Cells and Their Organelles: 2) Junctions and Communication

 Junctions and Communication

Cells are packed very tightly next to each other inside living organisms. If you've ever seen an onion cell under a microscope, you'd see the plant cells all right next to each other. There are practically no gaps between cells. In the images below, each rectangular shape is a cell. The purple color is due to staining (adding color) so it's more visible. 

In order to pass information between cells, as well as things like ions and molecules, cells need a way of communication. This comes in the form of junctions. Junctions can be 'seams' or 'gaps' between cells that either increase or decrease communication and allow for the passage of molecules. 

Plasmodesmata - found only in plant cells. Has a small channel that directly connects the cytoplasm of neighboring plant cells via traversing the cell wall. Its goal is to move water, nutrients, and other molecules between cells. It increases communication because molecules, solutes, and water pass between cells through this type of junction. 

Gap Junction - found only in animal cells. Has a small channel that directly connects the cytoplasm of neighboring animal cells through the cell membrane. Its goal is to move ions, molecules, and water. It increases communication because molecules, solutes, and water pass between cells through this type of junction. 

Tight Junction - found only in animal cells. It forms a tight seal between adjacent cells by linking membrane proteins, creating a barrier. This prevents the leakage of molecules between cells. It decreases communication because it stops the passage of materials between cells. 

Desmosome - adheres cells together. Two adjacent cells are attached. A desmosome is made out of protein plaques in the cell membrane linked by filaments. It supports movement and mechanical stability. 

The following molecules are not junctions but are also used for communication or for the passage of molecules, similar to junctions. 

Membrane Proteins: There are two types, as follows. 

    - Peripheral Proteins: loosely bound to the surface of the membrane. Examples include receptors and markers. 

    - Integral Proteins: transmembrane proteins that penetrate the lipid bilayer, usually across whole membranes. Examples include transport proteins like channels and ion pumps (we'll get into that in an upcoming lesson). 

Membrane Carbohydrates (antigens): they give the cell the ability to distinguish one cell from another. Important in tissue and organ development. These are the basis for rejection of foreign cells by the immune system (this lesson comes up WAY later). 

Now for the joke! How do trees access the internet?

They log in!

(haha)

That's it! Next up: Types of Transport in Cells!