The earliest published scientific paper recorded in the MEDLINE database as containing the specific term "signal transduction" within its text was published in 1972. These figures were extracted through an analysis of the papers contained within the MEDLINE database. Occurrence of the term “signal transduction” The total number of papers published in each year since 1977 containing the specific phrase “signal transduction” in either their title or abstract section, are plotted. Many disease processes such as diabetes, heart disease, autoimmunity and cancer arise from defects in signal transduction pathways, further highlighting the critical importance of signal transduction to biology as well as medicine. Thus, sensing of both the external and internal environment at the cellular level, relies on signal transduction. As may be expected, the more complex the organism, the more complex the repertoire of signal transduction processes the organism must possess. In multicellular organisms, a multitude of different signal transduction processes are required for coordinating the behavior of individual cells to support the function of the organism as a whole. In bacteria and other single-cell organisms, the variety of signal transduction processes of which the cell is capable influences how many ways it can react and respond to its environment. In many signal transduction processes, the number of proteins and other molecules participating in these events increases as the process eminates from the initial stimulus, resulting in a " signal cascade" and often results in a relatively small stimulus eliciting a large response. Such processes are usually rapid, lasting on the order of milliseconds in the case of ion flux, to minutes for the activation of protein and lipid mediated kinase cascades. In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes and linked through second messengers resulting in what is thought of as a "second messenger pathway". 6.1.5 Ligand-gated ion channel receptors.Proliferation of damaged or malfunctioning cells is often a key factor in the generation of disorders such as cancer, infectious diseases, inflammation, arteriosclerosis, arthritis, and neurodegenerative diseases. In a healthy organism, the processes of cellular growth and differentiation are tightly controlled, but in the pathological state, are uncoupled in such a way as to result in further damage-causing signals, or the growth of the malfunctioning cells. In the last few years signal transduction therapy has become one of the most important areas of modern drug research. Activation of different signaling pathways leads to diverse physiological responses, such as cell proliferation, death, differentiation, and metabolism. One of the most important functions of cell signaling is to control and maintain normal physiological balance within the body. Activated receptors stimulate second messenger production, which in turn activate other enzymes and so the cascade continues. These include cAMP, cGMP, nitric oxide, lipids and Ca 2+ ions. Several small molecules within the cell act as intracellular messengers (also known as second messengers). Adding or removing phosphates is a fundamental mechanism for altering the shape, and therefore the behavior, of a protein. Signal transduction involves altering the behavior of proteins in the cascade, in effect turning them on or off like a switch. Signal transduction pathways amplify the incoming signal by a signaling cascade using a network of enzymes that act on one another in specific ways to ultimately generate a precise and appropriate physiological response by the cell. The intracellular component of signal transduction is highly receptor specific, thereby maintaining the specificity of the incoming signal inside the cell. Receptors that are found intracellularly and upon ligand binding directly alter gene transcription ( Nuclear Receptors).Receptors that are coupled, inside the cell, to G proteins ( 7-TM Receptors).Receptors that penetrate the plasma membrane and have intrinsic enzymatic activity or are enzyme associated ( Enzyme-linked Receptors).Signal transducing receptors are of four general classes: Receptors that initiate biochemical changes can do so either directly via intrinsic enzymatic activities within the receptor or by activating intracellular messenger molecules. Transmission is continued either by a series of biochemical changes within the cell or by modification of the cell membrane potential by the movement of ions in or out of the cell.
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