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Cellular communication is an umbrella term used in biology and more in depth in biophysics and biochemistry to identify different types of communication methods between living cells. Some of the methods include cell signaling among others. This process allows millions of cells to communicate and work together to perform important bodily processes that are necessary to survival. Both multicellular and unicellular organisms heavily rely on cell-cell communication.
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Intercellular communication
Intercellular communication refers to the communication between cells. Membrane vesicle trafficking has an important role in intercellular communications in humans and animals, e.g., in synaptic transmission, hormone secretion via vesicular exocytosis. Inter-species and interkingdom signaling is the latest field of research for microbe-microbe and microbe-animal/plant interactions for variety of purposes at the host-pathogen interface.
Reception
Reception occurs when the target cell (any cell with a receptor protein specific to the signal molecule) detects a signal, usually in the form of a small, water-soluble molecule, via binding to receptor protein. Reception is the target cell's detection of a signal via binding of a signaling molecule, or ligand. Receptor proteins span the cell’s plasma membrane and provide specific sites for water-soluble signaling molecules to bind to. These trans-membrane receptors are able to transmit information from outside the cell to the inside because they change conformation when a specific ligand binds to it. By looking at three major types of receptors, (G protein coupled receptors, receptor tyrosine kinases, and ion channel receptors) scientists are able to see how trans-membrane receptors contribute to the complexity of cells and the work that these cells do. Cell surface receptors play an essential role in the biological systems of single- and multi-cellular organisms and malfunction or damage to these proteins is associated with cancer, heart disease, and asthma.
Transduction
When binding to the signaling molecule, the receptor protein changes in some way and starts the process of transduction. A specific cellular response is the result of the newly converted signal. Usually, transduction requires a series of changes in a sequence of different molecules (called a signal transduction pathway) but sometimes can occur in a single step. The molecules that compose these pathways are known as relay molecules. The multistep process of the transduction stage is often composed of the activation of proteins by addition or removal of phosphate groups or even the release of other small molecules or ions that can act as messengers. The amplifying of a signal is one of the benefits to this multiple step sequence. Other benefits include more opportunities for regulation than simpler systems do and the fine- tuning of the response, in both unicellular and multicellular organism.
Response
A specific cellular response is the result of the transduced signal in the final stage of cell signaling. This response can essentially be any cellular activity that is present in a body. It can spur the rearrangement of the cytoskeleton, or even as catalysis by an enzyme. These three steps of cell signaling all ensure that the right cells are behaving as told, at the right time, and in synchronization with other cells and their own functions within the organism. At the end, the end of a signal pathway leads to the regulation of a cellular activity. This response can take place in the nucleus or in the cytoplasm of the cell. A majority of signaling pathways control protein synthesis by turning certain genes on and off in the nucleus.
Local
Communicating through direct contact is one form of local signaling for eukaryotic cells. Plant and animal cells possess junctions that connect the cytoplasm of cells adjacent to one another. These connections allow for signaling substances that were dissolved in the cytosol to easily pass between the cells that are connected. Animal cells contain gap junctions and can communicate through these junctions in a process called cell-cell recognition. Plant cells are connected through plasmodesmata. Embryonic development and the immune response rely heavily on this type of local signaling. In other types of local signaling, the signaling cell secretes messenger molecules that only travel short distances. These local regulators influence cells in the vicinity and can stimulate nearby target cells to perform an action. A number of cells can receive messages and respond to another molecule within their vicinity at the same time. This process of local signaling within animal cells is known as paracrine signaling.
Long distance
Hormones are used by both plant and animal cells for long-distance signaling. In animal cells, specialized cells release these hormones and send them through the circulatory system to other parts of the body. They then reach target cells, which can recognize and respond to the hormones and produce a result. This is also known as endocrine signaling. Plant growth regulators, or plant hormones, move through cells or by diffusing through the air as a gas to reach their targets.
Cell signaling and impacts
There are three different types of basic cell communication: surface membrane to surface membrane, exterior, which is between receptors on the cell, and direct communication, which means signals pass inside the cell itself. The junctions of these cells are important because they are the means by which cells communicate with one another. Epithelial cells especially rely on these junctions because when one is injured, these junctions provide the means and communication to seal these injuries. These junctions are especially present in the organs of most species. However, it is also through cell signaling that tumors and cancer can also develop. Stem cells and tumor-causing cells, however, do not have gap junctions so they cannot be affected in the way that one would control a typical epithelial cell. Upstream cells signaling pathways control the proteins and genes that are expressed, which can both create a means for cancer to develop without stopping or a means for treatment for these diseases by targeting these specific upstream signaling pathways. Much of cell communication happens when ligands bind to the receptors of the cell membrane and control the actions of the cell through this binding. Genes can be suppressed, they can be over expressed, or they can be partially inhibited through cell signaling transduction pathways. Some research has found that when gap junction genes were transfected into tumor cells that did not have the gap junction genes, the tumor cells became stable and points to the ability of gap junction genes to inhibit tumors. This stability leads researchers to believe that gap junctions will be a part of cancer treatment in the future.
Communication in cancer
Cancer cells will often communicate via gap junctions, which are proteins known as connexins. These connexins have been shown to suppress cancer cells, but this suppression is not the only thing that connexins facilitates. Connexins can also promote tumor progression; therefore, this makes connexins only conditional tumor suppressors.[5] However, this relationship that connects cells makes the spreading of drugs through a system much more effective as small molecules can pass through gap junctions and spread the drug much more quickly and efficiently. The idea that increasing cell communication, or more specifically, connexins, to suppress tumors has been a long, ongoing debate that is supported by the fact that so many types of cancer, including liver cancer, lack the cell communication that characterizes normal cells.
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