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Cell Signalling
Cell to cell signalling is the transfer of information from one cell to another. It is also known as cell signalling or intercellular communication. This communication process happens through some chemicals known as chemical messengers. These chemical messengers are mostly protein molecules via which the body’s cells can interact with one another.
A chemical or physical signal is communicated through a cell and it happens as a succession of molecular processes. Most frequently it occurs as protein phosphorylation mediated by protein kinases, which eventually results in a cellular response. This process is termed as signal transduction. Signalling proteins have a significant role in signal transduction pathways, which regulate how cells react to different environmental cues. These proteins interact with one another and activate one another in a very specific manner.
Cell Signalling Molecules
- Hormones are the original endocrine messengers. A hormone is a chemical messenger that is produced by the endocrine glands and delivered by the blood to the intended organs or tissues which are the sites of action. Growth hormone and insulin are two examples.
- Growth hormones are proteins similar to cytokines that function as cell signalling agents. These substances interact with certain surface receptors on the target cell to promote cell growth, differentiation and/or maturation.
- Chemical messengers known as paracrine messengers go through the interstitial fluid from control cells to target cells. Through gap junctions, some of these messengers can enter the target cells next to them directly. Local hormones or juxtacrine messengers are other names for these compounds. Examples include histamine and prostaglandins.
- Chemical messengers known as autocrine messengers regulate the source cells that produce them. Therefore, another name for these messengers is intracellular chemical mediators. An example of this is leukotrienes.
- Neurotransmitters and neurohormones are examples of neurocrine or neural messengers. An endogenous signalling molecule known as a neurotransmitter is responsible for transmitting information from one nerve cell to another, as well as to muscles and other tissues. Acetylcholine and dopamine are two such examples.
- A molecule called a neurohormone is released by nerve cells into the blood and then delivered to the distant target cells. Oxytocin, antidiuretic hormone and hypothalamic releasing hormones are a few examples.
Explore:MCQs on Cell Signalling
Receptors
The most significant type of signalling proteins are receptors, which are typically found at the cell surface. They take in signals like neurotransmitters and hormones from other cells, activate signalling mechanisms within the cell, and ultimately cause cellular reactions.
- Most receptors are extracellular, which are essential transmembrane proteins. They cross the cell’s plasma membrane, with one receptor segment on the outside and the other on the inside.
- Cytoplasmic receptors and nuclear receptors are examples of intracellular receptors. They are soluble proteins that are restricted to specific regions of the cell. Non-polar hormones like the steroid hormones testosterone and progesterone are the most common ligands for nuclear receptors.
- There is also a class of integral transmembrane proteins known as G protein-coupled receptors that have seven transmembrane domains and are connected to a heterotrimeric G protein. In mammals, this is the biggest family of membrane receptors and proteins.
- Another such receptor is the tyrosine kinase receptor which is a transmembrane protein. It has an extracellular ligand-binding domain and an intracellular kinase domain. Examples include growth factor receptors like the insulin receptor.
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