By physiological signal transduction or signal transmission, body cells respond to external and internal stimuli. A signal is transformed in this process and penetrates into the interior of a cell, where it causes the cellular effect through a signal chain. This allows signals to be transferred from one body compartment to another. Cells are thus capable of communicating with each other.
The signal transmission takes place either on one or more levels. If several levels connected in series are involved in the process, a signal cascade is mentioned. Enzymes and second messengers are involved in signal transduction. The talk is therefore often of an enzymatically mediated, biochemical process in which biological information on carriers are forwarded.
The signals of different sources are coordinated in the cytoplasm or nucleus. The different signal paths of a cell type together form the so-called signal network.
Both immune reactions and muscle contractions, as well as visual and olfactory perceptions rely on signal transduction.
At the cell membrane and inside a body cell are proteins. These proteins serve as receptors. Signal molecules close at the surface to receptor proteins. Thus, the receptors pick up signals from outside or inside and direct them into the cell for processing.
The best-known signal molecules include, for example, neurotransmitters and hormones. There are many different receptors in the human body. For example, cystolic receptors are in the viscous portion of the cytoplasm. Above all, the steroid receptors belong to this type of receptors. To distinguish from these receptors are the membrane-bound receptors. They have an intracellular and an extracellular level. Thus, they are capable of signal molecule binding outside the cell. In order to let the signal penetrate into the interior, they change their spatial structure.
The signal itself does not penetrate the cell. Instead, the signal information reaches the cell interior via biochemical processes of the proteins. These biochemical processes are controlled by hydrophilic substances such as neurotransmitters.
Membrane receptors are either ion channels, G protein-coupled receptors or enzyme-linked signaling pathways. Ion channels are transmembrane proteins. They are either activated or deactivated via a signal. The permeability of the membrane increases or decreases with it for certain ions. Especially for nerve signals, ion channels are relevant.
G protein-coupled receptors stimulate a G protein to replace bound GDP with the chemical compound GTP. Thus, the G protein breaks down into the units α and βγ, both of which relay the signal. The G protein-coupled receptors are involved in processes such as vision or smell.
Enzyme-linked signaling pathways consist of six subclasses. All of them correspond to transmembrane proteins. Processes such as kinase-mediated phosphorylation and phosphatase-mediated dephosphorylation play a role in these signaling pathways.
Regardless of the signaling pathway, the transmission of internal and external signals to effector proteins inside the cell is the ultimate goal of signal transduction. This forwarding takes place via targeted interactions between several proteins. Activation of signaling proteins and intracellular signaling proteins plays a major role in this process. Some signals are amplified by simultaneous activation of several effector proteins.
For the cross-linking of signal transduction pathways and the integration of different signals, especially second messengers are relevant. These are the interfaces of different pathways that can trigger cell-specific reactions.
The signal transduction enables a unicellular organism to adapt to its environment, for example, by Sotffwechselregulierungen or gene expression. Thus, the process only allows the survival of the unicellular. In multicellular organisms, signal transduction allows the absorption and processing of internal and external stimuli. Also for their survival, signal transduction is irreplaceable. Cell growth, cell division and cell death, for example, are influenced by the processes described.
When signaling pathways are disturbed, this disorder can result in various diseases. Cancer, diabetes, kidney disease and autoimmune diseases have been proven to be associated with signal transduction errors.
A signaling molecule usually binds to one of the receptors on the surface of a cell and can trigger cell divisions in a complex response. In cancer, mutations in coding genes for signaling substances, receptors or enzymes result in increased or misdirected signaling pathway activity. This results in an increase in cell division stimulation. In this context, especially the enzymes involved in the transduction play a major role. They often show increased activity in cancer. Pharmacology therefore wants to selectively inhibit these enzymes in the future and thus develop a cancer drug.
Apart from anti-cancer drugs, current medical research (as of 2015) is working intensively on the development of remedies based on signal transduction processes. Even cholera, whooping cough and widespread folk diseases such as high blood pressure are associated with errors in signal transduction, which are probably favored by certain external stimuli.
Even the currently available drugs for various diseases already targeted specifically in signal transduction. In the future, this intervention will presumably be made more targeted and more targeted.