Connections and the Extracellular Matrix - Cell Biology 4 Flashcards
Tissues
Multiple cell types organised into coopoeratice assemblies performing particular jobs and with unique functional architectures
Cell-cell and cell-extracellular matrix interactions
Critical for assembling cells into tissues, controlling cell shaoe and function and determining the developmental fate of cells and tissues (differentiating into particular cell types)
Molecules involved in determining shape and function of cells
Cell-adhesion molecules (CAMs), adhesion receptors and Extra cellular matric (ECM)
Cell-adhesion molecules
mediate direct cell-cell adhesions
Adhesion receptors
Mediate interactions between cells and matric
Extracellular Matrix (ECM)
Dynamic meshwork of proteins and polysaccharides in tissues of plants and animals. It shapes their cells from the outside.
Cell wall
Type of extracellular matric in plants that encloses, protects and shapes plant cells on the extracellular side of the plasma membrane
Cell wall main carbohydrate components
Cellulose and pectin
Cellulose
Tough, water impermeable carbohydrate polymer (glucose) providing plant cell wall structure.
Plant cell wall strcture
Cellulose, other polysaccharides form and structural proteins form a structure that resists compression and tension (high tensile strength)
Lignin
Polymer deposited in cellulose matrix that adds rigidity and waterproofing to wood.
Primary cell wall
Cell wall in all plants just outside of the extracellular mebrane which expans in response to change in water pressure and as the plant grows
Secondary cell wall
Deposited once plants are finished growing. More rigid and often reinforced by compounds like lignin, making wood.
Ceullulose sythesis
Synthesised on surface of cell by cellulose synthase (embedded in the membrane) unlike most extracellular componentswhich are secreted by exocytosis
Microtubules
Cytoskeletal components guiding intracellular structure arrangement via orientation of movement of cellulose synthase complex. So cellulose is deposited in correct direction.
Cell Junctions
Structures facilitating communication and adhesion between cells.
Adhesion Receptors
Proteins mediating cell-matrix adhesion interactions.
Cytoskeleton
Network providing structural support and cell shape.
Cellulose Synthase
Enzyme synthesizing cellulose on the cell surface.
Cellulose and tugor pressure
Orientation of cellulose microfibrils influences direction cell elongates under turgor pressure
Direction of elongation in plant cells
Perpendicular (at right angles) to orientation of microfibrils - their tensile strength only allow expansion in one direction.
Turgor Pressure
Internal water pressure influencing plant cell elongation which is uniform in all directions.
Determination of final shape of plant organ (eg shoot)
Direction in which its cells expans
Plasmodesmata
Channels connecting cytoplasm of adjacent plant cells allowing cell communication.
Desmotubule
Tubular structure derived from SER within plasmodesmata connecting cells. Allows solutes and other molecules to pass between 2 different plant cells
Intercytoplasmic channels of plasmodesmata
Pierce plant cell walls, connecting interiors of all cells in a plant
ECM in animals
Forms bulk of connective tissues (like cartilege, bones, tendons, dermis of skin and jelly filling the eyes). Prevents collapse
Production of ECM in animals
Secreted and deposited by some cells of connective tissues (fibroblasts and osteoblasts)
Fibroblasts
Cells producing ECM (mosrtly collagen) in connective tissues. These can differentiate into other cell types, especially during embryonic development.
Osteoblasts
Bone cells responsible for ECM production (minerals like calcium phosphate to strengthen bone).
Intermediate Filaments
Provide structural support within the cell.
Actin Filaments
Cytoskeletal elements forming membrane projections.
Proteoglycans
Component of animal ECM. Carbohydrates with protein components with charge residues (Hydrophillic), attracting water. Allows ECM to function like a gel.
Benefits of ECM functioning like a gel
Responds to compression (compresses a bit but not too much), providing support and cushioning joints.
Triple Helical Structure
Collagen’s unique structure formed by three polypeptides which interact via H-bonds intertwine, forming a superhelical structure
Collagen helices structure
Helices stabilised by steric repulsion of the proline (AA) rings. This means only one AA (GLYCINE) can fit in helix’s interior, spaved every 3 residues very precisely. This gives a striated appearance. s glycine is smallest AA, collagen is able to pack together closely
Collagen fibrils
Many rod-like collagen molecules are covalently cross-linked togethr in the extracellular space, further strengthening collagen and fomring fibrils
Organisation of collagen
Different in different tissues to fulfil specific needs.
E.g. in tendons in parallel bundles to respond to pulling force. In skin sheets are in different directions to resist tensile stress in different directions
Scurvy
Vitamin C deficiency causing bleeding and lethargy, haemorrhage under the skin and then death.
Integrins
Transmembrane proteins (cell adhesion molecules) that bind to actin cytoskeleton in sytoplasm and fibronectin which is connected to collagen.
Fibronectin
ECM protein binding collagen and integrins.
Transmission of tension across plasma membrane
Integrin is anchored inside the cell by adaptor proteins to actin cytoskeleton and externally via fibronectin to other extracellular matrix proteins (eg collagen fibril)
Epithelia
Majorty of cell types in multicellular organisms are joined side by sidem forming multicellular sheets = barrier covering body external surface and linining internal cavities
Two faces of epithelial sheets
Apical and basal
Apical face
Free surface of epithelial cells exposed outside (like gut cavity or air in lungs/mouth cavity)
Basal face
Surface of epithelial cells resting on connective tissue.
Basal lamina
Specialized ECM layer attached to epithelial cells
Polarisation of epithelia
Certain structures only exist at the apical or basal end, providing organisation related to function of particular epithelia.
Tight junctions
Seals neighboring epithelial cells to prevent leakage of molecules between them.
Claudins and Occludins
Proteins forming tight junction strands. arranged in strands along the junction
Desmosomes
Join intermediate filaments (keratin) in one cell to another for tensile strength so cells don’t rip apart under mechanical strength.
Cadherins
Protein family anchoring desmosomes and adherens junctions by nucleating cytoplasmic plaque
Adherens junctions
Link actin cytoskeleton between adjacent cells, allowing contractile movement. Anchored by cadherins
Contraction of actin filament
Via adherens junctions. Contraction causes the layer to roll = tube-like structures and even spheres. This is crucial for embryonic development.
Formation of epithelial tubes from sheets in gut
Contraction of apical bundles of actin filaments linked fron cell to cell via adherens junctions = cells contract at their apex. Depending on their orientation the epthelial sheet will invaginate or roll up into a tube (pinched off ad separated).
Gap junctions
Channels allowing direct intercellular communication. = passage of small ions and water molecules
Connexons
Protein assemblies (6 identical subunits) linking opposing plasma mebranes.
Two join across untercellular gap forming anqueous channel connecting cytosols of cells = gap junction channels.
Hemidesmosomes
Anchor intermediate filaments to basal lamina, similar structure to desmosomes.
Permeability of gap junctions
Can be regulated via extracellular signals like neurotransmitters
Hydra vulgaris
Simple organism with two epithelial layers (epidermis and gasyrodermins), one facing outside and one inside.
= diploblast. Only two embryonic layers (ecto and endo)
