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BSC 300, Week 9

by: Ashley Bartolomeo

BSC 300, Week 9 BSC 300

Ashley Bartolomeo
GPA 3.9

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Notes on first half of chapter 7
Cell biology
Dr. Jenny
Class Notes
Cell, Biology
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This 4 page Class Notes was uploaded by Ashley Bartolomeo on Tuesday October 11, 2016. The Class Notes belongs to BSC 300 at University of Alabama - Tuscaloosa taught by Dr. Jenny in Fall. Since its upload, it has received 2 views. For similar materials see Cell biology in Biology at University of Alabama - Tuscaloosa.


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Date Created: 10/11/16
Chapter 7 Interactions Between Cells and Their Environment Key Concepts  Define structure and function of glycocalyx and extracellular matrix  Describe function and structure of basement membranes (basal lamina)  Describe structures of components of the extracellular matrix (collagen, GAGs, proteoglycans, glycoproteins) and differentiate between them  Clarify the steps involved in the adhesion of cells to a non-cellular surface  Membrane proteins involved in adhesion of cells to non-cellular surfaces  Describe the structures and functions of the different cell junctions  Describe the membrane proteins involved in cell-cell adhesion Cells Function Cooperatively to Generate Tissues  Cells interact physically and chemically with one another and extracellular material to form defined tissues  Epithelial are sheets of closely packed cells tightly connected to one another and a define extracellular material, the basement membrane  Form a protective barrier that line both the external surface and internal cavities and lumina of tissues  Example, the epidermal layer of skin  Connective tissues consist mostly of extracellular material secreted by the resident cells  The cells, referred to generally as fibroblasts, are largely autonomous, non-connected and motile  Examples include the dermis of skin and cartilage  The other two major tissue types are muscle and neuronal The Extracellular Space  The glycocalyx (cell coat) is a glycoprotein-polysaccharide covering that surrounds the cell membranes of epithelial cells  Glycocaly mediates cell-cell and cell-substratum and provides mechanical protection to cells and inhibits movement of extracellular material toward the plasma membrane  It also helps facilitate the binding of important signaling molecule to the cell surface  Extracellular matrix (ECM): an organized network beyond the plasma membrane that plays key regulatory roles in determining cell shape and activities. Extensively involved in cell signaling as it regulates diffusion of ligands and their interactions with receptors  Unique composition of fibrous proteins and proteoglycans are secreted by and surround all cell types and this ECM is involved in regulating diverse cellular physiology including cell-cell contact, proliferation, migration, cell signaling, gene expression and differentiation The Basement Membrane  Basement membrane (aka basal lamina), specialized ECM under the basal surface of epithelia. A continuous sheet that: o Maintains cell attachment o Provide signals for cell survival (survival of most cells is contact dependent) o Separate distinct tissues within an organ o Serves as substratum for cell migration o Forms a barrier to macromolecules Organization of the ECM  Though distinct for each tissue the ECM is generally composed of: o Long fibrous proteins that form a mesh like network surrounding the cell o Highly glycosylated proteoglycans that cushion the cell o Transmembrane proteins that are interconnected to these extracellular molecules and respond to both mechanical and chemical signals The Structure of Collagen I  Collagens: fibrous glycoproteins found only in the ECM o Most abundant proteins in the human body o Provide high tensile strength o Diverse family: ~27 distinct types encoded by human genome o Each is restricted to a particular tissue o Secreted principally by fibroblasts (also smooth muscle and epithelial) o Collagen molecule: triple helix of three helical alpha chains bundled together to form large collagen bundles Collagen  Collagens establish an insoluble framework that determines the mechanical properties of the matrix  Prolines and lysines are heavily hydroxylated by specific enzymes allowing crosslinking via H-bonds stabilizing the trimer  Several collagen types (like collagen I, bottom) assemble into long, rigid cable-like fibrils, strengthened by covalent crosslinks between lysines  ECM contains heterogeneous mix of different collagens and trimers can be homo- or hetertrimeric, producing incredible diversity in functional properties  Different structural arrangements contribute uniquely to functional properties  Tendon collagen is aligned parallel to the long axis of the tendon to give tensile strength in the direction of pulling forces  In the cornea stratified, perpendicular layers provide rigidity and structural protection, while uniformity in size and distribution minimizes scattering of incoming light  Diverse connective tissue diseases result from improper collagen formation  For example, scurvy, resulting from vitamin C deficiency (ascorbic acid) prevents proline hydroxylation and collagen processing  This leads to poor wound healing, inflamed gums, tooth loss, brittle bones and damaged blood vessels  Not all collegans form fibrils: collagen type IV is non-fibrillar, and is restricted to the basement membrane Collagen Based Diseases  A common disease of many tissues is excessive production of collagen- containing connective tissue: known as fibrosis  Diverse causes to such collagen containing scar tissue that replaces normal connective tissue include pulmonary fibrosis and cirrhosis of the liver  Collagen mutations result in a number of human disorders o Type I (osteogenesis imperfecta – fragile bones) o Type II (dwarfism: spondyleopiphyseal dysplasia) o Diverse collagens: Ehler-Danlos syndromes (hyperflexibilty)  Non-fibrillar (type IV) o Alpert syndrome – kidney disease of the glomerular basement membrane Structure of a Proteoglycan Complex  Proteoglycans: protein-polysaccharide complexes, with a core protein attached to long chain glycosaminoglycans (GAGs) o Each GAG chain consist of a repeating disaccharide structure o Extremely acidic due to presence of both sulfate and carboxyl groups o Negatively charged GAGs attract lots of cations, which in turn attract water forming a porous, hydrated gel – providing a cushion of support in connective tissues o Often taken as supplements for improving skin and joint conditions o In the ECM proteoglycans are cross-linked to a nonsulfated GAG, hyaluronic acid forming a giant complex o Resists crushing forces; cushion cells o Provide binding sites for growth hormones to protect from proteases o Regulate diffusion of small signaling molecules in developing embryo Fibronectin  Fibronectin: facilities interactions between ECM components  Each fibronectin contains about 30 distinct FN globular modules arranged in 5-6 functional domains  Single human gene produces several protein isoforms through alternative splicing  Each fibronectin protein is a dimer of two polypeptides covalently joined by disulfide bridges  Each domain provides unique interaction sites for diverse extracellular and integral membrane (IM) proteins  1. Collagen, proteoglycans and other fibronectin proteins enhance framework of the ECM  2. IM receptors proteins called integrins gold the ECM in stable attachment to the cell  Fibronectin transmits mechanical force as signals to attached cells which elay this info to the cell interior for responses via the integrin receptors Cell Migration During Embryogenesis  Fibronectin and another ECM protein laminin play essential roles as road maps for migrating cells during animal development  Specific fibronectin and laminin proteins are recognized by receptor proteins on migrating cell surfaces and followed to the appropriate destination  Examples include migrating neural crest cells that differentiate as pigment cells and facial bone/ cartilage that follow fibronectin tracks, and migrating primordial germ cells that migrate along tracks of laminin from the dorsal mesentery to the gonad primordia Dynamic Properties of the ECM  Not static, constant remodeling by degradation and reconstruction  ECM materials degraded by matrix metalloproteinases (MMPs) secreted by migrating fibroblast cells  MMPs promote tissue remodeling during embryogenesis, embryonic cell migration, wound healing and blood vessel formation  Disease state associated with MMPs o Arthritis, blood clots, tooth and gum disease, heart attacks o Malignant tumor cells acquire MMP expression, allowing invasion (metastasis) into other tissues


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