Cell Biology Chapter 15

Match the cell adhesion or junction on the left with the appropriate choice on the right. A) junction connecting tonofilaments to collagen filaments B) anchors cytoskeleton of one cell with that of a neighboring cell C) type of adherens junction connecting actin filaments to the extracellular matrix D) dense cluster of intracellular linker proteins connected to cytoskeletal filaments E) protein subunit of gap junctions F) continuous attachment zones connecting actin microfilament structures near the apical end of epithelial cells G) button-like point of strong adhesion between two cells H) intermediate filaments associated with plaques I) create a permeability barrier between epithelial cells J) an adhesive junction that connects an epithelial cell to the basal lamina K) hollow cylinders associated with gap junctions L) connects cytoplasms of two cells M) specialized modifications of the cell membrane in which two cells come together in multicellular organisms 1) adherens junctions 2) desmosome 3) cell junctions 4) connexons 5) plaque 6) tonofilaments 7) hemidesmosome 8) adhesive junction 9) tight junctions 10) connexin 11) gap junction 12) focal adhesion

1) adherens junctions - F) continuous attachment zones connecting actin microfilament structures near the apical end of epithelial cells 2) desmosome - G) button-like point of strong adhesion between two cells 3) cell junctions - M) specialized modifications of the cell membrane in which two cells come together in multicellular organisms 4) connexons - K) hollow cylinders associated with gap junctions 5) plaque - D) dense cluster of intracellular linker proteins connected to cytoskeletal filaments 6) tonofilaments - H) intermediate filaments associated with plaques 7) hemidesmosome - J) an adhesive junction that connects an epithelial cell to the basal lamina 8) adhesive junction - B) anchors cytoskeleton of one cell with that of a neighboring cell 9) tight junctions - I) create a permeability barrier between epithelial cells 10) connexin - E) protein subunit of gap junctions 11) gap junction - L) connects cytoplasms of two cells 12) focal adhesion - C) type of adherens junction connecting actin filaments to the extracellular matrix 1) F 2) G 3) M 4) K 5) D 6) H 7) J 8) B 9) I 10) E 11) L 12) C

7) Animal cells attach to adhesive glycoproteins such as ________ and ________ in the extracellular matrix.

Answer: fibronectin; laminin

15) A major component of collagen is the amino acid ________, which is the only one small enough to fit in the interior of the collagen triple helix structure.

Answer: glycine

6) A cadherin forms a ________ extracellular interaction with a ________ on another cell.

Answer: homophilic; cadherin

11) Free ________ molecules provide lubrication to joints between movable bones.

Answer: hyaluronate

1) The ________ is the layer of cell wall material shared between adjacent plant cells.

Answer: middle lamella

10) One of the most important roles of proteoglycans is to trap ________ to form a ________ matrix.

Answer: water; gelatinous

45) Expansins are proteins that loosen up cell walls so cells can elongate. Auxin is thought to activate expansins by A) aligning cellulose microfibrils. B) activating protons pumps to decrease pH in a section of the cell wall. C) depositing lignin molecules between cellulose fibrils. D) increasing turgor pressure. E) increasing pectin hydration.

B) activating protons pumps to decrease pH in a section of the cell wall.

25) Elastin molecules are crosslinked to each other by A) hydrogen bonds between hydroxylysines and hydroxyprolines. B) covalent bonds between lysines. C) covalent bonds between prolines. D) hydrophobic interactions between hydroxyprolines and glycines. E) peptide bonds between glycines.

B) covalent bonds between lysines

6) Which of the following junctions is most abundant in tissues such as skin that are required to resist significant mechanical stress? A) gap junctions B) desmosomes C) focal adhesions D) tight junctions E) All are abundant in tissues resisting stress.

B) desmosomes desmosomes are especially abundant in the skin muscle, and the neck of the uterus

18) Which of the following pairs shares a similar function? A) adhesive junction-tight junction B) desmotubule-gap junction C) tight junction-gap junction D) plaque-plasmodesma E) connexon-desmosome

B) desmotubule-gap junction desmotubule is a tubular structure that permits direct cell-cell communication through the cell wall

13) You discover a dog suffering from an autoimmune response. On further investigation, you find that the cells of various tissues are loosely arranged and do not have characteristic shapes, and the animal is prone to hemorrhaging because of poor blood clotting. Based on these results, the target of the autoimmune response is most likely to be A) fibronectins. B) laminins. C) extensins. D) pectins. E) elastins.

