Cell Signalling

Process during which cells communicate with other cells within their body or with an external environment, known as cell signalling. This process takes place by different distinct pathways. For regulation of various functions in multicellular organisms, we need cell signalling processes to occur. Example: When nerve cells work with muscle cells to help in body movement. Depending on the function, cell signalling can be both intercellular and intracellular. Intracellular signalling processes are produced by the same cells that receive signals whereas, in intercellular signalling processes, signals travel throughout the body. This signalling gives permission to specific glands to produce signals so that they can act on different tissues. 

Types of Cell Signalling:

Cell signalling is of various types. Some of the major types of cell signalling are discussed below:

A. Intracrine Ligands: Under this signalling process, signals are produced by the target cell and bind to the receptor within the cell. 

B. Autocrine Ligands: This signalling process does its function internally and on other target cells. For eg., immune cells.

C. Juxtacrine Ligand: In this type of signalling, they target the adjacent cells.

D. Paracrine Ligands: These ligands target the cells in the vicinity of the original cells. For eg., neurotransmitters.

E. Endocrine Ligands: Their main function is the production of different hormones. 

Stages of Cell Signalling:

There are several stages for cell signalling, but among them, three steps are considered important steps they are discussed below:

A. Binding of the signal molecule to the receptor:

Here, transduction of signals takes place. In this step, chemical signals activate the different enzymes. Due to this activation process response is observed. 

B. Cell Signalling Pathways:

This process occurs either in biochemical or mechanical pathways. Depending upon the distance travelled during cell signalling, we can categorise them into different types. 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 other hand, the surface of cell hydrophilic ligands bind to the receptor and they are mainly amino acid derivatives. This process allows the signal to pass through the aqueous environment of our body without help. 

Cell Signalling Function:

There are several important functions of the cell signalling:

A. Intracellular Receptors: 

One of the common types of receptor which is used in cell signalling is intracellular receptors. Further, these intracellular receptors are of two types:

1. Nuclear Receptors: Special class of proteins with different binding domains, which combine to form a complex with thyroid hormones, they are known as nuclear receptors. They enter the nucleus and regulate the transcription process of genes. 

2. Cytoplasmic Receptors: Internal receptors are mainly known as cytoplasmic receptors as they are present in the cytoplasm of the cell and they respond to hydrophobic ligands. Due to this, they are capable of travelling across the plasma membrane. 

B. Ligand Gated Ion Channels:

Through this channel movement of hydrophilic ions are allowed across the plasma membrane. Example: Neurotransmitters like acetylcholine bind to it, due to which ions cross the membrane and allow the neural firing to take place.

C. G-Protein Coupled Receptors:

All these receptors receive a large number of signals from various groups and this process starts when a ligand binds to a receptor. During this process, activation of the G-protein occurs due to which it transmits an entire cascade of enzymes. This receptor also activates the second messengers and these secondary messengers carry out several functions like sight, inflammation, growth and sensation.

D.Tyrosine Kinase:

When a ligand binds to the receptor tyrosine kinase, it leads to the dimerization of the kinase domains. Phosphorylation of tyrosine kinase domains of the dimer occurs to allow the intracellular proteins to bind the phosphorylated sites and activate.

With the help of different chemical messengers of the cells, the message carried out. This process leads to changes in the cells various processes: such as alteration in the gene activity or the entire process. Due to which, an intercellular signal gets converted into an intracellular signal that initiates a response.