abels with the appropriate structures in the figure, and explain where each type of junction is found. adherens junction desmosome gap junction hemidesmosome tight junction Answer: 1). Tight junction with #1, Adherens junction with #2, Desmosomes with #3, Gap junction with #4 and Hemidesmosome with #5 1--Tight junction Tight junctions hold cells together in a sheet, restricting the movement of substances between the cells. Tight junctions are found in cells that line the digestive tract.
2--Adherens junction Adherens junctions are anchoring junctions that use integrin to hold cells together by anchoring to the cells' actin networks. Adherens junctions, as other anchoring junctions are found in tissues that are subject to mechanical stress such as muscle and epithelium. 3--Desmosomes Desmosomes are anchoring junctions that use cadherin to hold cells together by anchoring to the cells' actin networks, or for more stable cell-to-cell connections by anchoring to the cells' intermediate fibers. Desmosomes, as other anchoring junctions are found in tissues that are subject to mechanical stress such as muscle and epithelium. 4--Gap junction Gap junctions are communicating junctions that use protein channels called connexons to create passageways between cells. When the connexons of two adjacent cells are lined up, a direct connection between the cytoplasms of the two cells is made. Small molecules and ions can pass freely between the cells. Gap junctions are found in animal cells. 5--Hemidesmosome Hemidesmosomes are anchoring junctions that use cadherin to hold cells to an extracellular matrix. Hemidesmosomes are found in epithelial cells, holding them to a basement membrane.
Apply Your Knowledge 1). In paracrine signaling, the signal molecule is destroyed by enzymes in 6 milliseconds. The diffusion rate of the signal through the extracellular fluid is 2 nanometer/1 millisecond. How long will the signal last in the extracellular fluid, and what is the farthest distance a target cell can be from the releasing cell to be affected by the signal? Answer: Enzymes breakdown the signal molecule in 6 milliseconds so the signal can only last for 6 milliseconds in the extracellular fluid. Therefore, the signal has only 6 mil liseconds to travel to its target cell. If the signal can travel 2 nanometers/millisecond then: 2 nanometers x 6 milliseconds = 12 nanometers The farthest distance a target cell can be from the releasing cell is 12 nanometers. 2). At first glance, the signaling systems that involve cell surface receptors may appear rather complex and indirect, with their use of G proteins, second messengers, and often multiple stages of enzymes. What are the advantages of such seemingly complex response systems? Answer: There are several advantages to response system that is organized in multiple levels. The first is obviously the ability to amplify the signal. With the multiple stages of enzymes, a small amount of a signal is all that is needed to get the response going. This allows for a very high level of sensitivity. Another advantage is the ability of the cell to use the same "machinery" for different signals--not having to produce new cascade machines to elicit t he same response or a related response. If two signals produce the same response, two different G proteins could activate the same adenylyl cyclase and activate the same cascade. Similarly, the same second messenger, for example cAMP could be used in different cascade responses, offering a certain redundancy to the system. 3). Shigella flexneri is one of several species of bacteria that cause shigellosis, or bacillary dysentery. Recent evidence has shown that S. flexneri cannot spread between the epithelial cells of the intestines without the expression of cadherin by those cells. Why do you suppose it cannot? Answer: Shigella flexneri invades one cell, multiplies and then spreads to contiguous epithelial cells. Cells that are expressing cadherin are closely adhering to t heir neighboring cells, which makes it easier for Shigella flexneri to spread.
1. Which of the following type of organism is always multicellular? A. animals only B. plants only C. archae only D. prokaryotes only E. both animals and plants
Bloom's Level: Remember Section: 10.01 Topic: Cells
2. Which of the following is most TRUE about multicellular organisms when compared with unicellular organisms? A. Multicellular organisms carry out specialized functions, while unicellular organisms do not. B. Multicellular organisms can reproduce themselves, while unicellular organisms cannot. C. Multicellular organisms can digest more complex molecules than unicellular organisms. D. Multicellular organisms tend to have larger genomes than unicellular organisms. E. Multicellular organisms show development while unicellular organisms do not.
