BIO-333 Chapter 19 Guide 7e PDF

Name\_Isabel Hernandez Carrillo\_ BIO-333 Chapter 19 Guide 7e 1\. (pgs. 1105-118, figs. 19-1, 19-2, and 19-3, Table 19-1) What are the two broad types of cell linkages? What bears most of the mechanical stress in tissues? Briefly list and describe the types of cell junctions in figure 19-2. Be fami...

Name\_Isabel Hernandez Carrillo\_ BIO-333 Chapter 19 Guide 7e 1\. (pgs. 1105-118, figs. 19-1, 19-2, and 19-3, Table 19-1) What are the two broad types of cell linkages? What bears most of the mechanical stress in tissues? Briefly list and describe the types of cell junctions in figure 19-2. Be familiar with the types of junctions listed in table 19-1. - Cell linkage: Direct interactions or held together w/in extracellular matrix (network of proteins and polysaccharide chains) - Junction anchors withstand mechanical stress in tissues. - They attach cells to neighboring cells/extracellular matrix. - Type of junctions: - Tight- Seals gap between epithelial cells - Cell to cell anchoring: - Adherens junction- Connects actin filament bundle in one cell w/that in the next cell - Desmosome- Connects intermediate filaments in one cell to those in the next cell. - Channel-forming: - Gap junction- Allows passage of small water-soluble molecules from cell to cell. - Cell-matrix anchoring: - Actin-linked cell-matrix- Anchors actin filaments in cell to extracellular matrix. - Hemidesmosome- Anchors intermediate filaments in cell to extracellular matrix. - Transmembrane adhesion proteins- One end linking to cytoskeleton inside the cell and the other end linking to other structures outside the cell. - Integrin- Involved attachment of cells to the extracellular matrix and to each other.   **Figure** **19-1: Two major tissue types.** 2\. (pgs. 118-1010, figs. 19-4, 19-5, and 19-6) Describe cadherins, what groups make up the cadherin superfamily? What is meant by homophilic binding? Describe how cadherins bind to each other (what ion is necessary) and how these attachments break. Are the attachment sites between cadherins strong? - Cadherin- Mediates homophilic Ca2+ dependent cell-cell adhesion in animal tissues. - Types: - Classical: Includes E (epithelial cells), N (nerve, muscle, and lens cells), P (placenta and epidermis), that are closely related in sequence throughout their extracellular and intracellular domains. - Nonclassical: More distantly related in sequence than classical cadherins and include proteins involved in adhesion (includes protocadherins, desmocollins, and desmogleins= desmosomes) and signaling. - Homophilic binding- Binding between molecules of the same kind (cell-cell adhesion). - These bindings occurs at the N-terminal tops creating a knob and nearby pocket. Ca2+ ions bind to sites near each hinge (pocket) and prevents it from flexing allowing for a rigid and slightly curved rod. When Ca2+ is removed that hinge can flex and becomes floppy. Therefore, weaking the conformation of the N-terminus and affecting its binding affinity for matching cadherin molecule on the opposite cell. - Strength: Individual attachment is weak but clustering of cadherins on cell membranes coupled with cytoskeleton connection= strong.  **Figure 19-5: Bindings** 3\. (pgs. 1110-1111, figs. 19-8 and 19-9) Discuss the specificity of cadherins. Describe the changing patterns of cadherin expression during nervous system development in vertebrates. Describe the sorting out process in figure 19-9. - Caherins mediate highly selective recognition enabling cells of similar types to stick together and to stay segregated from other types of cells. - Level of cadherins expressed - Nervous system development: - Neural tube cells lose E-cadherin and acquire other cadherins including N-cadherins. Cells in overlying ectoderm continue to express E-cadherin. When the neural crest cells migrate away from the neural tube, cadherins become scarcely detectable and cadherin 7 appears to help hold the migrating cells together as loosely associated cell groups. When neural crest cells aggregate to form a ganglion they switch on expression of N-cadherin again. If overexpression occurs the cells fail to escape from the neural tube. - Figure 19-9: B) Cells expressing high levels of cadherin adhere more strongly and congregate internally. A diagram of a number Description automatically generated **Figure 19-8: Changing pattern of cadherins expression during construction of vertebrates nervous system.