A) fibronectins Fibronectinacts as a bridging molecule between cells and the ECM. Once attached, cells flatten and their actin cytoskeletons align with the fibronectinoutside the cell.

32) The type of adhesive junction that connects epithelial cells to the basal lamina is a A) hemidesmosome. B) desmosome. C) gap junction. D) tight junction. E) focal contact.

A) hemidesmosome

37) Each of the following is a component of the plant cell wall network except A) hyaluronate. B) cellulose. C) extensin. D) hemicellulose. E) pectin.

A) hyaluronate.

14) The finding that integrin-linked kinase (ILK) is required for focal adhesion function but its kinase activity is not, suggests the protein acts as a A) direct connection to the ECM. B) linker protein. C) scaffolding protein. D) cytoskeletal filament. E) signaling protein.

C) scaffolding protein. ILK probably functions as a scaffolding protein during integrin-based signaling, because "kinase dead" versions of the protein still function.

7) The primary function of each of the following is for adhesion of a cell to another cell or the extracellular matrix except A) desmosomes. B) hemidesmosomes. C) plaques. D) connexins. E) cadherins.

D) connexins. connexin is part of the gap junction which does cell-cell communication plaque is part of the desmosome structure

2) Polarized cells are characterized by A) random orientation within a tissue. B) being surrounded on all sides by a basement membrane. C) junctions only to ECM and not to other cells. D) distinct apical and basolateral ends of the cell. E) formation of several connected layers of cells.

D) distinct apical and basolateral ends of the cell.

29) Collagens interact directly with which of the following types of junctions? A) gap junctions B) tight junctions C) hemidesmosomes D) desmosomes E) None of the above are correct.

E) None of the above are correct.

8) Numerous collagen fibrils associate to form a collagen ________.

Answer: fiber

30) The primary function of focal contacts is A) cell-ECM adhesion. B) cell-cell adhesion. C) cell-cell communication. D) paracellular pathway regulation. E) establishing cell polarity.

A) cell-ECM adhesion.

24) Each of the following is a good functional match between animal and plant extracellular structures or fibers except A) elastins-extensins. B) extracellular matrix-cell wall. C) collagens-cellulose. D) proteoglycans-hemicelluloses. E) fibronectins-pectins.

A) elastins-extensins Plant cell walls consist of mainly long cellulose microfibrilsenmeshed in a network of - Branched glycoproteins called extensins

10) Selectins mediate interactions between which of the following? A) leukocytes and blood vessel endothelial cells B) muscle cells and ECM C) nerve cells and other nerve cells D) intestinal epithelial cells with neighboring cells E) skin cells in different skin layers

A) leukocytes and blood vessel endothelial cells Different selectins on different cell types E-selectin-endothelial, L-selectin on leukocytes. During inflammation leukocytes attached to endothelial cells and migrate through blood vessel to damage site.

12) Which of the following is the correct order for the synthesis of the plant cell wall? A) middle lamella; primary cell wall; secondary cell wall B) primary cell wall; middle lamella; secondary cell wall C) secondary cell wall; primary cell wall; middle lamella D) middle lamella; secondary cell wall; primary cell wall E) primary cell wall; secondary cell wall; middle lamella

A) middle lamella; primary cell wall; secondary cell wall

43) Each of the following is true about plant pectins except A) pectins are long unbranched polymers. B) pectins form the matrix in which cellulose microfibrils are embedded. C) pectins bind adjacent cell walls together. D) pectins trap and bind water molecules. E) pectins have a gel-like consistency.

A) pectins are long unbranched polymers.

5) An autoimmune disorder in which an immune response targets Type V collagen fibers is most likely to affect the A) skin. B) heart. C) lungs. D) stomach. E) tongue.

A) skin. collegen is located at the basal lamina right under the epithelial cell layer

1) You are investigating the activity of different cadherins in cells. You use recombinant DNA technology to express GFP-E-cadherin (green) in some L-cells (which do not normally contain cadherin) and YFP-P-cadherin (yellow) in other L-cells. Explain results you expect in three cultures containing: (1) only cells expressing GFP-E-cadherin, (2) only cells expressing YFP-P-cadherin, and (3) a mixture of GFP-E-cadherin-expressing and YFP-P-cadherin-expressing cells. Also predict how (a) knocking down the ability of the cells to synthesize fibronectin (FN) or (b) adding EGTA, which depletes free Ca2+ concentration in the culture medium, might affect the results.