Bloom's Level: Understand Section: 10.01 Topic: Cells
3. The bones and cartilage in animals serve the same function as ________ in plants? A. leaves B. phloem C. capillaries D. wood E. xylem
Bloom's Level: Understand Section: 10.01 Topic: Cells
4. In animals, which of the following structures is largely composed of extracellular matrix? A. kidney B. intestine C. eye D. cartilage E. muscle
Bloom's Level: Remember Section: 10.01 Topic: Cells
5. Which of the following is NOT a function of the extracellular matrix? A. provides strength B. provides structural support C. provides organization of cells throughout the organism D. provides an important source of energy for the organism E. cell signaling
Bloom's Level: Remember Section: 10.01 Topic: Cells
6. Which of the following ECM molecules provides tensile strength? A. fibronectin B. collagen C. laminin D. elastin E. proteoglycan
Bloom's Level: Remember Section: 10.01 Topic: Cells
7. Which of the following statements about the ECM is most CORRECT? A. It is composed of living cells. B. Its components are produced by specialized cells and transported throughout the body and deposited around the cell. C. It is a source of protein for cells. D. It protects cells from infectious agents. E. Its components are produced and secreted by the cell.
Bloom's Level: Understand Section: 10.01 Topic: Cells
8. The major macromolecules of the ECM are polysaccharides and A. lipids. B. fat. C. proteins. D. nucleotides. E. amino acids.
Bloom's Level: Remember Section: 10.01 Topic: Cells
9. Which of the following statements about collagen is INCORRECT? A. There can be numerous types of collagen in multicellular organisms B. It is produced from polymers of amino acids. C. It tends to promote the "sticky" characteristics of the ECM. D. Its breakdown is a contributing characteristic of wrinkling during aging. E. It is a major component of the ECM for cartilage and bone.
Bloom's Level: Understand Section: 10.01 Topic: Cells
10. Which collagen type is most rigid and is very abundant in bones and tendons? A. Type I B. Type II C. Type III D. Type IV E. Type V
Bloom's Level: Remember Section: 10.01 Topic: Cells
11. Which ECM molecule provides structure while allowing certain tissues to expand and contract (e.g., lungs during breathing, intestine during digestion)? A. collagen B. elastin C. fibronectin D. laminin E. glycosaminoglycans
Bloom's Level: Apply Section: 10.01 Topic: Cells
12. This polysaccharide is an important ECM component for the exoskeleton of many insects and shellfish. A. proteoglycan B. glycosaminoglycans C. collagen D. chitin E. laminin
Bloom's Level: Remember Section: 10.01 Topic: Cells
13. Which of the following statements about proteoglycans is TRUE? A. Proteoglycans are composed of collagen. B. Proteoglycans are composed of polysaccharides called glycosaminoglycans. C. Proteoglycans provide resistance to compression. D. Proteoglycans are both composed of collagen and provide resistance to compression. E. Proteoglycans are both composed of polysaccharides called glycosaminoglycans and provide resistance to compression.
Bloom's Level: Understand Section: 10.01 Topic: Cells
14. Which of the following ECM molecules is probably the most abundant organic molecule on Earth? A. proteoglycans B. collagen C. chitin D. cellulose E. laminins
Bloom's Level: Understand Section: 10.01 Topic: Cells
15. Which of the following statements about the cell wall is FALSE? A. The cell wall constitutes the ECM of plants. B. The cell wall is composed predominantly of proteins. C. The cell wall provides protection, rigidity, and shape to plant cells. D. The cell wall is composed of two distinct layers. E. The cell wall is composed mainly of carbohydrates.
Bloom's Level: Remember Section: 10.01 Topic: Cells
16. All of the following statements about cellulose are true EXCEPT: A. Cellulose is composed of fibers of carbohydrates. B. Cellulose is an important source of plant fiber for our diet. C. Cellulose is the primary molecule found in wood. D. Cellulose is one of the most abundant organic molecules on Earth. E. Certain animals like ourselves can easily digest cellulose and use it as a source of energy.
Bloom's Level: Understand Section: 10.01 Topic: Cells
17. Which of the following forms a protective layer outside of the plasma membrane of the plant cell? A. cell wall B. cellulose C. chitin D. pectin E. proteoglycans
Bloom's Level: Remember Figure: 10.05 Section: 10.01 Topic: Cells
18. Which of the following is NOT a function of cellular junctions? A. Cellular junctions hold adjacent cells together. B. Cellular junctions prevent leakage of materials between cell layers. C. Cellular junctions permit the direct exchange of small molecules between cytosol of adjacent cells. D. Cellular junctions bond cells to their ECM. E. Cellular junctions promote the motility of adjacent cells.
Bloom's Level: Remember Section: 10.02 Topic: Cells
19. All of the following represent anchoring junctions EXCEPT A. tight junctions. B. focal adhesions. C. hemidesmosomes. D. desmosomes. E. adherens junctions.
