cell adhesion molecules

Meaning: Cell adhesion molecules (CAMs) are membrane proteins that bind a cell to neighboring cells or to the extracellular matrix. Their intracellular ends usually link to the cytoskeleton, so they transmit force and signals as well as hold cells together. Cadherins bind the same cadherin on a neighbor (homophilic) and need Ca²⁺. Integrins are αβ heterodimers that bind matrix proteins such as fibronectin and collagen. Selectins bind carbohydrates and mediate white blood cells rolling along vessel walls. Immunoglobulin-superfamily CAMs, such as NCAM, do not need Ca²⁺.

On the MCAT: A passage removes Ca²⁺ or knocks out a CAM and asks what happens. Without cadherin function, cells dissociate and tissue integrity falls. You may also be asked to match protein to structure: cadherins in adherens junctions and desmosomes, integrins in hemidesmosomes and focal adhesions. Reduced cadherin is often linked to tumor cells detaching and spreading.

Common confusion: Cadherins and integrins get swapped. Cadherins join cell to cell and depend on Ca²⁺. Integrins join cell to matrix. Gap junctions are channels for small molecules, not adhesion molecules.