Answer: 1) The GFP-E-cadherin-expressing cells would form adherens junctions (labeled green) with one or more cells, possibly forming a sheet of cells. 2) The YFP-E-cadherin-expressing cells would form adherens junctions (labeled yellow) with one or more cells, possibly forming a sheet of cells. 3) Both cell types would form adherens junctions but only with cells expressing the same type of cadherin, because cadherin extracellular interactions are cadherin-type specific. a) Cells expressing either labeled cadherin would be expected to form adherens junctions regardless of whether they can synthesize FN or not, but they may not adhere and spread on the substrate as well without FN. b) Medium lacking Ca2+ will not support the formation of cadherin-dependent adherens junctions, because cadherin-cadherin interaction depends on the presence of extracellular Ca2+.

2) Describe experiments using marker molecules that have been done to elucidate important properties of (1) tight junctions and (2) gap junctions, and propose one additional experiment you could do with each junction to gain a greater understanding of that junction's properties.

Answer: 1) When an electron-opaque tracer was added to the basolateral side of an epithelial layer, the tracer penetrated in the intracellular space between the cells, past desmosomes and the adherens junction, up to the position of the tight junction. The tracer did not pass through the tight junction. This demonstrated the barrier property of the tight junction in regulating paracellular transport, at least from the basolateral side to the apical side. A possible additional experiment would be to add the tracer to the apical side of the epithelium to assess whether the tight junction also blocks paracellular transport from that direction. 2) Microinjection of various sizes of fluorescent molecules into one cell connected to another by gap junctions revealed that gap junctions pass molecules between the cytoplasms of cells that are up to a size limitation of ~1200 Daltons MW. A possible additional experiment would be to test molecules of different shapes, say long linear molecules that are >1200 D, or molecules with different chemical characteristics to determine whether size is the only limitation. Another possible experiment would be to determine what happens to gap junctions when one of the cells dies, perhaps by loading one cell with a small fluorescent probe and then puncturing the other cell to determine whether the dye leaks from the living cell gap junctions or whether the gap junctions can close.

5) Cancer cells exhibit a variety of differences from normal cells in cell adhesion, cell junctions, and cell effects on the extracellular matrix, some of which facilitate metastasis. Explain three changes found in some cancer cells related to these aspects of cell structure and function.

Answer: Answers may include the following: 1) Cells may stop producing E-cadherin or other cadherins, which may be associated with an epithelial-mesenchymal transition and subsequent metastasis. 2) Cells may increase MMP secretion, which can cause localized ECM breakdown and facilitate metastasis through the ECM. 3) Cells may increase binding to the basal lamina, which can facilitate metastasis cell motility. 4) Cells may decrease synthesis and secretion of fibronectins, resulting in loss of cell shape and detachment from the ECM. 5) Cells may develop focal adhesion unresponsiveness to the Wnt signaling pathway, which normally would repress cell division and motility. 6) Cells may lose anchorage-dependence for growth, possibly through permanent FAK activation.

5) ________ are Ca2+-dependent adhesive glycoproteins that function in animal cell-cell recognition and adhesion.

Answer: Cadherins

3) Discuss the role of claudins in the structure and functions of tight junctions. Propose what might change for a tight junction in which charged amino acids in the claudin large extracellular loop are mutated to nonpolar amino acids.

Answer: Claudin extracellular loop domains form homophilic interactions that are a barrier to paracellular transport through intercellular spaces between epithelial cells. Charged amino acids in the claudin large extracellular loop form ion-selective pores that allow the passage of specific ions through the barrier. Mutation of the charged amino acids to nonpolar ones would create a more hydrophobic region that could block ion transport but allow passage of nonpolar substances that fail to pass through wild-type claudins. This would change the barrier function of the tissue and could affect the health of the organism. Recessive mutations in one type of claudin result in an inherited disorder characterized by severe Mg2+ and Ca2+ imbalance.

4) Amniocentesis and genetic screening reveal that a fetus carries a defective L1-CAM gene. What defects do you expect, and why?

Answer: During embryogenesis N-CAM and L1-CAM function in the outgrowth and the bundling of neurons. Individuals expressing a defective L1-CAM will have defects in the brain corpus callosum, causing mental retardation and other neural defects.

9) ________ are polysaccharides composed of repeating disaccharide units that are the carbohydrate part of some proteoglycans.

Answer: Glycosaminoglycans (GAGs)

13) ________ are the animal cell surface proteins that link the cytoskeleton to the extracellular matrix.

Answer: Integrins

3) ________ are insoluble polymers of aromatic alcohols that primarily are found in woody tissues.

Answer: Lignins

2) ________ are cytosolic channels through openings in plant cell walls.