Bloom's Level: Remember Figure: 10.07 Section: 10.02 Topic: Cells
20. These act as rivets anchoring adjacent cells together at spots throughout the cell. A. adherens junctions B. desmosomes C. hemidesmosomes D. focal adhesions E. fibronectin
Bloom's Level: Remember Figure: 10.07 Section: 10.02 Topic: Cells
21. These anchorage junctions interact with intermediate filaments and anchor cells to the extracellular matrix. A. adherens junctions B. desmosomes C. hemidesmosomes D. focal adhesions E. fibronectin
Bloom's Level: Remember Figure: 10.07 Section: 10.02 Topic: Cells
22. Which of the following statements comparing hemidesmosomes with desmosomes is TRUE? A. Hemidesmosomes are anchorage junctions but desmosomes are not. B. Hemidesmosomes interact with actin filaments while desmosomes interact with intermediate filaments. C. Both hemidesmosomes and desmosomes associate with integrin, but not cadherin molecules. D. Hemidesmosomes anchor cells to the ECM while desmosomes anchor cells to other cells. E. Hemidesmosomes are found in plant cells while desmosomes are found in animal cells.
Bloom's Level: Understand Section: 10.02 Topic: Cells
23. Which of the following is NOT a component of focal adhesions? A. cadherins B. integrins C. actin filaments D. linker protein E. fibronectin/collagen
Bloom's Level: Remember Section: 10.02 Topic: Cells
24. All of the following are components of the adherens junction complex EXCEPT A. cadherins. B. Ca2+. C. intermediate filaments. D. linker protein. E. actin filaments.
Bloom's Level: Remember Section: 10.02 Topic: Cells
25. Which of the following cell junctions would function the LEAST like glue? A. gap junctions B. adherens junctions C. focal adhesions D. hemidesmosomes E. desmosomes
Bloom's Level: Understand Section: 10.02 Topic: Cells
26. This forms a seal that prevents the movement of substances between cells, for instance from the intestinal lumen into the blood. A. gap junctions B. tight junctions C. desmosomes D. hemidesmosomes E. focal adhesions
Bloom's Level: Remember Figure: 10.09 Section: 10.02 Topic: Cells
27. Gap junctions are to animal cells as ________ are to plant cells? A. middle lamella B. hemidesmosomes C. plasmodesmata D. primary cell walls E. tight junctions
Bloom's Level: Understand Figure: 10.11 Figure: 10.14 Section: 10.02 Topic: Cells
28. What structure cements plant cells together? A. middle lamella B. hemidesmosomes C. plasmodesmata D. primary cell walls E. adherens junctions
Bloom's Level: Remember Figure: 10.13 Section: 10.02 Topic: Cells
29. One can inject dyes of different sizes into a liver cell and determine those molecules that can readily pass through gap junctions. What sized molecules can pass through gap junctions? A. <1,000 Daltons B. >1,000 Daltons, but <1,500 Daltons C. >1,500 Daltons, but <5,000 Daltons D. >5,000 Daltons, but <10,000 Daltons E. >10,000 Daltons
Bloom's Level: Remember Section: 10.02 Topic: Cells
30. Which of the cell adhesion molecules is critical to transducing changes in the ECM to a change in the cell? A. connexins B. cadherins C. integrins D. fibronectins E. claudins
Bloom's Level: Remember Figure: 10.08 Section: 10.02 Topic: Cells
31. Which molecules are essential components of tight junctions? A. cadherins and connexins B. cadherins and integrins C. claudins and integrins D. cadherins and claudins E. connexins and claudins
Bloom's Level: Remember Section: 10.02 Topic: Cells
32. Which of the following junctions are important for cell signaling? A. adherins junctions B. gap junctions C. plasmodesmata D. desmosomes E. All of the choices are correct.
Bloom's Level: Understand Section: 10.02 Topic: Cells
33. A group of cells having similar structure and function is called a(n) A. tissue. B. organ. C. organ system. D. organism. E. population.
