Signal transduction is the transmission of external and internal stimuli in the organism. Receptor proteins, second messengers, and enzymes are primarily involved in this signal transduction. Defects in signal transduction underlie most diseases, such as cancer and autoimmune diseases.
What is signal transduction?
By means of physiological signal transduction or signal transduction, body cells respond to external and internal stimuli. By means of physiological signal transduction or signal transduction, body cells respond to external and internal stimuli. In this process, a signal is transformed and penetrates into the interior of a cell, where it triggers the cellular effect through a signal chain. In this way, signals can be transmitted from one body compartment to another. Cells are thus able to communicate with each other. Signal transmission occurs either at one level or at multiple levels. When several levels connected in series are involved in the process, it is called a signaling cascade. Enzymes and secondary messengers are involved in signal transduction. Therefore, we often speak of an enzyme-mediated biochemical process in which biological information is transmitted via carriers. Signals from different sources are coordinated in the cytoplasm or nucleus. Together, the different signaling pathways of a cell type form what is known as the signaling network. Immune responses and muscle contractions, as well as visual and olfactory perceptions, all rely on signal transduction.
Function and task
Proteins are found on the cell membrane and inside a body cell. These proteins serve as receptors. Signaling molecules attach to receptor proteins on the surface. Thus, the receptors receive signals from outside or inside and transmit them to the inside of the cell for processing. The best-known signaling molecules include neurotransmitters and hormones, for example. There are many different receptors in the human body. Cystolic receptors, for example, are located in the viscous portion of the cytoplasm. This type of receptors mainly includes steroid receptors. To be distinguished from these receptors are the membrane receptors. They have an intracellular and an extracellular level. Thus, they are capable of signal molecule binding outside the cell. To allow the signal to penetrate inside, they change their spatial structure. The signal itself does not penetrate the cell. Instead, the signal information reaches the inside of the cell via biochemical processes of the proteins. These biochemical processes are controlled by hydrophilic substances such as neurotransmitters. Membrane-bound receptors are either ion channels, G protein-coupled receptors, or enzyme-coupled signaling pathways. Ion channels are transmembrane proteins. They are either activated or deactivated by a signal. The permeability of the membrane thus increases or decreases for certain ions. Ion channels are particularly relevant for nerve signals. G protein-coupled receptors stimulate a G protein to replace bound GDP with the chemical compound GTP. This causes the G protein to break down into α and βγ units, both of which transmit the signal. G protein-coupled receptors are involved in processes such as vision and olfaction. Enzyme-coupled 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 relation to these signaling pathways. Regardless of the signaling pathway, the transmission of internal and external signals to effector proteins inside the cell is the actual goal of signal transduction. This transduction occurs via targeted interactions between multiple proteins. Activation of signaling proteins and intracellular signaling proteins plays a major role in this process. Some signals are amplified by simultaneously activating multiple effector proteins. Second messengers are particularly relevant for the interconnection of signal transduction pathways and the integration of different signals. These are interfaces of different pathways that can trigger cell-specific responses. Signal transduction enables a unicellular organism to adapt to its environment, for example through sotff metabolism regulation or gene expression. In this way, the process enables the survival of the unicellular organism.In multicellular organisms, signal transduction enables the reception and processing of internal and external stimuli. Signal transduction is therefore also irreplaceable for their survival. Cell growth, cell division, and cell death, for example, are influenced by the processes described.
Diseases and disorders
When signaling pathways are disrupted, this disruption can result in various diseases. Cancers, diabetes, kidney disease, and autoimmune diseases have been shown to be related to defects in signal transduction. A signaling molecule usually binds to one of the described receptors on the surface of a cell and can trigger cell divisions in a complex response. In cancer, mutations in coding genes for signaling molecules, receptors, or enzymes result in increased or misdirected signaling pathway activity. This results in an increase in cell division stimulation. In this context, enzymes involved in transduction play a major role. They often exhibit increased activity in cancer. Pharmacology therefore wants to selectively inhibit these enzymes in the future and thus develop an anti-cancer drug. Even apart from anti-cancer agents, medical research is currently (as of 2015) intensively engaged in the development of cures based on processes of signal transduction. Even cholera, whooping cough, and widespread common ailments such as hypertension are associated with defects in signal transduction that are thought to be facilitated by certain external stimuli. The drugs available today for various diseases also already specifically interfere with signal transduction. In the future, this intervention is likely to become even more targeted and goal-directed.
