“Cell signalling is the process in which cells communicate with other cells within their body or with the external environment.”
Cell signalling occurs by several distinct pathways. Multicellular organisms need cell signalling to regulate different functions. For eg., nerve cells in coordination with muscle cells help in body movement.
Cell signalling can be intercellular as well as intracellular. Intracellular signals are produced by the same cells that receive the signal. Intercellular signals travel throughout the body. This permits specific glands to produce signals that act on different tissues.
Also Read: Cells
Types of Cell Signalling Molecules
Cell signalling molecules are of the following types:
- Intracrine ligands: These are produced by the target cell and bind to the receptor within the cell.
- Autocrine ligands: They function internally and on other target cells. For eg., immune cells.
- Juxtacrine ligand: These target the adjacent cells.
- Paracrine ligands: These target the cells in the vicinity of the original cells. For eg., neurotransmitters
- Endocrine ligands: These produce hormones.
Stages of Cell Signalling
Cell signalling takes place in the following three stages:
- Binding of the signal molecule to the receptor.
- Signal transduction, where the chemical signals activate the enzymes.
- Finally, the response is observed
Cell Signalling Pathways
The cell signalling pathways are either mechanical or biochemical. The cell signalling is categorized based on the distance it must travel. For instance, hydrophobic ligands include steroids and vitamin D3. these can diffuse across the plasma membrane of target cells and bind to the intracellular cells.
On the contrary, hydrophilic ligands bind to the receptors on the surface of the cell and are amino acid derived. These allow the signals to pass through the aqueous environment of our body without any assistance.
Cell Signalling Function
Intracellular receptors are a common types of cell signalling receptor located within the cell in the cytoplasm. The intracellular receptors are of two types:
- Nuclear receptors
- Cytoplasmic receptors
Nuclear receptors are special classes of proteins with diverse DNA binding domains that form a complex with thyroid hormones that enter the nucleus and regulate the transcription of a gene.
Ligand Gated Ion Channels
These allow hydrophilic ions to pass the plasma membrane. When a neurotransmitter such as acetylcholine binds to it, ions cross the membrane and allow the neural firing to take place.
G-Protein Coupled Receptors
These receptors receive a large number of signals from diverse groups. The mechanism of action starts when a ligand binds to the receptor. This activates the G-protein that transmits an entire cascade of enzymes. It also activates the second messengers that carry out several functions such as sight, inflammation, growth and sensation.
A ligand binds to the receptor tyrosine kinase that results in the dimerization of the kinase domains. The tyrosine kinase domains of the dimer then phosphorylate that allows the intracellular proteins to bind the phosphorylated sites and activate.
Also Read: Hormones
The message carried by the cells is passed through a chain of chemical messengers within the cells. This results in changes in the cell such as alteration in the gene activity or the entire process. Thus, an intercellular signal gets converted into an intracellular signal that stimulates a response.
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