Bloom's Level: Remember Section: 10.03 Topic: Cells
34. The heart is a(n) ________ composed mainly of ________ tissue? A. tissue, cardiac B. organ, muscle C. tissue, connective D. organ, connective E. organ, epithelial
Bloom's Level: Understand Section: 10.03 Topic: Cells
35. Which of the following basic cell processes is NOT required for creating a tissue? A. cell division and differentiation B. cell connections C. cell morphology D. cell death E. cell migration
Bloom's Level: Remember Section: 10.03 Topic: Cells
36. This type of tissue is rich in extracellular matrix and includes tendon and cartilage. A. muscle B. connective C. epithelial D. nervous E. hepatic
Bloom's Level: Remember Section: 10.03 Topic: Cells
37. Which of the following tissue type covers or forms the lining of all internal and external body surfaces? A. muscle B. connective C. epithelial D. nervous E. hepatic
Bloom's Level: Remember Section: 10.03 Topic: Cells
38. The epithelial tissue of animal cells is most similar to the ________ of plant cells? A. xylem B. vascular C. dermal D. ground E. phloem
Bloom's Level: Understand Section: 10.03 Topic: Cells
39. Which type of tissue constitutes most of the wood of a tree trunk? A. dermal tissue B. parenchyma tissue C. collenchyma tissue D. sclerenchyma tissue E. vascular tissue
Bloom's Level: Apply Section: 10.03 Topic: Cells
40. Which of the following is TRUE of cork? A. It represents the major dermal tissue in bark. B. It helps transport nutrients and fluid. C. It serves a protective function D. It both represents the major dermal tissue in bark and helps transport nutrients and fluid. E. It both represents the major dermal tissue in bark and serves a protective function.
Bloom's Level: Understand Section: 10.03 Topic: Cells
True / False Questions
41. Cells can sense changes in the environment through alterations in the extracellular matrix. TRUE
Bloom's Level: Understand Section: 10.01 Topic: Cells
42. Wrinkling observed with aging is do to low production of the extracellular matrix molecule, fibronectin. FALSE
Bloom's Level: Remember Section: 10.01 Topic: Cells
43. Blood vessels that can expand and contract are largely composed of collagen as a structural extracellular matrix protein. FALSE
Bloom's Level: Remember Section: 10.01 Topic: Cells
44. Glycosaminoglycans and proteoglycans resist compression and are found in large abundance in joints of the body. TRUE
Bloom's Level: Remember Section: 10.01 Topic: Cells
45. Cellulose from the cell wall is a primary energy store for plants. FALSE
46. Rivets hold steel structures together much in the same way as tight junctions hold cells together. FALSE47. Integrin is a membrane protein that integrates changes in the ECM to alterations in movement or behavior of the cell. TRUE48. Unlike animals, plants lack a cell junction where small molecules can move from one cell to another cell. FALSE
49. The heart, skeletal muscles, and blood vessels all share a common feature in that they are composed of muscle tissue. TRUE
Bloom's Level: Understand Section: 10.03 Topic: Cells
50. The most prominent tissue type present in plants is the dermis. FALSE
Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because Athey always lead to the same cellular response. B.they amplify the original signal manyfold. Cthe number of molecules used is small and fixed. D.they are species specific. E.they counter the harmful effects of phosphatases. B Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane? A.. intracellular receptor B. G protein-coupled receptor C. receptor tyrosine kinase D. phosphorylated receptor tyrosine kinase dimer E. ligand-gated ion channel E The activation of receptor tyrosine kinases is characterized by A. GTP hydrolysis. B. channel protein shape change. C. dimerization and IP3 binding. D. dimerization and phosphorylation. E. a phosphorylation cascade. D
Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because A. only target cells retain the appropriate DNA segments. B. intracellular receptors are present only in target cells. C. only target cells possess the cytosolic enzymes that transduce the testosterone. D. only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor. E. most cells lack the Y chromosome required. B Consider this pathway: epinephrine- (G protein-coupled receptor)- protein adenylyl cyclase- cAMP. Identify the second messenger. A. adenylyl cyclase B. G protein-coupled receptor C. cAMP D. GTP E. G protein C Apoptosis involves all but which of the following? A. lysis of the cell B. digestion of cellular contents by scavenger cells C. cell-signaling pathways D. fragmentation of the DNA E. activation of cellular enzymes A Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells? A. Receptor studies indicated that epinephrine was a ligand. B. Glycogen breakdown was observed only when epinephrine was administered to intact cells. C. Enzymatic activity was proportional to the amount of calcium added to a cell-free extract. D. Epinephrine was known to have different effects on different types of cells. E. Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined. B Protein phosphorylation is commonly involved with all of the following except A. enzyme activation. B. activation of protein kinase molecules.
