Question

write down the function of adhering junction , gap junction and tight junctions​

Answer 1

Adherens junctions share the characteristic of anchoring cells through their cytoplasmic actin filaments. Similarly to desmosomes and hemidesmosomes, their transmembrane anchors are composed of cadherins in those that anchor to other cells and integrins in those that anchor to extracellular matrix. There is considerable morphologic diversity among adherens junctions. Those that tie cells to one another are seen as isolated streaks or spots, or as bands that completely encircle the cell. The band-type of adherens junctions is associated with bundles of actin filaments that also encircle the cell just below the plasma membrane. Spot-like adherens junctions help cells adhere to extracellular matrix both in vivo and in vitro where they are called focal adhesions. The cytoskeletal actin filaments that tie into adherens junctions are contractile proteins and in addition to providing an anchoring function, adherens junctions are thought to participate in folding and bending of epithelial cell sheets. Thinking of the bands of actin filaments as being similar to 'drawstrings' allows one to envision how contraction of the bands within a group of cells would distort the sheet into interesting patterns.

Communicating junctions, or gap junctions allow for 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. connexon complexes stretches across the cell membrane and when two adjacent cell connexons interact, they form a complete gap junction channel. Connexon pores vary in size, polarity and therefore can be specific depending on the connexin proteins that constitute each individual connexon. Whilst variation in gap junction channels do occur, their structure remains relatively standard, and this interaction ensures efficient communication without the escape of molecules or ions to the extracellular fluid.

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; however, movement of the solute is largely dependent upon size and charge. There is evidence to suggest that the structures in which solutes pass through are somewhat like pores.

Answer 2

Answer:

'Facilitate communication between adjoining cells by connecting the cytoplasm for rapid transfer of ions, small molecules, and some large molecules'.

Gap junctions can be defined as the specialized intercellular connection found between different animal cells. It directly connects the cytoplasm of two cells and allows the movement of different molecules, ions, and electrical impulses through a regulated gate between cells.

Explanation:

1. Adhering Junction:  Adherens junctions (AJs) are cell-cell adhesion complexes that are continuously assembled and disassembled, allowing cells within tissue to respond to forces, biochemical signals, and structural changes in their microenvironment.
2. Gap Junction:  Facilitate communication between adjoining cells by connecting the cytoplasm for rapid transfer of ions, small molecules, and some large molecules.
3. Tight Junction:  The purpose of tight junctions is to keep liquid from escaping between cells, allowing a layer of cells (for instance, those lining an organ) to act as an impermeable barrier.

For example, the tight junctions between the epithelial cells lining your bladder prevent urine from leaking out into the extracellular space.

Adherens junctions (or zonula adherens, intermediate junction, or "belt desmosome") are protein complexes that occur at cell-cell junctions, and cell-matrix junctions in epithelial and endothelial tissues, usually more basal than tight junctions.