** 4\. (pgs. 1112-1114, figs. 19-10, 19-11, and 19-12) Describe the location and function of the catenins. Describe the assembly of an adherens junction. Describe why these sites are examples of mechanotransduction? What is role of vinculin in this process? - Catenins- Located at cell-cell junctions (w/in adherens junctions) acting as crucial linkers between cadherin adhesion molecules and actin cytoskeleton effectively holding cells together and maintaining tissue integrity. - β-catenin, p120-catenin, and α-catenin - Adherens junctions (AJ)- Linked through catenins to contractile bundles of actin and myosin II. They are subjected to pulling forces generated by attached actin - Mechanotransduction- Junctions that are able to sense mechanical stresses and generate biochemical signals that lead to an appropriate response. - AJ senses the forces acting on them and modify local actin and myosin behavior to balance forces on both sides of junction. - Vinculin- Promotes recruitment of more actin to junction when protein α-catenin is stretched from a folded to an extended conformation when contractile activity increases at junction. Diagram of a diagram showing how the surface is exposed Description automatically generated with medium confidence **Figure 19-10: Local changes in cortical tension promote initial** **formation of adherens junction.**  5\. (pgs. 1114-1116, figs. 19-13 and 19-14) Describe the function and components of an adhesion belt. Describe the process of folding an epithelial sheet into an epithelial tube. - Adhesion belt- AJ in epithelia that form a continuous belt (zonula adherens) just beneath the apical face of the epithelium, encircling each of the interacting cells in the sheet. - Components: Cadherin, catenin, and actin cytoskeleton. - Epithelia sheet to tube folding: - Oriented contraction of bundles of actin and myosin filaments running along adhesion belts causes epithelial cells to narrow at their apical surface, thereby helping epithelial sheet to roll up into a tube.  6\. (pgs. 1116-1117, figs. 19-16 and 19-17) Describe the structure and function of desmosomes (and hemidesmosomes). - Desmosomes: Structurally similar to AJs but contain specialized cadherins that link to intermediate filaments instead of actin filaments. - Function- Provide mechanical strength - Hemidesmosomes: Firmly attaches epithelial cells to underlying cells to underlying basement membrane by connecting cell's internal keratin intermediate filaments to extracellular matrix proteins (anchor acting) to maintain tissue integrity.  7\. (pgs. 1117-1120, figs. 19-18, 19-19, 19-20, and 19-21) Describe the polarity of epithelial cells. Describe tight junctions at the molecular level and include claudins and occludins. - Epithelial cell polarity: Distinct membrane domains→ basal lamina and apical end. - Tight junctions: Cell-cell junction that seals adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other. - Claudins- Major transmembrane proteins forming tight junctions. - Occludins- Help maintain stability of tight junctions. A diagram of glucose level Description automatically generated  8\. (pgs. 1120-1121, fig. 19-22) Describe the use of scaffold proteins (include the PDZ domain) at the site of tight junctions. - PDZ domain- Often used as a docking site for intracellular tails of transmembrane proteins. - Zonula occludens (ZO): ZO-1, ZO-2, and ZO-3. - PDZ helps ZO occludens recognize and bind the C-terminal tails of specific partner proteins. One domain can attach to a claudin protein while other can attach to occludin/actin cytoskeleton. Scaffold proteins can assemble a meshwork of intracellular proteins that organizes and positions the sealing strands of tight junctions. A diagram of different types of protein Description automatically generated **Figure 19-22: Scaffold proteins at the tight junction.** 9\. (pgs. 1121-1113, figs. 19-23, 19-25, and 19-26) Describe the structure and function of gap junctions. What are the subunits? What can typically move through a gap junction? Can an action potential occur through gap junctions? What influences whether they are open or closed? - Gap junctions: Communicating channel-forming cell-cell junction present in most animal tissues that allows ions and small molecules to pass from the cytoplasm of one cell to the cytoplasm of the next. - Connexins- Four-pass transmembrane protein. Six connexins assemble in the plasma membrane to form a connexon or "hemichannel". - Connexon- Water-filled pore in plasma membrane formed by a ring of six connexin protein subunits. Half of a gap junction: connexons from 2 adjoining cells join to form a continuous channel through which ions and small molecules can pass. - Secondary messengers, inorganic salts, sugar, amino acid, nucleotides, vitamins, and metabolites can move through. - Less than 1000 Daltons can pass. - Electrical coupling via gap junctions contain electrically excitable cells. Action potentials can spready readily from cell to cell without delay. - Open and close triggered by voltage difference between 2 connected cells, pH changes, and concentration of free Ca2+.  