As human beings, our bodies are constantly experiencing changes and variations due to fluctuations in our external and internal environment. There is therefore a constant need to adapt to these changes in order to keep cells alive and the efficiency of our entire body. A set of structures called G proteins play an essential role in helping the body adapt to the fluctuations evoked. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”?Get the original essay G proteins are a family of membrane proteins, monomeric or heterotrimeric, that are bound to the inner surface of the cell membrane. They can be described as a bridge connecting membrane receptor and cellular effector as they act as signal transducers that communicate signals of various hormones, neurotransmitters, chemokines and autocrine and paracrine factors[1] to the cell via secondary messengers , such as cyclic AMP or IP3. They indeed interact with several cellular proteins, including ion channels, their corresponding G protein-coupled receptors – also known as GCPRs –, interceptins and kinases. Heterotrimeric G proteins are made up of three different (-tri-) (hetero-) subunits as their name suggests: alpha (Ga), the largest which contains the site for converting GTP to GDP to allow the renewal of the G protein cycle, the beta (Gß) and gamma (G?) subunits, each with a different amino acid composition[2], and therefore a different structure. When GDP binds to the alpha subunit, this subunit remains bound to the beta and gamma subunits, forming an inactive turmeric protein[3]. When an agonist binds to GPCRs, it causes a conformational change that is transmitted to the G protein, activating the latter. one by replacing GDP (ADP equivalent) with GTP (ATP equivalent). The release of the GDP molecule causes the alpha subunit to dissociate from the beta-gamma dimeric complex and become “active”. It is activated to mediate signal transduction via various enzymes such as phospholipase C and adenylyl cyclase. The ß? The dimeric complex is not attached to the membrane and can migrate around the cell membrane, moving away from the subunit, while remaining on the cytoplasmic side of the latter due to its hydrophobic nature. This process only stops with the hydrolysis of GTP to GDP, causing the alpha subunit and the β subunit? dimer to reassemble and return to its trimeric configuration, which is “inactive”. This occurs once the ligand or signal molecule is removed from the GCPR[4]. As we know today, there are many different types of heterotrimeric G proteins, with approximately 20 known types of Ga units. Despite their differences, they all act as biomedical switches that influence ion channels or the rate of production second messengers. These are proteins that, through a series of events called a signaling cascade, control the concentrations of second messengers inside cells. These 20 types are divided into 4 families of G proteins: the Gi, GS, Gq and G12/13[5] families which constitute the majority of G proteins present in the mammalian cell. Each initiates a unique downstream signaling pathway because the combinations of the three subunits comprising the heterotrimer are different. In this essay, we will focus only on the first three categories, namely Gs, GI and Gq. Alfred G. Gilman and his colleagues used biochemical and genetic techniques to identify thefirst G protein after the discovery of a link between the hormone receptor and the enhancer by Martin Rodbell and colleagues[6]. The first G protein identified as Gs was found to activate and stimulate the production of adenylyl cyclase molecules. It catalyzes the conversion of ATP into cyclic AMP (cAMP), a second messenger. Then, cAMP binds to protein kinase A. Shortly after this discovery, the Gi protein was discovered and found to inhibit the actions of the Gs protein, thereby reducing the production of adenylyl cyclase. Inside the cell, cAMP binds to other proteins such as ion channels to change cellular activity. The Gq protein is slightly different from the other two in that it is involved in the inositol system rather than the camp system. As mentioned previously, cAMP binds to protein kinase A. Protein kinase A is a heterotetramer composed of two types of subunits: catalytic and regulatory whose activity depends on the concentration of cAMP. Indeed, when the concentration of cAMP is high, cAMP binds to the active sites of the protein kinase, causing a conformational change which allows protein kinase A to release free catalytic subunits capable of catalyzing the phosphorylation of threonine and serine residues on target proteins. On the other hand, when cAMP concentrations are low, the protein kinase is inactive because cAMP cannot bind to it and therefore remains bound to a regulatory subunit dimer, unable to release subunits free catalytics. This signaling sequence ultimately ends with the action of phosphodiesterase, an enzyme that converts cAMP to AMP. In human exercise, the essential character of the Gs protein is clearly illustrated. During the fed state, when glucose is abundant, skeletal muscles work to convert this molecule into large polysaccharide molecules to store energy when needed. During exercise the body craves ATP, therefore this glycogen is broken down into glucose which will then go through glycolysis to satisfy the muscle's need for ATP and will then give rise to muscle contraction. This is because during exercise, the sympathetic nervous system is activated and chemical signals like epinephrine secreted by the adrenal medulla increase in the body's bloodstream, thereby increasing metabolic levels. Increased levels of epinephrine in the system cause activation of β-adrenergic receptors, a specific type of adrenergic receptor located on the muscle membrane bound to Gs proteins. Upon activation of these receptors, the GTP-binding protein dissociates, resulting in the activation of adenylyl cyclase, which then leads to higher Camp concentrations. cAMP activates protein kinase A which then activates glycogen phosphorylase, an enzyme that facilitates the biological response of breaking down glycogen to glucose which releases the ATP necessary for muscle contraction. It then clearly shows that the activation of the Gs protein, more precisely the production of the second messenger, is important to allow humans to have the capacity to increase their mobility. Having seen that second messengers are key to human mobility, it is important that they are constantly regulated to ensure that muscles respond only when asked. Unlike Gs proteins, Gi proteins are here to inhibit the production of adenylyl cyclase, causing a drop in the intracellular concentration of cAMP. This effect is notable when acetylcholine binds to the muscarinic M2 AChR GCPR because once bound, the associated G protein is activated and the ß? The complex is separated from the subunit, allowing it to open or.