Summary

This document discusses cell-to-cell adhesion, explaining the mechanisms and structures involved. It covers the extracellular matrix, types of protein fibers, and specialized cell junctions like desmosomes, tight junctions, and gap junctions.

Full Transcript

CELL TO CEL ADHENSION Friday, September 15, 2023 9:55 AM CELL TO CELL ADHENSIONS → Plasma membranes also participate in cell-to-cell adhesion → Cells are held together by three different means: ○ Cell Adhesion Molecules (CAMs) -> anchored to the membrane ○ The Extracellul...

CELL TO CEL ADHENSION Friday, September 15, 2023 9:55 AM CELL TO CELL ADHENSIONS → Plasma membranes also participate in cell-to-cell adhesion → Cells are held together by three different means: ○ Cell Adhesion Molecules (CAMs) -> anchored to the membrane ○ The Extracellular Molecules (ECMs) ○ Specialized cell junctions EXTRACELLUALR MATRIX → The ECM is an intricate network of fibrous proteins embedded in a watery, gel-like substance (A.k.a. interstitial fluid) composed of complex carbohydrates ○ The interstitial fluid provides a pathway for diffusion of nutrients, wastes, and other water-soluble traffic between the blood and tissue cells ○ It is the space and fluid between cells in the tissue ○ ECM is located on the outside of all cells THE 3 TYPES OF EXTRACELLULAR PROTEIN FIBERS → Collagen ○ Forms cable-like fibres ○ Tensile strength (most abundant protein in the body) § The strongest fiber we have ○ About 1/2 of total body protein by weight ○ Found in every cell ○ Can be found in skin, muscle, and bone and tissue ○ The type of tissue that produces scars → Elastin ○ Rubber-like protein fiber ○ Stretching and recoiling ○ Can be found in the lungs and heart → Fibronectin ○ Promotes cell adhesion ○ Holds cells in position (reduced levels are linked to tumor metastasis) § Beneficial to cancer cells = prevents them from escaping and multiplying → They serve as a biological glue for cells → Scant in epithelial tissue; abundant in connective tissue → Secreted by fibroblasts ○ Special cell type that makes these protein fibers SPECIALIZED CELL JUNCTIONS → CAMs provide some tissue cohesion as they "Velcro" adjacent cells together ○ More useful in signaling and communication → Cells are directly linked by one of three types of specialized cell junctions: → Desmosomes (adhering junctions) ○ Strongest cell to cell conjunction / connections ○ Most abundant in tissues that are subject to considerable stretching § Found in the skin, liver, uterus and heart ○ Act like "spot rivets" that anchor together two adjacent but non-touching cells Picture description: ○ Each cell has a cytoplasm thickening plaque that has intracellular keratin filaments attached to them from the INSIDE ○ In-between cells are intercellular filaments that connect together ○ Desmosomes is the unit of 2 cells' intercellular filaments joined → Tight Junctions ( impermeable junctions) ○ Adjacent cells firmly bind together at points of contact to seal off the passageway between the two cells ○ Found primarily in sheets of epithelial tissue such as those that cover the body and line internal cavities ○ Impermeable barrier ○ Cells touch ○ This gives the cell membrane full control of what can pass through into the cell Picture description: ○ Epithelial sheet lining the digestive tract separates the food and potent digestive juices within the inner cavity (lumen) from the blood vessels on the other side ○ There are strands of junctional proteins that hold the cells together - Think of it as the walls being sewed together Picture description: ○ A gap exist between adjacent cells, which are linked by small, connecting tunnels (formed by connexons) → Gap junctions ( communicating junctions) ○ Acts as a tunnel for 2 cells or a series of cells that are around each other ○ Connects cellular membranes but they do not touch ○ Allows for faster communication ○ Communicating junctions (permits small, water soluble particles to pass between the connected cells but precludes passage of large molecules) § Allows small ions, but not lipids, glucose, or anything big ○ Abundant in cardiac muscle and smooth muscle - allow movement of ions to transmit electrical activity -> synchronized contraction of a whole muscle mass)

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