10\. (pgs. 1123-1124, fig. 19-27) Describe the structure and function of plasmodesmata. - Plasmodesmata- Plant equivalent of a gap junction. Directly connect the cytoplasm of adjacent cells. - Desmotubule- Narrow cylinder that runs through the center of aa plasmodesmata. It is continuous with elements of smooth ER in each connected cells. - Allows passage of molecules with a mass of less than 800 Daltons. A diagram of a cell membrane Description automatically generated **Figure 19-27: Plasmodesmata.** 11\. (pgs. 1125-1126, fig. 19-28) Describe the structure and function of selectins. How do selectins work with integrins with regards to white blood cell adhesion and migration? - Selectins- Mediate transient, Ca2+ dependent cell-cell adhesion in bloodstream. - Ex: WBC and endothelium of blood vessels. - Selectins on endothelial cells bind weakly to oligosaccharides on WBC so it becomes loosely attached and rolls along the vessel wall. WBC then activated a cell-surface integrin called LFA 1, which binds to a proteins called ICAM1 on the membrane of the endothelial cell. WBC adheres to the vessel wall and then crawls out of the vessel.  **Figure 19-28: Structure and function of selectins.** 12\. (pgs. 1126-1127, fig. 19-29) Describe the function of the Ig superfamily, and more specifically ICAMs and NCAMs. - Ig Superfamily- Involved in cell-cell interactions/antigen recognition. - ICAMs- Regulate and migration of leukocytes (WBC) to endothelial cells particularly during inflammatory responses. - NCAMs- Cell adhesion proteins in the nervous system. Play a role in developmental processes such as neuronal migration, neurite outgrowth, synapse formation, and contributing to brain plasticity associated w/learning and memory by regulating cell-cell interactions through homophilic binding. A diagram of different types of dna Description automatically generated **Figure 19-29: Membranes of the Ig superfamily of cell-cell adhesion.** 13\. (pgs. 1127-1129, figs. 19-30 and 10-31) Generally, describe the extracellular matrix (ECM), how does it vary in form and function? ECM macromolecules are secreted by what type of cell? What are the three classes of ECM macromolecules? - ECM: Composed of many different proteins and polysaccharides that are secreted locally and assembled into an organized meshwork in close association w/surfaces of cells that produce them. - Fibroblast secret ECM macromolecules. - Classes of ECM macromolecules: - Glycosaminoglycans (GAGs)- Large and highly charged polysaccharides that are usually covalently linked to protein in form of proteoglycans. - Proteoglycans- Fibrous proteins that are primarily members of the collagen family. - Glycoproteins- Carry conventional asparagine-linked oligosaccharides.  14\. (pgs. 1129-1130, figs. 19-32, 19-33, and 19-34) Describe the structure and function of GAGs. Are they hydrophilic or hydrophobic (hint: do they have a net charge)? Describe hyaluronan. - GAGs- Long, linear, highly negatively charged polysaccharide composed of a repeating pair of sugars, one of which is always an amino sugar. Mainly found covalently linked to a protein core in extracellular matrix proteoglycans. - Ex: Chondroitin sulfate and dermatan sulfate, hyaluronan, heparin and heparan sulfate, keratan sulfate. - Hyaluronan- Type of non-sulfated GAG w/a regular repeating sequence of up to 25,000 identical disaccharide units and not linked to a core protein. Found in fluid lubricating joints and in many other tissues.  **Figure 19-32** 15\. (pgs. 1130-1132, figs. 19-35, 19-36, and 19-37) Describe the structure and function of proteoglycans. What are and aggrecan and decorin? - Proteoglycans- Molecule consisting of one or more GAG chains attached covalently to a core proteins. Acting like a "toothbrush" structure. - Polysaccharide chains assembles in Golgi before delivery to exterior of cell by exocytosis. A special linkage tetrasaccharide is attached to a serine side chain on the core protein to serve as a primer for polysaccharide growth. One sugar at a time is added by specific glycosyl transferase. - Sulfation increases negative charge and epimerization (alters configuration of substituents around individual carbon atoms in the sugar molecule). - Best-characterized membrane proteoglycan= syndecans (interact w/actin cytoskeleton and signaling molecules in cell cortex).  **Figure 19-35: Linkage between a GAG chain and its core protein in** **a proteoglycan molecule.** 16\. (pgs. 1132-1133, figs. 19-38 and 19-39, Table 19-2) Describe the structure and function of collagen. What accounts for the variation in collagen fibers? Be familiar with table 19-2 (don't memorize it). - Collagen- Fibrous protein rich in glycine and proline that is a major components of the ECM conferring tensile strength. - Long, stiff, triple-stranded helical structure, in which 3 collagen polypeptide chains, called αchains, are wound around one another (rope like) - Fibrillar collagens: Long rope-like structure w/few or no interruptions and which assemble into collagen fibrils. - Type 1 - Collagen fibrils: Higher-order collagen polymer of fibrillar collagens that assemble into thin structures many hundreds of micrometers long in mature tissues. - Fibril-associated collagens- Decorate surface of collagen fibrils. Thought to link to one another and to other components in ECM. - Type 6 and 7 - Networking-forming collagens- Basal lamina - Type 8 and 9 - Anchoring fibrils- Attach basal lamina of multilayered epithelia abundant in the skin. (Type 9)  17\. (pgs. 1133-1135, figs. 19-40 and 19-41) Where are collagen mRNAs translated? Describe what selected prolines and lysines are modified into. What disease will occur if proline hydroxylation does not occur? Describe the process where procollagen is modified and ultimately participates in the functional ECM. - Collagen mRNA translated→ Cytoplasm (interact w/ribosomes) - In the lumen of the ER selected prolines and lysines are hydroxylated to form hydroxyproline and hydroxylysine. - Some hydroxylysine are glycosylated - If proline hydroxylation does not occur→ Scurvy (vit. C deficiency): Loss of preexisting normal collagen in matrix. Blood vessels become fragile, teeth become loose, and wounds cease to heal. - Propeptides of the fibrillar procollagen molecules are removed by specific proteolytic enzymes outside the cell therefore converting procollagen to collagen. They then assemble in the extracellular space to form much larger collagen fibrils. - Propeptides function: 1) Guide intracellular formation of 3-stranded collagen molecules. 2) Retained until after secretion preventing intracellular formation of larger collagen fibrils that could be catastrophic for the cell. A diagram of a structure Description automatically generated **Figure 19-41: Cross-links formed between modified lysine side chains w/in a collagen fibril.** 18\. (pgs. 1135-1136, figs. 19-42, and 19-43) Describe the variation in collagen organization. What helps to organize collagen into these patterns? - Types of variation: - Mammals- Woven in wickerwork pattern to resist tensile stress in multiple directions - Tendons- Parallel bundles. - Mature bone and cornea- Orderly plywoodlike layers (lying parallel but nearly @ right angles to fibrils in layers on either side). - Connective-tissue cells determine size and arrangement. - Fibril-associated collagens- Has a flexible 3-stranded helical structure and binds to surface of collagen fibrils. Mediates interaction of collagen fibrils w/one another and w/other matrix macromolecules to help determine their organization. - Includes type IX and XII  19\. (pgs. 1136-1137, figs. 19-44 and 19-45) Describe the structure and function of elastin. What is it secreted as? What are fibrillin? - Elastin: Extracellular protein that forms extensible fibers in connective tissue. - Contains proline and glycine but aren't glycosylated. - Allows for stretch and shrinking. - Tropoelastin is secreted into the extracellular space and assembled into elastic fibers close to plasma membrane. Become highly cross-linked to one another ( extensive network of elastin fibers and sheets). - Fibrillin- Binds elastin and is essential for integrity of elastic fibers. - Diseases: Marfan syndrome (severe- aorta rupture), displacement of lens and abnormalities of the skeleton and joints. A diagram of a stretch and stretch Description automatically generated **Figure 19-45: Stretching a network of elastin molecules.