Forms of Intracellular Signaling
- Cell signaling is part of any communication process that governs the basic activities of cells and coordinates cell actions.
- It is the ability of cells to perceive and correctly respond to their microenvironment that is the basis of development, tissue repair, immunity, and homeostasis.
- Communication between cells is common in nature.
- The cells of multicellular organisms use a variety of molecules as signals, such as peptides, proteins, amino acids, nucleotides, steroids, and lipids.
Forms of Intracellular Signaling
- Cell signaling can be classified as mechanical and biochemical based on the type of the signal.
- Mechanical signals are the forces exerted on the cell and produced by the cell.
- Biochemical signals are the biochemical molecules such as proteins, lipids, ions, and gases.
- These signals can be classified based on the distance between signaling and responder cells.
- Signaling between and amongst cells is divided into the following:
- Contact dependant signaling
- Paracrine signaling
- Synaptic signaling
- Autocrine signaling
1. Contact Dependant Signalling:
- Gap junctions in animals are connections between the plasma membranes of neighboring cells.
- These water-filled channels allow small signaling molecules, called intracellular mediators, to diffuse between the two cells.
- Small molecules, such as calcium ions (Ca2+), are able to move between cells, but large molecules, like proteins and DNA, cannot fit through the channels.
- The specificity of the channels ensures that the cells remain independent, but can quickly and easily transmit signals.
- The transfer of signaling molecules communicates the current state of the cell that is directly next to the target cell; this allows a group of cells to coordinate their response to a signal that only one of them may have received.
2. Paracrine Signalling:
- Signals that act locally between cells that are close together are called paracrine signals.
- Paracrine signals move by diffusion through the extracellular matrix.
- These types of signals usually elicit quick responses and last for a short duration.
- Paracrine ligand molecules are quickly degraded by enzymes or removed by neighboring cells.
- Paracrine signaling plays an important role in early development, coordinating the
activities of neighboring cells
- One example of paracrine signaling is the transfer of signals across synapses between nerve cells.
3. Synaptic Signalling:
- The cells of the nervous system provide rapid communication with distant cells.
- Their signal molecules, neurotransmitters, do not travel to the distant cells through the circulatory system like hormones.
- The long, fiber-like extensions of nerve cells release neurotransmitters from their tips very close to the target cells.
- The narrow gap between the two cells is called the chemical synapse.
4. Endocrine Signalling:
- Signals from distant cells are called endocrine signals; they originate from endocrine cells.
- In the human body, many endocrine cells are located in endocrine glands such as the thyroid gland, hypothalamus, and pituitary gland.
- These types of signals usually produce a slower response but have a long-lasting effect.
- The ligands released in endocrine signaling are called hormones, signaling molecules that are produced in one part of the body but affect other body regions some distance away.
- Hormones travel large distances between endocrine cells and their target cells via the bloodstream.