Answer: Plasmodesmata

4) A(n) ________ is the ring of cytoplasm through a plasmodesmata.

Answer: annulus

12) The ________ serves as structural support in tissue organization and as a permeability barrier.

Answer: basal lamina

14) The three most common glycosaminoglycans (GAGs) are ________, ________, and ________.

Answer: chondroitin sulfate; keratan sulfate; hyaluronate

28) To investigate the role of cadherin in early development, you continuously treat frog zygotes with antibodies that bind EP-cadherin. You most likely would find that A) cell division stops but the existing cells organize to form a small, properly organized blastula. B) the cells associate only loosely and fail to form a properly organized blastula. C) the cells associate only loosely but skip the blastula stage to develop into a normal frog. D) the cells divide uncontrollably and form a large tumor-like mass. E) blastula formation and subsequent development proceed normally

B) the cells associate only loosely and fail to form a properly organized blastula.

1) Which of the following stabilizes homophilic interactions between the extracellular domains of cadherins on neighboring cells? A) hyaluronate B) proteoglycans C) Ca2+ D) integrins E) talin

C) Ca2+

4) In animals, the extracellular matrix plays important roles in each of the following processes except A) cell division. B) cell motility. C) DNA replication. D) cell differentiation. E) cell adhesion.

C) DNA replication

17) Ehlers-Danlos syndrome and scurvy both are characterized by defects in A) fibronectin. B) desmosomes. C) collagen. D) dystrophin. E) elastin.

C) collagen. Collagens Are Responsible for the Strength of the Extracellular Matrix The collagen and elastin fibers are enmeshed in a gel-like network of proteoglycans Ehlers-Danlos syndrome causes elastic skin to bruise easily and overly flexible joints

22) Which of the following aspects of collagen would be directly affected by a defect in procollagen peptidase? A) synthesis B) secretion C) extracellular assembly D) binding to fibronectin E) all of the above

C) extracellular assembly

8) Mice lacking plakoglobin have skin defects but usually die from A) cancer. B) muscular dystrophy. C) heart failure. D) Ehlers-Danlos syndrome. E) scurvy.

C) heart failure. planktoglobin is a catenin that is part of a desmosome

21) Which of the following is associated with the lubrication of joints? A) chondroitin sulfate B) lignins C) hyaluronate D) keratan sulfate E) pectins

C) hyaluronate a glycosaminoglycan found in high concentration in the extracellular matrix where cells are actively proliferating or migrating, and in the joints between movable bones.

35) In cartilage, proteoglycans form large complexes by attaching to A) glycosaminoglycans. B) collagen. C) hyaluronate. D) laminin. E) elastin

C) hyaluronate.

34) Animal extracellular matrices contain each of the following except A) collagens. B) proteoglycans. C) pectins. D) fibronectins. E) elastins.

C) pectins. pectins are found in the primary cell wall

39) A cluster of intracellular linker proteins associated with a junction is called a(n) A) annulus. B) connexon. C) plaque. D) tonofilament. E) accessory protein complex.

C) plaque. Many adhesion receptors also interact with the cytoskeleton via linker proteins

36) Costameres, in which cytosolic actin filaments are linked to extracellular laminins through dystrophin-dystrogylcan complexes, are found in A) skin cells. B) intestinal epithelial cells. C) striated muscle cells. D) nerve cells. E) pancreatic cells.

C) striated muscle cells. Adhesive glycoproteins, fibronectins and lamins,that allow cells to attach to the matrix

27) You suspect that an elderly patient's skin blistering is caused by an autoimmune disorder. If you are correct, the patient's serum likely contains antibodies directed against A) talin. B) vinculin. C) α-actinin. D) BPAG2. E) actin.

D) BPAG2. serve as a bridge between keratin and laminin Like desmosomes, hemidesmosomes are crucial for the mechanical strength of skin; devastating effects on human health can result when desmosome or hemidesmosome components are defective or missing

20) While investigating a medical condition, you discover that the patient has an autoimmune disease that targets and destroys fibroblasts. This disorder would most likely affect A) fibrin activity in blood clotting. B) annulus formation. C) hyaluronate lubrication of joints. D) collagen production. E) primary cell wall deposition.

D) collagen production.

