cell membrane junctions Flashcards
(5 cards)
cells can move around freely but…
Even though some cells—like sperm cells, red blood cells, and phagocytes—can move freely, other types of cells, such as epithelial cells, are anchored in place and stick together to form tight communities.
how cell junctions are made
Glycoproteins in the glycocalyx act like cellular glue, helping cells stick together.
The wavy contours (shapes) of the plasma membranes of neighboring cells fit together like puzzle pieces—tongue-and-groove style—which helps them stay connected.
In addition to this, specialized cell junctions form between cells. These junctions can look and work differently depending on their function, and they help hold cells together firmly or allow communication between them.The glycocalyx helps with initial cell adhesion, but the actual cell junctions are formed by specific proteins in the plasma membrane—not just the glycocalyx alone.
“Basically, the glycocalyx helps the cell stick to and recognize other cells, the grooves provide extra support for alignment, and the specialized proteins are what actually form the junctions.”
Tight junctions
Tight junctions are impermeable junctions that encircle the cells and bind them together into leakproof sheets. In tight junctions, adjacent plasma membranes fuse together tightly like a zipper and prevent substances from passing through the extracellular space between cells. In the small intestine, for example, these junctions prevent digestive enzymes from seeping into the bloodstream.
Tight junctions are like waterproof junctions that seal cells tightly together, forming a leakproof barrier. They work by fusing the adjacent plasma membranes of neighboring cells like a zipper, which prevents substances from leaking between the cells.
Desmosomes
Desmosomes are specialized junctions that link adjacent cells together, but unlike tight junctions, they are not a continuous seal. Instead, desmosomes are scattered across the cells, acting like buttons or rivets that hold cells tightly together, giving tissues and organs strength and flexibility.
They are like button-like structures that hold the plasma membranes of adjacent cells together, but they allow the tissue to stretch and move without tearing.
Desmosomes are found on both sides of adjacent cells and are attached to each other through intermediate filaments (protein filaments) inside the cells, providing mechanical strength.
In short, desmosomes help ensure that tissues like skin and muscles can stretch and contract without tearing apart.
Gap junctions allow communication between cells. They are found in places like the heart and in embryonic cells.
Connexons are protein cylinders that form channels between adjacent cells.
These channels act like doors connecting two rooms (cells).
Through these water-filled channels, small molecules like nutrients and ions can pass directly from one cell to another.
Key points:
Gap junctions = cell communication.
Connexons = protein channels that connect cells.
They let molecules move directly between cells.
