Cell Adhesion and Cell Junctions

Comprehensive vocabulary flashcards covering cell junctions, tissue organization, and cell adhesion molecules as described in the lecture notes.

Cytology

The study of cells.

Histology

The study of tissues.

Tissues

Groups of similar cells that work together to carry out a specific function, such as epithelial, muscle, or nervous tissue.

Epithelium

A tissue organisation where cells are tightly packed, forming mechanical and chemical barriers with distinct apical and basal polarity.

Mesenchyme

Connective tissue consisting of loosely packed cells surrounded by extracellular matrix (ECM) with little contact to other cells.

Epithelial-mesenchymal transition (EMT)

A process where epithelial cells become mesenchymal, playing an important role in embryonic development, inflammation, and cancer metastasis.

Mesenchymal-epithelial transition (MET)

A process where mesenchymal cells form epithelia.

Occluding junctions

Junctions such as tight junctions that seal cells together into sheets to form an impermeable barrier.

Communicating junctions

Junctions such as gap junctions that allow exchange of chemical or electrical information between cells.

Anchoring junctions

Junctions including adherens junctions, desmosomes, focal adhesions, and hemidesmosomes that attach cells and their cytoskeleton to other cells or the extracellular matrix.

Tight junctions

Junctions formed mainly by claudins and occludin that prevent the paracellular movement of fluids and molecules across the epithelium.

Zona occludens (ZO) proteins

Proteins that provide the intracellular link between tight junctions and the cytoskeleton.

Gap junctions

Hydrophilic channels that allow the exchange of ions and small molecules between cells with a membrane gap of $2-4\,nm$.

Connexon

A hemichannel made up of $6$ connexin molecules; two connexons in adjacent cells form a gap junction.

Homophilic interactions

Cell adhesion interactions that occur between similar molecules.

Heterophilic interactions

Cell adhesion interactions that involve different molecules.

Selectins

Transmembrane cell adhesion molecules (E- and P-types) on endothelial cells that recognize leukocytes during rolling adhesion.

Diapedesis

The step in leukocyte extravasation mediated by PECAMs.

Cadherins

Large transmembrane glycoproteins that mediate homophilic cell adhesion in the presence of $Ca^{2+}$ ions and link to the actin cytoskeleton.

Adherens junctions

Cell-cell contacts where cadherins are linked by adapter proteins called catenins to the actin cytoskeleton, often forming an adhesion belt.

Desmosomes

Cell-cell contacts providing great tensile strength where cadherin-like molecules (desmoglein and desmocollin) link to intermediate filaments via plakins.

Integrins

Heterodimers of $\alpha$ and $\beta$ subunits that act as the main cell surface receptors for binding to adhesive glycoproteins in the ECM.

RGD sequence

The common recognition sequence $\text{Arg-Gly-Asp}$ found in ECM molecules like fibronectin that is recognized by integrins.

Focal adhesions

Contact points for mesenchymal cells in connective tissue where integrins link the ECM (fibronectin) with the actin cytoskeleton via talin.

Hemidesmosomes

Contact points of epithelial cells and the basal lamina where $\alpha 6/\beta 4$ integrins bind to laminin and link to intermediate filaments (keratin).

Junctional epidermolysis bullosa

A skin blistering condition caused by defects in laminin-binding integrins ($\alpha 6/\beta 4$), laminin 5, or collagen VII.