9) N-CAM mediates interactions between neural cells and is a member of which of the following protein families? A) catenins B) cadherins C) selectins D) immunoglobulin superfamily (IgSF) proteins E) lectins

D) immunoglobulin superfamily (IgSF) proteins

33) Which of the following forms the insoluble layer of aromatic alcohols found primarily in woody tissues? A) hyaluronates B) cadherins C) proteoglycans D) lignins E) pectins

D) lignins very insoluble complex polymers of aromatic alcohols found mainly in woody tissues They are localized between cellulose fibrils

41) Although MCF-10A breast cancer cells grow well on Matrigel-coated culture dishes, the cells will form cysts of polarized cells that produce milk only when A) extra collagen is added to the Matrigel. B) extra fibronectin is added to the Matrgel. C) extra elastin is added to the Matrigel. D) the Matrigel layer is thick enough to form a 3D environment. E) the Matrigel layer is present as a very thin layer on the culture dishes.

D) the Matrigel layer is thick enough to form a 3D environment.

31) Which of the following is responsible for the impermeability of the epithelium lining the bladder and ducts connecting the pancreas to the digestive tract? A) adherens junctions B) gap junctions C) desmosomes D) tight junctions E) hemidesmosomes

D) tight junctions

19) Which of the following regulates paracellular transport? A) adherens junctions B) gap junctions C) desmosomes D) tight junctions E) hemidesmosomes

D) tight junctions Tight junctions form a permeability barrier between epithelial cells, and they prevent the lateral movement of membrane proteins, thereby partitioning the membrane into discrete functional domains. They also mediate paracellular transport across epithelia.

3) Each of the following cell junctions is found in intestinal epithelial cells except A) gap junctions. B) hemidesmosomes. C) tight junctions. D) desmosomes. E) All are found in intestinal epithelial cells.

E) All are found in intestinal epithelial cells. hemidesmosomes are found in epithelial cells; they contain specific integrin the integrins are attached to IF keratin

38) Which of the following is a primary structural constituent of the plant cell secondary wall? A) hemicellulose B) extensin C) collagen D) pectin E) cellulose

E) cellulose Cellulose and lignins are the primary constituents of the secondary cell wall

42) Each of the following proteins is a component of both costameres and focal adhesions except A) β1-integrin. B) vinculin. C) talin. D) α-actinin. E) dystrophin.

E) dystrophin. The costamere is an attachment structure at the surface of striated muscle. Costameres contain many of the same proteins found at focal contacts in addition to the protein dystrophin. Migratory and non-epithelial cells such as fibroblasts attach to ECM molecules via focal adhesions

26) Each of the following is true about basal lamina except A) it serves as a structural support. B) it allows for movement of some small molecules but blocks movement of large molecules. C) it can influence cell migrations in certain areas of the body. D) it contains collagen type IV, proteoglycans, laminins, and entactin. E) it is composed primarily of fibronectin.

E) it is composed primarily of fibronectin.

23) Which of the following could you use experimentally to help you determine which carbohydrates are present on a cell's surface? A) cadherins B) proteoglycans C) pectins D) connexins E) lectins

E) lectins Carbohydrate-binding proteins secreted by plants and animals

11) Each of the following components is associated with the primary cell wall except A) cellulose microfibrils. B) hemicelluloses. C) pectins. D) glycoproteins. E) lignins.

E) lignins. The primary cell wall, formed while cells are still growing, a loosely organized network of cellulose, hemicellulose, pectins, and glycoproteins lignins are in woody tissues very insoluble complex polymers of aromatic alcohols found mainly in woody tissues

40) Fibronectin interacts with each of the following except A) fibrin. B) collagen. C) heparin. D) integrin. E) pectin.

E) pectin.

15) Each of the following is a component of focal adhesions except A) integrin. B) talin. C) α-actinin. D) vinculin. E) plakoglobin.

E) plakoglobin. integrins and the cytoskeleton - focal adhesion Migratory and non-epithelial cells such as fibroblasts attach to ECM molecules via focal adhesions These contain clustered integrinsthat interact with bundles of actin filaments via talin, and other MF associated proteins planktoglobin is a catenin that is part of a desmosome

44) Each of the following is true about plant rosettes except A) rosettes are localized in the plasma membrane. B) rosettes are cellulose-synthesizing enzyme complexes. C) rosette deposition of cellulose microfibrils is directed by microtubules. D) rosettes move in the plasma membrane to deposit growing cellulose microfibrils. E) rosettes deposit cellulose microfibrils only in the middle lamella.

E) rosettes deposit cellulose microfibrils only in the middle lamella.

16) Which of the following functions like a fence to block membrane protein movement between the apical and basolateral regions of an intestinal epithelial cell plasma membrane? A) gap junctions B) desmosomes C) adherens junction D) hemidesmosomes E) tight junction

E) tight junction