18. Intercellular junctions

Question 1

The different Intercellular junctions? Integrins? Tight Junctions? GAP Junctions? Anchoring junction?

Answer 1

MEMBRANE JUCNTIONS: INTEGRINS

Intercellular junctions: points at which cells are held

• Integrins are transmembrane proteins- they bind to specific proteins in the extracellular matrix and to membrane proteins on adjacent cells
• Integrins help to organize cells into tissues
• Responsible for transmitting signals from the extracellular matrix to the cell interior
• If 2 cells are adjacent, but separated - they may be juncture (connected) by desmosomes
• Desmosomes:
• Dense accumulations of protein at the cytoplasmic surface of plasma membranes of both separate cells.
• They are infiltrated w/ protein fibres that extended into either cell.
• Purpose/ function of desmosomes = hold adjacent cells in place in areas subject to stretching (e.g. skin)

TIGHT JUNCTIONS:

• These junctions are formed by actual physical joining of the extracellular surfaces of two adjacent plasma membranes.
• Tight junctions are important in areas where more control over tissue processes is needed (epithelial cells in the intestine - involved in absorption)

ANCHORING JUNCTIONS:

o Can be divided into:

• Desmosomes junctions
• Hemidesmosomes junctions
• Adherens junctions
• These junctions use dense collections of proteins (keratin/des-min) to joint together cells.
• These intermediate filaments bind in slightly different ways depending on the type of anchoring junction.

GAP JUNCTIONS:

o Allows direct chemical communication b/w cells through diffusion without contact of ECM.
- These junctions effectively have 6 connexin proteins- forming a cylinder connecting the 2 cells.
o This pore is called a Connexon
- The polarity of the pore can be altered depending on the proteins that need to be transferred.