Forms of Intracellular Signaling

Introduction

  • 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:
  1. Contact dependant signaling
  2. Paracrine signaling
  3. Synaptic signaling
  4. 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.

Forms of Intracellular Signaling

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