** 20\. (1138-1141, figs. 19-47, 19-48, 19-49, and 19-50) Describe the structure and function of fibronectin. What is an RGD sequence? How and where are fibronectins assembled - what influences this assembly? - Fibronectin- Extracellular matrix protein involved in adhesion of cells to the matrix and guidance of migrating cells during embryogenesis. Integrins on the cell surface are receptors for fibronectin. - Type III fibronectin repeat: Major repeating domains (90 amino acids and occurs at least 15X in each subunit). - RDG sequence- Tripeptide sequence of arginine-glycine-aspartic acid that forms a binding site for integrins; present in fibronectin and some other extracellular proteins. - Fibronectins assemble into fibrils only on where cells posses appropriate fibronectin-binding proteins- particular integrins. These provide linkage from fibronectin outside cell to actin cytoskeleton inside it. - Influences and dependent on tension to ensure fibronectin fibrils assemble where there is a mechanical need for them. - Type III fibronectin repeat A diagram of different types of dna Description automatically generated **Figure 19-47: Complex glycoproteins of extracellular matrix.**  **Figure 19-49: Tension-sensing by fibronectin.** 21\. (pg. 1141, fig. 19-51) Describe the basic structure and function of the basal lamina. Describe the three ways in which it is organized. - Basal lamina: Thin mat of extracellular matrix that separates epithelial sheet, and many other types of cells such as muscle/fat cells, from connective tissue. - Able to determine cell polarity, influence metabolism, organize proteins in adjacent plasma membrane, promote cell survival, proliferation/differentiation, and serve as highways for cell migration. - 3 ways of organization: Surrounding cells, lying underneath sheets of epithelial cells, or separate two sheet of different cell types. A diagram of lumen and lumen Description automatically generated **Figure 19-51: 3 ways basal lamina is organized.** 22\. (pgs. 1141-1144, figs. 19-52, 19-53, 19-54, and 19-55) What cells synthesize the basal lamina? What are the basic components? Describe the structures and functions of lamina and type IV collagen. List the diverse functions of the basil lamina. - Synthesize by cells on each side of it: epithelia contribute one set of basal lamina components while cells of underlying bed of connective tissue (stroma) contribute another set. - Basic components: Glycoproteins laminin, type IV collagen, and nidogen, proteoglycan perlecan, fibronectin, and type XVIII collagen. - Laminin- Extracellular matrix fibrous protein found in basal laminae forming a sheetlike network. - Type IV collagen- Essential component of mature basal laminae consisting of 3 long protein chains twisted into a rope-like superhelix w/multiple bends. Separate molecules assemble into a flexible, felt-like network that gives the basal lamina tensile strength. - Functions: Selective barrier to movement of cells (filter like) and important in tissue regeneration (neuromuscular junction)  **Figure 19-53: Structure of laminin** A diagram of a complex structure Description automatically generated **Figure 19-54: Model of molecular structure of a basal lamina.** 23\. (pgs. 1144-1145) Describe the importance for the ability to rapidly degrade the ECM. What are the functions of metalloproteases and serine proteases? - Rapid degradation ECM is required when repairing tissue. The ability to cut through helps in two ways: enables them to divide while embedded in matrix and enables them to travel through. W/out the enzyme needed to degrade surrounding matrix it is inhibited from dividing and hindered from migration. - Matrix metalloprotease- Ca2+ or Zn2+ dependent proteolytic enzyme present in the extracellular matrix that degrades matrix proteins (Including collagenases). - Serine proteases- Type of protease that has a reactive serine in the active site. 24\. (pgs. 1147-111-48, figs. 19-56 and 19-57) Describe the basic structure and function of integrins. Identify the components associated with the integrins in figures 19-56 and 19-57. - Integrins: Can transmit signals in both directions across the plasma membrane. When tension is applied it can cause an integrin to tighten its grip on intracellular and extracellular structures and loss of tension can loosen its hold. Molecular signaling complexes fall apart on either side of the membrane if grip is loosened. - Composed of two noncovalently associated glycoprotein subunits called α and β. - Help span cell membrane and have short intracellular C-terminal tails and large N-terminal extracellular domains. - Figure 19-56: Kindlin (bind at another site on the tail), talin (large adopter protein involved in linkage), vinculin (helps reinforce and regulate linkage of actin filaments) **Figure 19-56: Subunit structure of an active integrin molecule, linking extracellular matrix to the actin cytoskeleton.