Download cell-junctions - WordPress.com

Dealing with Neighbors
How do you deal with your neighbors? Do you have a nice, open channel of communication? Are you strongly bonded together? Do you try to keep yourselves apart by blocking each other's
view?
Neighboring plant and animal cells must also interact in one way or another. Sometimes they have open channels of communication, and other times they simply hold each other tight. Awe,
how sweet! This lesson covers four kinds of cell junctions. One found in plants and three found in animal tissues.
Plasmodesmata
Plant cell walls contain something known as plasmodesmata (plural for plasmodesma), which are narrow, membrane-lined microscopic channels that span plant cell walls. The word comes
from the Greek for bond: desmos.
Think of these channels as simply tunnels or bridges between neighboring plant cells. What do tunnels and bridges do for us humans? They facilitate the flow of information and material
between two points as trucks transport goods and mail when traveling through them. Of course, plant cells don't have trucks and don't have mail. Instead, we know that plasmodesmata allow
for the passage of the following between plant cells:




Water
Nutrients
Signaling molecules
In some cases, some proteins and even RNA molecules, with the latter being a piece of genetic code.
Gap Junctions
The closest animal tissue equivalent to plasmodesmata are gap junctions. A gap junction, also called macula communicans and communicating junction, is an intercellular junction found in
animal tissues that allows for physiological components to pass from cell to cell. Gap junctions are cylinders made of membrane proteins that form a pore between two cells. Inasmuch, a gap
junction directly connects the cytoplasm of two cells. And so, just like plasmodesmata, these gap junctions are like tunnels that allow for ions, amino acids, sugar, and other small molecules to
pass from one cell to another.
Desmosomes & Tight Junctions
While plasmodesmata and gap junctions allow for communication and continuity between cells, there are animal tissue junctions that are used for cell-to-cell adhesion, as opposed to
communication. Have you ever seen rivets fastening two pieces of metal together, causing them to tightly adhere to one another? These rivets are like a desmosome, also called macula
adherens or anchoring junction, which are localized, spot-welds, which function to maintain adhesion between adjacent cells.
Another intercellular junction that holds cells close to one another is called the tight junction, or zonula occludens, which is a kind of intercellular junction between cells, where the outer
portions of the cell membranes fuse together in a continuous seal. They remind me of the press and seal sandwich bags, where the two side of the bag, like two cell membranes, can fuse
together when pressed tightly against one another, to the point that nothing will pass through the tight seal. And so, this is why tight junctions prevent virtually any and all fluid from leaking
across a layer of epithelial cells, like those of the skin. Unsurprisingly, such tight junctions are found in between certain skin cells to help make us as watertight as possible.
Memory Aid
And, as a quick memory aid to help remember all the different animal cell junction terms, just remember that macula 'communica'ns allows for 'communica'tion between cells thanks to gap
junctions. Macula 'adhere'ns allows for cells to 'adhere' to one another thanks to desmosome. And, zonula 'occluden's 'occlude's, or stops the ability of extracellular fluid from passing through it.
Lesson Summary
Okay, let's tighten up this lesson by summarizing everything. We went over four types of cell junctions. Plasmodesmata (plural for plasmodesma) are narrow, membrane-lined microscopic
channels that span plant cell walls. They are most similar to a gap junction, also called macula communicans and communicating junction, an intercellular junction found in animal tissues
that allows for physiological components to pass from cell to cell.
While these two cell junctions allow for communication between cells, two other cell junctions allow for adhesion between cells. They are desmosomes and tight junctions. A desmosome, also
called macula adherens or anchoring junction, is a localized, spot-welds, which function to maintain adhesion between adjacent cells. A tight junction, or zonula occludens, is a kind of
intercellular junction between cells where the outer portions of the cell membranes fuse together in a continuous seal.