Cell junctions are multiprotein complexes that provide contact between adjacent animal cells and help hold tissues together. The main types are anchoring junctions, which attach cells to surrounding matrix and each other; gap junctions, which allow direct communication between cells; and tight junctions, which form barriers between epithelial layers. Cell junction molecules like selectins, cadherins, integrins, and the immunoglobulin superfamily mediate cell-cell adhesion through calcium-dependent and calcium-independent binding of domains on neighboring cell surfaces. Cell junctions are essential for tissue structure, cell signaling, and barrier functions in the body.

1. CELL JUNCTION
MADE BY:- AANSHI SRIVASTAVA

2. WHAT IS CELL JUNCTION
Cell junction (intercellular bridges) are
a class of cellular structures consisting
of multiprotein complexes that provide
contact or adhesion between
neighboring cells or between a cell and
the extracellular matrix in the animals.

3. Cell junctions are especially abundant in the
epithelial tissues. Combined with cell adhesion
molecules, and extracellular matrix, cell junctions
help hold the animal cells together.
Cell Junctions are also especially important in
enabling communication between neighboring
cells via specialized protein complexes called
communicating junctions. And, are also important
in reducing stress placed upon cells.

4. TYPES OF CELL JUNCTION

5. ANCHORING JUNCTION
• Cells within tissues and organs must be anchored to one another
and attached to components of the extracellular matrix.
• Anchoring junction not only hold cells together but provide
tissues with structural cohesion. These junctions are most
abundant in tissues that are subject to constant mechanical stress
such as skin, and heart.

6. GAP JUNCTION
• Gap junction (communicating junction) allow for the direct chemical
communication between adjacent cellular cytoplasm through diffusion
without contact with the extracellular fluid. This is possible due to
six connexin proteins interacting to form a cylinder with a pore in the centre
called a connexon.
• Gap junctions play vital roles in the human body, including their role in the
uniform contractile of the heart muscle. They are relevant in signal transfers
in the brain, and their absence shows a decreased cell density in the brain.

7. TIGHT JUNCTION
Found in vertebrate epithelia, tight junctions act as barriers
that regulate the movement of water and solutes between
epithelial layers. Tight junctions are classified as
a paracellular barrier which is defined as not having
directional discrimination. There is evidence to suggest
that the structures in which solutes pass through are
somewhat like pores.

8. TRICELLULAR JUNCTIONS
•Tricellular junctions seal epithelia at the corners of
three cells. Due to the geometry of three-cell
vertices, the sealing of the cells at these sites
requires a specific junctional organization, different
from those in bicellular junctions. In vertebrates,
components tricellular junctions are tricellulin and
lipolysis-stimulated lipoprotein receptors.

9. CELL JUNCTION MOLECULES

10. SELECTINS are cell adhesion molecules that play an important role in the initiation of inflammatory
processes. The functional capacity of selectin is limited to leukocyte collaborations with vascular
endothelium.
CADHERINS are calcium-dependent adhesion molecules. Cadherins are extremely important in the
process of morphogenesis – fetal development. Together with an alpha-beta catenin complex, the cadherin
can bind to the microfilaments of the cytoskeleton of the cell. This allows for homophilic cell–cell adhesion.
INTEGRINS act as adhesion receptors, transporting signals across the plasma membrane in multiple
directions. These molecules are an invaluable part of cellular communication, as a single ligand can be
used for many integrins.
IMMUNOGLOBULIN SUPERFAMILY are a group of calcium independent proteins capable of homophilic
and heterophilic adhesion. Homophilic adhesion involves the immunoglobulin-like domains on the cell
surface binding to the immunoglobulin-like domains on an opposing cell’s surface while heterophilic
adhesion refers to the binding of the immunoglobulin-like domains to integrins and carbohydrates instead
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