C. activation of G protein-coupled receptors. D. regulation of transcription by extracellular signaling molecules. E. activation of receptor tyrosine kinases. C Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways. A. Relay proteins are the "first messengers," the extracellular signaling molecules that bind to the membrane receptor. The signal transduction pathways are then formed by the second messengers, which are the relay molecules that respond to the first messengers. B. Signal transduction pathways are multistep pathways in which relay proteins and second messengers alternate. C. Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers. C Which statement correctly distinguishes the roles of protein kinases and protein phosphatases in signal transduction pathways? A. Protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. Protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases. B. Protein kinases are involved in signal transduction in unicellular eukaryotes such as yeast. Protein phosphatases are involved in signal transduction in multicellular eukaryotes. C. Protein kinases are more critical than protein phosphatases to signal transduction enzymes. A Cyclic GMP, or cGMP, acts as a signaling molecule whose effects include relaxation of smooth muscle cells in artery walls. In the penis, this signaling pathway and the resulting dilation of blood vessels leads to an erection. Select the correct statement about the effect of Viagra on this signaling pathway. A. Viagra increases the rate of hydrolysis of cGMP to GMP. B. Viagra inhibits the hydrolysis of GMP to GMP. C. Viagra prevents the formation of cGMP. B The cholera bacterium Vibrio cholerae produces an enzyme toxin that chemically modifies a G protein involved in
regulating salt and water secretion in intestinal cells. Stuck in its active form, the modified G protein stimulates the production of a high concentration of cAMP, which causes the intestinal cells to secrete large amounts of salts into the intestines, with water following by osmosis. An infected person quickly develops profuse diarrhea and if left untreated can soon die from the loss of water and salts. What is the basic effect of the cholera toxin? A.The basic effect of the cholera toxin is loss of specificity of the response of intestinal cells to a signaling molecule. B. The basic effect of the cholera toxin is premature termination of a signaling pathway. C. The basic effect of the cholera toxin is signal amplification. C Select all that apply.What are the functions of signal transduction pathways? A. Signal transduction pathways amplify the effect of a signal molecule. B. Signal transduction pathways allow different types of cells to respond differently to the same signal molecule. C. Signal transduction pathways convert a signal on a cell's surface to a specific cellular response. ABC Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because A. they counter the harmful effects of phosphatases. B. they amplify the original signal manyfold. C. they always lead to the same cellular response. D. they are species specific. E. the number of molecules used is small and fixed. B Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life? A. Receptor molecules have been identified in preparations of fossilized organisms billions of years old. B. Simple forms of life, such as prokaryotic cells, utilize cell signaling. C. The pathways in primitive organisms, such as bacteria, are short, whereas those in advanced forms, such as mammals, are long. D. Cell signaling is observed in organisms that do not utilize sexual reproduction. E. The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago. E
Which of the following is a substance that acts at a long distance from the site at which it is secreted? A. synaptic signal B. paracrine signal C. hormone D. neurotransmitter E. local regulator C What is most likely to happen to an animal's target cells that lack receptors for local regulators? A. Hormones would not be able to interact with target cells. B. They could divide but never reach full size. C. They might compensate by receiving nutrients via a factor. D. They could develop normally in response to neurotransmitters instead. E. They might not be able to multiply in response to growth factors from nearby cells. E Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding? A. endocrine signaling B. synaptic signaling C. autocrine signaling D. hormonal signaling E. paracrine signaling E In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function? A. digestion of unwanted parasite populations B. aggregation of bacteria that can cause cavities C. secretion of substances that inhibit foreign bacteria D. secretion of apoptotic signals E. formation of mating complexes B In which of the following ways do plant hormones differ from hormones in animals? A. Plant hormones interact primarily with intracellular receptors. B. Plant hormones may travel in air or through vascular systems. C. Animal hormones are primarily for mating and embryonic
