SIG - Cell Communication [LESSON]

Cell Communication

Cells communicate using chemical signals, which are proteins or other molecules secreted by one cell and released to a target cell. These molecules are also called ligands. Not all cells can “hear” a particular chemical message. Look at the image below – what does the cell have to have in order to “hear” and respond to a signal?

 

 

 

What does the cell use to be able to respond to a signal?

The cell has to have a receptor protein to fit the shape of the ligand.

 

Types of Signaling

There are many ways to classify types of cellular signaling. One convenient way to classify is by using distance between the source and target cell.

Long-distance signaling uses the release of hormones into the bloodstream or lymph to travel all around the body of the organism. An example of this would be the endocrine system in humans. For example, the pituitary releases growth hormone (GH), which promotes growth, particularly of the skeleton and cartilage. Like most hormones, GH affects many different types of cells throughout the body. However, cartilage cells provide one example of how GH functions: it binds to receptors on the surface of these cells and encourages them to divide

 The signaling cell emits ligand (red dots) into the bloodstream to travel to the target cell.

Direct-contact signaling is another type and involves the transmittance of a signal from one cell to its neighbor. This allows a group of cells to coordinate their response to a signal that only one of them may have received. In plants, there are plasmodesmata (gaps) between almost all cells, making the entire plant into one giant network.

 The signaling cell touches the target cell which binds ligand (red dots) to their receptors.

In another form of direct signaling, two cells may bind to one another because they carry complementary proteins on their surfaces. When the proteins bind to one another, this interaction changes the shape of one or both proteins, transmitting a signal. This kind of signaling is especially important in the immune system, where immune cells use cell-surface markers to recognize “self” cells (the body's own cells) and cells infected by pathogens.

A natural killer (NK) immune cell recognizes a healthy cell of the body by binding

 

Local signaling involves cells that are near one another but not directly touching. Ligands diffuse through the space between cells but do not have to travel long distances. A great example of local signaling is the nervous system, where signals have to traverse a cleft between neurons called the synapse. When the sending neuron fires, an electrical impulse moves rapidly through the cell, traveling down a long, fiber-like extension called an axon. When the impulse reaches the synapse, it triggers the release of ligands called neurotransmitters, which quickly cross the small gap between the nerve cells. When the neurotransmitters arrive at the receiving cell, they bind to receptors and cause a chemical change inside of the cell (often, opening ion channels and changing the electrical potential across the membrane). The neurotransmitters that are released into the chemical synapse are quickly degraded or taken back up by the sending cell. This "resets" the system so the synapse is prepared to respond quickly to the next signal.

The top neuron releases neurotransmitter into the space between itself and the next neuron. 

 

Try the Cell Communication Classification below by selecting the correct term.

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