Cells Use Cell-Adhesion Molecules to Form TissuesCells in a tissue are joined by cell-to-cell junctions that rely on cell-adhesion molecules (CAMs) in the plasma membranes of neighboring cells.These junctions maintain the structure and function of tissues and organs.DefinitionCell-adhesion molecules (CAMs)Cell-adhesion molecules (CAMs) are proteins that span the phospholipid bilayer of the membrane.How CAMs Are Built and BindSome parts of a CAM sit inside the membrane, while others stick out into the space between cells.Junctions form when CAMs on adjacent cells bind through their outer parts.Symmetrical junctions form when both cells use the same CAM type, grouping similar cells together.Asymmetrical junctions form when different CAMs interact, linking distinct cell types into more complex tissues.HintCAMs are highly specific to the cells they bind, which keeps tissues correctly organized.Why Cell Adhesion MattersAdhesion maintains tissue architecture.It gives tissues structural integrity and supports functional links between neighboring cells.Some junctions control what moves between cells.They block extracellular movement of substances, keeping tissue compartments separate.They also allow controlled transport of substances when needed.Adhesion has roles in immunity and disease.In the immune system, CAMs help distinguish the body's own cells from foreign cells.In cancer, loss of adhesion can cause metastasis, as cells detach from the primary tumor and form secondary tumors elsewhere.ExampleIn the heart, gap junctions let electrical signals pass quickly between cardiac cells.This makes the heart contract as one coordinated unit.A Common Point of ConfusionCommon MistakeStudents often confuse cell adhesion with the extracellular matrix (ECM).CAMs directly link cells to each other, while the ECM provides a scaffold for cells to attach to.Active recallWhat are cell-adhesion molecules and where are they found?How does a symmetrical junction differ from an asymmetrical junction?How does cell adhesion help the immune system?Why can loss of cell adhesion lead to metastasis?How do CAMs differ from the extracellular matrix?
