BIO 127 Module 3.pdf

3A. EXTRACELLULAR MATRIX Tissue o an organized assembly of cells, held together by cell-to-cell adhesion, ECM, or both 2. Network Materials Surrounding Collagen Fiber Extracellular matrix (ECM)...

3A. EXTRACELLULAR MATRIX Tissue o an organized assembly of cells, held together by cell-to-cell adhesion, ECM, or both 2. Network Materials Surrounding Collagen Fiber Extracellular matrix (ECM) o hold cells and tissues together highly diversified group of proteoglycans and o organized lattice within which cells can glycoproteins migrate and interact with one another proteoglycans o linear polypeptide chain to which ECM of Animal Cells carbohydrate chains are linked via ser, thr, and asn ▪ 1 to 200 diff types of CHO’s → Secreted by the cell and basically surrounds diff types of proteoglycans tissues High amount in connective tissues where cells are sparsely distributed Components: o primary fibers o network materials surrounding collagen fibers o linker molecules 1. Primary Fibers (Collagen) insoluble glycoprotein o glucose + galactose Examples: o 10% of collagen’s total weight o high glycine and modified aa Chondroitin sulfate cartilage, skin (hydroxylysine and hydroxyproline) Keratan sulfate bones, cornea tendons, fibrillar CT, skin, individual collagen molecule Dermatan sulfate cornea o linear α-chain Heparan sulfate cornea, nerve fibers o 3 α- chains twisted together Hyaluronic acid- o triple helix cartilage, bone, tendon, proteoglycan aorta, smooth muscles complex 1  the consistency of ECM depends on the type Laminins and combination of collagen and proteoglycan: o ↑ proteoglycan ▪ relatively soft ECM (as in conserved from simple invertebrates to humans cartilage) bind cells to the basal lamina o pure collagen fibers three large polypeptides (α, β, and γ) joined by ▪ tough and elastic (as in tedons) disulfide bonds into a crosslinked structure o proteoglycans + hydroxyapatite + a portion of the long arm: three-stranded coil CaCO3 + citrate domains for binding of cell surface receptors, ▪ hard (as in bones) collagen, laminin and proteoglycans 3. Linker Molecules connect collagen and proteoglycans in the ECM with each other and with the Pm fibronectin and laminin o adhesive glycoproteins o domains as binding sites for proteoglycans, collagen, and cell surface receptors ECM proteins accumulate adjacent to particular target tissues in the developing animal by a variety of mechanisms: o local synthesis in the target tissue o local synthesis by migrating cells o secretion from a distant source and capture by the target tissue Fibronectin assembly of ECMs at discrete sites in the developing animal: occur widely throughout supporting tissues and body fluids two nearly identical polypeptide chains two disulfide bonds multiple domains as binding sites for proteoglycans, collagen and cell surface receptors o accumulation could be receptor independent (left side of each tissue) or receptor dependent (right side of each tissue) o capture requires interaction with a protein localized on the target tissue, either another ECM protein (left side of tissue) or receptor (right side) 2  ECM and Development ECM of Plants Cells the composition of the ECM changes as CW components: development progresses o plants and fungi: cellular microfibrils certain ECM components are restricted in their embedded in matrix of polysaccharides expression to certain developing tissues and proteins cell interaction w/ ECM is required to prolong o bacteria: mainly peptidoglycan the signaling by other pathways → cell o archaea: diverse composition differentiation CW functions: o cell rigidity o permeability barrier o protection against physical damage and infection Cell Wall Components cellulose o glucose-based polysaccharide o provides tensile strength in plant cells, like IF hemocellulose & extensins o polysaccharide and glycoprotein o link microfibrils together to form network in animals a. providing a road for cell migration b. inhibition of lateral protrusions during convergent extensions c. integrin switching during migration of the distal tip cell d. providing a morphogenic checkpoint for tissue differentiation e. specifying the orientation of cell divisions f. modulation of morphogen gradients g. insulation to avoid nonspecific sticking betw tissues pectin h. mediating adhesion betw tissue layers o polysaccharide i. generating lumens w/in tissues o forms matrix where microfibrils are embedded o for compression resistance o for cell-to-cell adhesion (lamella) lignin o complex organic polymer o found specifically in woody tissue o enhances rigidity and makes tissue waterproof 3  Cell Wall primary CW o relatively thin wall formed during cell division o cellulose microfibrils in gel-like matrix Cell Wall and Development o allows cell expansion secondary CW o thicker and more rigid CW architecture is highly dynamic and o formed after cell growth substantially remodeled o usually has more cellulose o determine size and shape of cells o may also contain lignin for woody o contribute to functional specialization plants of tissues and organs CW serve as a reservoir of latent signal molecules (oligosaccharide fragments) plasmodesmata o unique feature of plant CW o membrane-bound cytoplasmic bridges passing through the CW o allows passage of water and small solutes, some proteins and regulatory RNA o makes cytoplasm continuous in adjacent cells o basis for Supracellularity Hypothesis ▪ cells would aggregate w/ e/o 4  3B. CELL JUNCTION 1. Occluding Junctions seal between epithelial cells 1a. Tight Junctions Occluding tight junctions (vertebrates) junctions septate junctions (invertebrates) zonulae occludens (singular zonula) gap junctions Communicating chemical synapses anastomosing network of protein strands junctions connecting the outer leaflets of the two plasmodesmata (plants) AF attachment site interacting PM adherens junctions encircle apical end of each cell in the epithelial Anchoring focal adhesions sheet junctions IF attachment site desmosomes hemi-desmosomes Intercellular Junctions in Animals Proteins Involved in Tight Junctions Occludin o important in tight junction stability and barrier function Claudin o determines the barrier properties of cell to cell contact existing between sealed PMs ZO (zonulae occludens) proteins o scaffolding proteins o provide the structural basis for the assembly of multiprotein complexes at the cytoplasmic surface of intercellular junctions Cingulin o involved in regulating gene expressions or behavior of endothelial or epithelial cells JAM (junctional adhesion molecules) o mediates interaction between two cells Cadherins o mediate cell–cell adhesion in animals o regulate contact formation and stability o play a crucial role in tissue morphogenesis and homeostasis 5  e.g. transcellular transport of glucose at the apical domain o Na+-driven glucose symport actively transport glucose into the epithelial cell at the basolateral domain o glucose carriers mediate facilitated diffusion of glucose from the cell to the extracellular fluid maintain directional transport of glucose Na+- glucose symport must not be allowed to migrate to the basolateral surface of the cell Functions of Tight Junctions 1. seal neighboring cells together so that water- soluble molecules cannot leak between the cells o epithelia of intestine and urinary bladder o allow epithelia to serve as barriers to solute diffusion 2. confine transport proteins to their appropriate membrane domains 6  1b. Septate Junctions arranged in parallel rows with regular periodicity main occluding junction in invertebrate tissues co-exist with adhesion belts form continuous band around the apical borders of epithelial cells serve as sites of attachment for actin filaments o help hold cells together connexons o protrude from cell surface o hold the interacting plasma membrane at a fixed distance o homomeric: same type of connexins o heteromeric: diff type of connexins impact of type of connexons: o differences in permeability and selectivity for diff molecules and ions most connexin disorders are autosomal dominant close: ↑ [Ca2+] and ↓ pH of the cytosol Functions of Gap Junctions 2. Comomunicating Junctions 1. cell-cell communication o pore size ~1.5 nm o for molecules