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Swati Talwar

Cell Communication Study Guide

Cell communication or cell signaling is how cells receive, process, and transmit information with other cells and their environment.

Introduction

Our cells can detect what is happening around them and respond in real-time. They also take cues from the environment and its neighbors. Even during this second, your cells are taking and sending a million messages in the form of chemical signals. Cells thus communicate continuously. So how do cells communicate?

How do cells communicate with one another?

Simplified description of cell signaling Source

Cell communication happens through chemical signals produced by the cell. They are secreted from the cell, move to the extracellular space, and float to the neighboring cell.

The complete process involves the following steps:

  • The sending cell secretes the ligand.
  • The target cell has a receptor that binds the ligand. The ligand is bound to the receptor, and it triggers a signal cascades inside the cell and leads to the appropriate response.
  • The non-target cell does not contain any receptor for the ligand though it contains other kinds of receptors. The cell will neither perceive the ligand nor will it react to it.
  • Every cell does not hear a specific chemical message. To be a target cell, the neighbor cell should have the correct receptor.
  • When the signaling molecule binds to the receptor, it alters its activity and shape. This causes a change in the cell. The signaling molecule is the ligand. Thus, it is the term used for molecules that specifically bind to the other molecules.
  • The message that the ligand carries is relayed through chemical messengers inside the cell. It causes a change in the cell, such as altering the gene activity.

Cell-cell contact signaling

  • The gap junction in animals and the plasmodesmata in the plants are the tiny channels that connect neighboring cells directly.
  • These channels are filled with water and allow the small molecules called the intracellular mediators to diffuse between two cells.
  • Large molecules like macromolecules and proteins cannot fit in these channels without special assistance.
  • Signaling molecules transfer and transmit the current cell state to the neighbor, and this lets the cell group coordinate their response with a signal that only one of them could have received.
  • Plants have plasmodesmata between their cells that connect the whole plant like a network.
  • One cell targets its neighboring cell that connects through a gap junction
  • Thus cell to cell communication occurs from one to the other cell by passing through these gap junctions

How do cells communicate over long and short distances?

Cells processes to communicate Source

There are four main kinds of chemical signaling found in any multicellular organism, and the main difference between them is the distance that the signals travel to reach the target cell.

Paracrine signaling

Communication between cells situated close to one another occurs by releasing chemical messengers. This kind of signaling where the cells have to communicate over a short distance is called paracrine signaling.

Paracrine signals move by diffusion in the immediate extracellular environment when cells coordinate their activities locally. A synaptic signal across synapses between nerve cells is an example of paracrine signaling.

The nerve cells here will transmit the signal. The sending neuron will fire an electrical impulse that moves fast through the cell’s axon. The signal reaches the synapse and triggers the release of neurotransmitters. A synapse is a gap between 2 nerve cells. When the neurotransmitter reaches the receiving cell, they bond with the receptors and initiate an electrical impulse. The neurotransmitter is released in the chemical synapse and is degraded quickly to reset the system so that the synapse is ready to respond to the next signal.

Autocrine signaling

Here the cell will signal to itself by releasing a ligand that binds to the receptor present on its surface. This process plays a critical role in several processes. It is a crucial part of development where the cells reinforce the proper identity. This is important in cancer and plays a pivotal role in metastasis. The secretion of IL-1 by macrophages and the subsequent binding of IL-1 by receptors on macrophages is an example of autocrine signaling.

Endocrine signaling

When the cell has to pass a message over a long distance, they use the circulatory system’s distribution network for the message they send. Endocrine signaling comprises special chemicals called hormones released in the bloodstream from endocrine cells. These hormones target cells at a distance. Such signals from distant cells are called endocrine signals.

The thyroid, the pituitary, and the hypothalamus are the endocrine glands in humans. The glands release one or more hormones in low concentrations that play a role in psychology and development.

Conclusion:

  • Cells are in constant communication with each other.
  • Cell-cell communication is what makes you see and hear things as well as respond to stimuli.
  • There are various forms of cell signaling depending on the distance that the signal needs to cover.

FAQs:

1. What are the 4 types of cell communication?

The four kinds of cell communication are paracrine signaling, autocrine signaling, endocrine signaling, and signaling by direct contact.

2. How do cells communicate?

Cells send and receive signals and thus communicate with each other. The signals are in the form of chemical molecules called ligands which bind to receptors on the surface of the receiving cell.

3. What are cell signals?

Signaling cells secrete molecules called ligands that bind to target cells and initiate a chain of events within the target cell. These ligands are cell signals and help pass information from the sender to the receiver. Hormones and neurotransmitters are examples of cellular signals.

4. What is cell-cell contact?

It is the direct interaction between the surfaces of the cell. Fluid-filled channels called plasmodesmata, and gap junctions form these connections between the plasma membranes of neighboring cells. This connection between neighboring cells is called cell-to-cell contact.

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Sources:

  1. Signalling molecules https://openstax.org/books/biology-ap-courses/pages/9-1-signaling-molecules-and-cellular-receptors Accessed on 21 Dec, 2021
  2. Cell communication https://www.nature.com/scitable/topic/cell-communication-14122659/ Accessed on 21 Dec, 2021
  3. Cell communication (advanced) https://www.ck12.org/book/ck-12-biology-advanced-concepts/section/3.33/ Accessed on 21 Dec, 2021