development. D. Plant hormones are synthesized from two or more distinct molecules. E. Animal hormones are found in much greater concentration. B When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway? A. transducer B. endocrine molecule C. receptor D. signal molecule E. relay molecule D The following question is based on the figure below:Which of the following types of signaling is represented in the figure? A. synaptic B. hormonal C. paracrine D. autocrine E. long distance A The following question is based on the figure below:In the figure, the dots in the space between the two structures represent which of the following? A. hormones B. receptor molecules C. signal transducers D. pheromones E. neurotransmitters E In yeast signal transduction, a yeast cell A. produces signal molecules that change the cell itself, allowing it to interact with another cell. B. must physically and directly interact with another yeast cell. C. secretes molecules that result in responses by other yeast cells. D. produces response molecules that diffuse to other yeast cells. E. mates with another cell, after which the new cells secrete hybrid signals. C
To what does the term "ligand" refer in cell biology? A. the target cell of a signal molecule B. the change in shape that occurs when a signaling molecule binds to its receptor C. any small molecule that can bind in a specific manner to a larger one D. the bond that forms between a signaling molecule and its receptor E. a molecule that can occupy a receptor site while not activating the receptor C Dioxin, produced as a by-product of various industrial chemical processes, is suspected of contributing to the development of cancer and birth defects in animals and humans. It apparently acts by entering cells by simple diffusion and binding t o proteins in the cytoplasm, then altering the pattern of gene expression. Which of the following are likely to be the cytoplasmic proteins to which dioxin binds? A. growth factor receptors B. enhancers C. DNA polymerases D. nucleosomes E. transcription factors E What is the function of tyrosine-kinase receptors? A. enzymatic degrading of GTP to GDP B. enzymatic phosphorylation of tyrosine in the receptor protein C. enzymatic hydrolyzing of the signaling molecule shortly after its arrival D. allowing specific ions to enter the cell after ligand binding E. binding to nonpolar signaling molecules such as nitric oxide or the steroid hormones B Which of the following is true of transcription factors? A. They initiate the epinephrine response in animal cells. B. They transcribe ATP into cAMP. C. They regulate the synthesis of lipids in the cytoplasm. D. They control gene expression. E. They regulate the synthesis of DNA in response to a signal. D One of the major categories of receptors in the plasma membrane reacts by forming dimers, adding phosphate groups,
and then activating relay proteins. Which type does this? A. ligand-gated ion channels B. receptor tyrosine kinases C. G protein-coupled receptors D. steroid receptors B Use this description to answer the following question.A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others. Where would you expect to find the carboxyl end? A. between the membrane layers B. at the exterior surface C. at the cytosol surface D. connected with the loop at H5 and H6 C Use this description to answer the following question. A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others. The coupled G protein most likely interacts with this receptor A. along the exterior margin. B. along the interior margin. C. at the loop between H5 and H6. D. at the NH3 end. E. at the COO- end. C Testosterone functions inside a cell by A. acting as a signal receptor that activates tyrosine kinases. B. coordinating a phosphorylation cascade that increases spermatogenesis. C. acting as a steroid signal receptor that activates ion channel proteins. D. binding with a receptor protein that enters the nucleus and activates specific genes. E. becoming a second messenger that inhibits nitric oxide. D
If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system? A. It could activate only the epinephrine system. B. It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane. C. It would be able to carry out reception and transduction but would not be able to respond to a signal. D. It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane. E. It would employ a transduction pathway directly from an external messenger. B When protein membrane receptors are activated, what usually happens? A. The receptors open and close in response to protein signals. B. A change occurs on only one membrane surface: exterior or interior. C. The receptor preferentially binds with lipid or glycolipid signal molecules. D. A change occurs in intracellular ion concentration. E. The receptor changes conformation after binding with signal polypeptides. E Particular receptor tyrosine kinases (RTKs) that promote excessive cell division are found at high levels on various cancer cells. A protein, Herceptin, has been found to bind to an RTK known as HER2. HER2 is sometimes excessive in cancer cells. This information can now be utilized in breast cancer treatment if which of the following is true? A. If the patient's cancer cells have excessive levels of HER2. B. If HER2, administered by injection, causes cell division. C. If the patient has RTKs only in cancer cells. D. If Herceptin is found in the breast lymph nodes of the patient. E. If the patient's genome codes for the HER2 receptor. A Which of the following is true of steroid receptors? A. The receptor may be inside the nuclear membrane. B. The receptor molecules are free to move in and out of most organelles. C. The receptor molecules are themselves lipids or glycolipids. D. The unbound steroid receptors are quickly recycled by lysosomes. E. The concentration of steroid receptors must be relatively high in most cells.
