Cell Signaling (Cell Communication)
Definition: Cell signaling is the ability of a cell to
receive, process, and transmit signals with its environment and with itself.
It is the basic property of all cells and is
essential for survival, growth and development of an organism.
Cells primarily communicates through chemical
signals or called ligands (signaling molecules).
Ligands are secreted by the sending cells and
the target cell has a receptor specific for this ligand. Binding of ligand to
the receptor causes some conformational changes that further activate some
other proteins inside the cell and finally causing a cellular response.
4 types of Cell signaling
Based on distance travelled by the ligands or
signaling molecule
1. Autocrine Signaling (self-communication): Cells respond to the
signal produced by themselves.
Eg: T cell proliferation and differentiation by cytokines secreted
by T cells itself
Secretion of IL1 by macrophages activates
macrophages itself.
2. Paracrine (para: nearby) (short distance signaling):
Signaling molecules produced by the sender cell affects neighboring target
cells
Eg: Synaptic signaling (conduction of an electrical
signal from one nerve cell to another at a synapse using neurotransmitter as
signaling molecules. Neurotransmitter released from the presynaptic cell binds to the receptor on the post synaptic cell causing cellular responses like opening of ion channel, change in membrane potential across the membrane etc.)
3. Endocrine Signaling (Long distance signaling): Signaling
molecules (hormones) are secreted by endocrine cells carried through the blood
stream to distant target cells
Eg: Signaling of hormones; Estrogen hormones
produced by ovary stimulates development and maintenance of female reproductive
system and associated secondary sex characteristics.
4. Direct cell to cell signaling: through gap junctions in animals and plasmodesmata in plants. Communication junctions allows ions and small molecules to pass through to the next cell ensuring direct intercellular communication. Direct cell to cell signaling is crucial in early embryonic development and maintenance of tissues.
