Diagram showing the two forms of
cell signaling: chemical signaling and receptor-mediated signaling.
Many living organisms contain billions of cells that carry out diverse
functions. In order for the cells to cooperate, cells need to be able to
communicate with each other. Many of the genes that cells are capable of
synthesizing are thought to be involved in cellular signaling (a.k.a. signal
There are two methods of cell signaling: 1. cells secrete chemical signals
that can be transported to distant cells. 2. that will enable them to
communicate with other cells through physical contact.
Chemical signaling can be classified into three categories: local-chemical
mediator, hormone, and neurotransmitter. In the local-chemical mediator model,
the secreted chemical acts on the cells in the immediate environment. Hormones
are used for communication with distant target cells. For example, cells can
secret a chemical and rely on the blood system to deliver the signal to a
distant cell. Finally, neurotransmitters are secreted by neurons to stimulate an
adjoining cell. For example, a neuron might secrete acetylcholine to stimulate
the movement of a muscle cell.
Diagram showing the three different forms of chemical signaling: local chemical mediator,
neurotransmitter, and hormone.
Cells also depend on direct interactions between surface receptors to
communicate. Oftentimes, when the two cells bind together with their receptors
and ligands, the shape of the receptor is changed and can induce the
phosphorylation of an ADP molecule. This can then initiate a cascade of events.
Receptor-mediated signaling is also observed in the immune system. For
example, white blood cells (T-lymphocytes) will bind to foreign proteins on a
cell's surface when a cell has been infected. This binding-induced signaling
will initiate a immune response.
Much research have been focused on different modes of cellular signaling. A
better understanding of the different chemical signals and their
associated-pathways can provide insights to cures for cancer, AIDS, and many
other prominent diseases.