A Which of the following are among the most common second messengers? A. kinase and phosphate groups B. G proteins and GTP C. kinase and phosphatase D. GTP and GDP E. calcium ion and cAMP E Which of the following sequences is correct? A. binding of a signaling molecule to its receptor G protein activation adenylyl cyclase activation cAMP production protein phosphorylation B. diffusion of a signaling molecule across the plasma membrane binding of the signaling molecule to its receptor movement of the signaling molecule-receptor complex into the nucleus transcription C. binding of a growth factor to its receptor phosphorylation cascade activation of transcription factor transcription D. binding of a signaling molecule to its receptor G protein activation phospholipase C activation IP3 production increase in cytoplasmic calcium concentration E. All of the choices are correct. E →
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Which of the following is the best explanation for the inability of a specific animal cell to reduce the Ca2+ concentration in its cytosol compared with the extracellular fluid? A. loss of transcription factors B. blockage of the synaptic signal C. low oxygen concentration around the cell D. insufficient ATP levels in the cytoplasm E. low levels of protein kinase in the cell D An inhibitor of phosphodiesterase activity would have which of the following effects? A. prolong the effect of epinephrine by maintaining elevated cAMP levels in the cytoplasm B. decrease the amount of cAMP in the cytoplasm C. block the response of epinephrine D. block the activation of G proteins in response to epinephrine binding to its receptor E. block the activation of protein kinase A A
Adenylyl cyclase has the opposite effect of which of the following? A. GTPase B. phosphodiesterase C. protein phosphatase D. protein kinase E. phosphorylase B Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of A. GTP. B. phosphorylated proteins. C. cAMP. D. adenylyl cyclase. E. activated G proteins. C If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound A. that increases phosphorylase activity. B. to block G protein activity in liver cells. C. that activates epinephrine receptors. D.that increases cAMP production in liver cells. E. that keeps sugar molecules from crossing the plasma membrane of liver cells. B If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound A. that increases phosphodiesterase activity. B. to stimulate G protein activity in liver cells. C. that mimics epinephrine and can bind to the epinephrine receptor. D. that stimulates cAMP production in liver cells. E. that does any of the above. A An inhibitor of which of the following could be used to block the release of calcium from the endoplasmic reticulum? A. adenylyl cyclase B. tyrosine kinases C. phospholipase C
D. serine/threonine kinases E. phosphodiesterase C Which of the following statements is true of signal molecules? A. When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules. B. In most cases, signal molecules interact with the cell at the plasma membrane and then enter the cell and eventually the nucleus. C. In response to some G protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium. D. Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in phosphodiesterase activity in the absence of an appropriate signal molecule. E. Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors. E Which of the following is a correct association? A. phosphorylase activity and the catabolism of glucose B. kinase activity and the addition of a tyrosine C. adenylyl cyclase activity and the conversion of cAMP to AMP D. phosphodiesterase activity and the removal of phosphate groups E. GTPase activity and hydrolysis of GTP to GDP E Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction? A. glycine and histidine B. tyrosines C. serine and threonine D. glycine and glutamic acid E. Any of the 20 amino acids are equally phosphorylated. c The function of phosphatases in signal transduction is best described as to A. inactivate protein kinases and turn off the signal transduction. B. amplify the second messengers such as cAMP. C. prevent a protein kinase from being reused when there is
another extracellular signal. D. move the phosphate group of the transduction pathway to the next molecule of a series. E. amplify the transduction signal so it affects multiple transducers. A What explains the increased concentration of in the ER? A. Calcium levels in the blood or other body fluids are extremely low. B. Calcium concentration is kept low in the cytoplasm because of its high usage level. C. Calcium cannot enter the plasma membrane through ion channels. D. Calcium ions are actively imported from the cytoplasm into the ER. E. The CA+ ions are recycled from other molecules in the ER. D The toxin of Vibrio cholerae causes profuse diarrhea because it A. modifies a G protein involved in regulating salt and water secretion. B. modifies calmodulin and activates a cascade of protein kinases. C. signals IP3 to act as a second messenger for the release of calcium. D. binds with adenylyl cyclase and triggers the formation of cAMP. E. decreases the cytosolic concentration of calcium ions, making the cells hypotonic. A Which of the following would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins? A. G protein-coupled receptor binding B. ligand-gated ion channel signaling C. receptor tyrosine kinase activity D. adenylyl cyclase activity E phosphatase activity C Viagra causes dilation of blood vessels and increased blood flow to the penis, facilitating erection. Viagra acts by inhibiting A. the hydrolysis of cGMP to GMP. B. the removal of GMP from the cell. C. the phosphorylation of GDP.
