Chapter 20 Flashcards
What is the ECM?
Extracellular matrix, structural component of tissues that influences their development and physiology
What is the ECM made of (3)?
Structural components (collagen), adhesive glycoproteins (fibronectins), and matrix components (proteoglycans)
What are the cells that live in the ECM?
connective tissue cells both inhabit and manufacture the ECM, and are called fibroblasts or osteoblasts (bone)
In general, how are macromolecules added to the ECM?
synthesized internally, secreted by exocytosis, assemble into huge, cohesive aggregates
Describe connective tissue?
tissues such as bone, tendons, and the dermis of the skin, in which ECM makes up the bulk of the tissue and carries the mechanical load
Describe bone vs cartilage vs connective tissue
bone β hard and dense
cartilage β resilient and shock absorbing
connective tissue β flexible
Define collagen
a helical triple-stranded fibrous protein that is a major component of the ECM and connective tissues
Describe the structure of collagen (base unit β structure in tissues)
three collagen polypeptides wind around each other to form a ropelike superhelix
some of these assemble into fibrils, which can then pack into collagen fibers that are arranged both longitudinally and in a cross section
How is collagen produced? What modifications are made?
Fibroblasts/Osteoblasts produce collagen molecules in a precursor form called procollagen with additional peptide extensions that prevent premature assembly
Extracellular enzymes called procollagen proteinases cut off the terminal extensions to allow assemble once in the extracellular space
What is the purpose of collagen?
Provides tensile strength to resist stretching
Define fibronectin
Extracellular matrix protein that helps cells attach to the matrix by acting as a linker, binding a cell-surface integrin molecule on one end and a matrix component (e.g collagen) on the other
Describe the structure of fibronectin
Made of two polypeptides that are covalently bonded through disulfide bonds at their C-terminus
Define integrins and describe their structure
Family of transmembrane proteins present on cell surfaces that enable cells to make/break connections to the ECM, allowing them to crawl through a tissue
Made of two heterodimers, πͺ and π·
Describe how integins are used in cell crawling. Include what their extracellular domain and intracellular domains bind to.
Cells can grab the ECM at their front end (focal adhesions or focal contacts) and release at the back end
Extracellular domain binds to fibronectin, intracellular domain binds to actin filaments
What is the secondary role of integrins? (not cell crawling)
Also involved in signaling to cells when bound to ECM and responding from signals inside the cell, allowing them to change their adhesion to the ECM
Define GAGs. What are they used for (when alone)?
GAGs (glycosaminoglycans) are polysaccharide chains that form a space filling gel in the ECM of connective tissue by attracting ions (and therefore water)
Help animal tissues resist compression and is tough and resilient
Define proteoglycans
Molecules that have one or more GAG chains attached to a glycosylated core protein
What are proteoglycans used for?
Aggregates can form gels that regulate the passage of molecules through the ECM and guide cell migration
What is the basal lamina? What is its major/general purpose?
Thin, tough sheet of ECM secreted by epithelial cells, upon which the cells sit
Barrier between epithelial cells and connective tissue
What is the basal lamina composed of? What are their roles?
Composed mainly of collagen and a protein called laminin
Laminin provides adhesive sites for integrin molecules in the basal plasma membranes of epithelial cells, and therefore serves a linking role similar to that of fibronectin
Define epitheium
a sheet of cells covering an external surface or lining an internal body cavity creating a barrier between the tissue and the outside
What is the general and specific role of tight junctions?
Hold cells together
Prevent the movement of water-soluble molecules and membrane proteins
What are tight junctions made of?
Formed by claudins and occludins arranged in strands
What is the general and specific role of adherens junctions?
Hold cells together
May form a continuous adhesion belt, connecting bundles of actin filaments from cell to cell
What are adherens junctions made of?
Actin filaments tethered to many cadherin molecules
What is the general and specific role of desmosome junctions?
Hold cells together
Join ropelike filaments of kerain (IFs) of adjoining cells by cadherin
Describe keratin
a type of intermediate filament that provides tensile strength in epithelial cells
What is the general role of hemidesmosomes?
Anchor epithelial cells to basal lamina
What are hemidesmosomes made of?
Extracellular domains of integrins bind to laminin, intracellular domains bind to keratin (IF)
Describe the βplaquesβ in desmosomes and hemidesmosomes
Both desmosomes and hemidesmosomes have electron-dense protein plaques between the keratin filaments and the cell membrane
What is the general and specific role of gap junctions?
Hold cells together
Allows ions and small molecules to move directly from the cytosol of one cell to that of another, creating an electrical and metabolic coupling
What are gap junctions made of?
Gap between cells is spanned by transmembrane protein connexons that lie in the plasma membrane of two apposed cells and are aligned end-to-end to form narrow, water-filled channels
Define cadherin
Ca+2 dependent protein
Mediate the attachment of one cell to another in animal tissues in both adherens junctions and desmosomes
How to cadherins work?
Cadherin molecule in the plasma membrane of one cell binds directly to an identical cadherin molecule in the plasma membrane of its neighbor