** 25\. (pgs. 1149-1151, fig. 19-58 and 19-59) Describe how integrins are activated and inactivated. Why do integrins tend to cluster? - Inactive: External segment of integrin dimer are folded together into a compact structure that binds poorly to matrix proteins. - Cytoplasmic tails of dimer are hooked together preventing their interaction w/cytoskeletal linker proteins. - Active: Two integrin subunits unhooked at the membrane to expose the intracellular binding sites for cytoplasmic adaptor proteins and external domains unfold and extend to expose a high-affinity matrix-binding site at tips of subunit. - Tendency to cluster→ After activation to form a dense plaque in which many integrin molecules are anchored to cytoskeletal filaments. This forms a strong and effective bond with ECM molecules.  **Figure 19-58: Two major activity states.** A diagram of a path Description automatically generated **Figure 19-59: Activation of integrins by intracellular signaling.** 26\. (pgs. 1151-1152) Describe the concept of anchorage dependence. How could the loss of this contribute to cancer? - Anchorage dependence- Dependence of cell growth, proliferation, and survival on attachment to a substratum. - Mutation/override allow cells to escape from anchorage dependence and occur in cancer cells (invasive behavior). 27\. (pgs. 1153-1154, fig. 19-61) Describe how the talin protein acts as a tension sensor. - Talin: Undergoes conformational changes in response to mechanical force, specifically by unfolding its rod domain which exposes binding sites for other proteins like vinculin. - Binds to one type of integrin α subunit.  Figure 19-61: Talin= Tension sensor 28\. (pgs. 1154-156, fig. 19-62) Describe the basic components and functions of a plant cell wall. How is high turgor pressure achieved and why is it important. - Plant cell wall: - Primary cell wall- First cell wall produced by a developing plant cell; thin and flexible allowing room for cell growth. - Secondary cell wall- Permanent rigid cell wall that is laid down underneath the thin primary cell wall in certain plant cells that have completed their growth. - Lignin- Network of cross-linked phenolic compounds that forms a supporting network throughout the cells walls of xylem and woody tissue in plants. - Turgor pressure: Large hydrostatic pressure developed inside a plant cell as the result of the intake of water by osmosis; it is the force driving cell expansion in plant growth and it maintains rigidity of plant stems and leaves. 29\. (pgs. 1156-1157, figs. 19-63 and 19-64) Describe the structure of cellulose. How are cellulose, cross-linking glycans, and pectin arranged in the plant primary cell wall? - Cellulose: Long, unbranched chains of glucose; major constituent of plant cell walls. - Cellulose microfibrils- Highly ordered crystalline aggregate formed from bundles of about 18 cellulose chains, arranged w/same polarity and stuck together in overlapping parallel arrays by H bonds between adjacent cellulose molecules. - Cross-linking glycans- One of a heterogeneous group of branched polysaccharides that help to cross-link cellulose microfibrils into a complex network. Has a long linear backbone of one sugar type (glucose, xylose, mannose) w/short side chains of other sugars. - Pectins- Mixture of polysaccharides rich in galacturonic acid that forms a highly hydrated matrix in which cellulose is embedded in plant cell walls. A diagram of a molecule Description automatically generated **Figure 19-63: Cellulose**.  **Figure 19-64: Portion of a primary plant cell wall showing two major polysaccharide networks.** 30\. (pgs. 1157-1159, figs. 19-65 and 19-66) Describe how the orientation of cellulose microfibrils influences the direction of cell elongation. Understand the cellulose synthesis can be spatially constrained by cortical microtubules. - Cellulose microfibrils are unable to stretch and therefore the orientation in the innermost layers of wall govern direction in which the cell expands. Cells in plants can anticipate their future morphology by controlling orientation of cellulose microfibrils that they deposit in the wall. - Preexisting orientation of microfibrils can be propagated even in absence of microtubules but any change in deposition of cellulose microfibrils requires that intact microtubules be present to determine the new orientation.