D. the dephosphorylation of cGMP. E. the hydrolysis of GTP to GDP. A In general, a signal transmitted via phosphorylation of a series of proteins A. allows target cells to change their shape and therefore their activity. B. requires binding of a hormone to a cytosol receptor. C. requires phosphorylase activity. D. brings a conformational change to each protein. E. cannot occur in yeasts because they lack protein phosphatases. D Which of the following most likely would be an immediate result of growth factor binding to its receptor? A. phosphorylase activity B. protein kinase activity C. protein phosphatase activity D. adenylyl cyclase activity E. GTPase activity B In which of the following ways could signal transduction most probably be explored in research to treat cancer? A. increase in the concentration of phosphodiesterases in order to produce more AMP B. alteration of protein kinases in cell cycle regulation in order to slow cancer growth C. removal of serine/threonine phosphate acceptors from transduction pathways in colon pre-cancerous growths D. expansion of the role of transduction inhibitors in the cells before they give rise to cancer E. increase in calcium ion uptake into the cytoplasm in order to modulate the effects of environmental carcinogens B Sutherland discovered that the signaling molecule epinephrine: A. elevates cytosolic concentrations of cyclic AMP. B. interacts directly with glycogen phosphorylase. C. causes lower blood glucose by binding to liver cells. D. brings about a decrease in levels of cAMP as a result of bypassing the plasma membrane. E. interacts with insulin inside muscle cells. A
For the greatest advantage of multiple steps in a transduction pathway is: A. Each individual step can remove excess phosphate groups from the cytoplasm. B. Having multiple steps provides for greater possible amplification of a signal. C. Each step can be activated by several G proteins simultaneously. D. Many of the steps can be used in multiple pathways. E. Having multiple steps in a pathway requires the least amount of ATP. B Why are there often so many steps between the original signal event and the cell's response? A. Long, highly specific pathways minimize the possibility that a relay molecule accidentally could activate a pathway leading to a secondary response. B. The accumulation of genetic mutations over time has added redundant steps to the pathway. C. Each transduction is a checkpoint. D. Lengthy pathways provide the opportunity for the initial pathway molecules to recycle back to inactive forms should additional signaling molecules be present. E. Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses. E Why can a signaling molecule cause different responses in different cells? A. Different cells possess different enzymes, which modify the signaling molecule into different molecules after it has arrived. B. Different cells have membrane receptors that bind to different sides of the signaling molecule. C. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor. D. The transduction pathway in cells has a variable length. E. All of the above are correct. C A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following? A. a decrease in G protein activity B. an increase in receptor tyrosine kinase activity C. an increase in cytosolic calcium concentration
D. a decrease in transcriptional activity of certain genes E. lower cytoplasmic levels of cAMP D At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects? A. Estrogen is produced in very large concentration and therefore diffuses widely. B. Estrogen is kept away from the surface of any cells not able to bind it at the surface. C. Estrogen has specific receptors inside several cell types, but each cell responds in the same way to its binding. D. Estrogen binds to specific receptors inside many kinds of cells, each of which have different responses to its binding. E. The subcomponents of estrogen, when metabolized, can influence cell response. D What are scaffolding proteins? A. microtubular protein arrays that allow lipid-soluble hormones to get from the cell membrane to the nuclear pores B. ladderlike proteins that allow receptor-ligand complexes to climb through cells from one position to another C. large molecules to which several relay proteins attach to facilitate cascade effects D. relay proteins that orient receptors and their ligands in appropriate directions to facilitate their complexing E. proteins that can reach into the nucleus of a cell to affect transcription C GTPase activity is important in the regulation of signal transduction because it A. phosphorylates protein kinases. B. converts cGMP to GTP. C. hydrolyzes GTP to GDP thus shutting down the pathway. D. decreases the amount of G protein in the membrane. E. increases the available concentration of phosphate. C What is apoptosis? A. a way to stimulate transcription B. a type of second messenger C. a type of membrane receptor
D. controlled cell suicide E. a metabolic step in blood clotting D Why has C. elegans proven to be a useful model for understanding apoptosis? A. The animal has as many genes as complex organisms, but finding those responsible is easier than in a more complex organism. B. While the organism ages, its cells die progressively until t he whole organism is dead. C. All of its genes are constantly being expressed so all of its proteins are available from each cell. D. The nematode undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development. E. This plant has a long-studied aging mechanism that has made understanding its death just a last stage. D Why is apoptosis potentially threatening to the healthy "neighbors" of a dying cell? A. Released cellular energy would interfere with the neighbors' energy budget. B. Neighboring cells would activate immunological responses. C. Cell death would usually spread from one cell to the next via paracrine signals. D. Lysosomal enzymes exiting the dying cell would damage surrounding cells. E. Bits of membrane from the dying cell could merge with neighbors and bring in foreign receptors. D In C. elegans, ced-9 prevents apoptosis in a normal cell in which of the following ways? A. Ced-9 remains inactive until it is signaled by ced-3 and other caspases. B. Ced-9 cleaves to produce ced-3 and ced-4. C. It prevents the caspase activity of ced-3 and ced-4. D. Ced-9 prevents blebbing by its action on the cell membrane. E. Ced-9 enters the nucleus and activates apoptotic genes. C Which of the following describes the events of apoptosis? A. The cell's DNA and organelles become fragmented, the cell dies, and it is phagocytized. B. The cell dies, and the presence of its fragmented content s stimulates nearby cells to divide.
