As humans, our bodies continually face changes and variations due to fluctuations in both our external and internal environments. Therefore, there is a constant need to adapt to these changes to keep cells alive and our entire body efficient. A set of structures called G proteins play an essential role in helping the body adapt to the fluctuations mentioned. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an 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 the membrane receptor and cellular effector as they act as signal transducers that communicate signals from various hormones, neurotransmitters, chemokines, and autocrine and paracrine factors[1] to the cell via secondary messengers, such as an AMP cyclic or IP3. In fact, they interact with multiple cellular proteins, including ion channels, their corresponding G protein-coupled receptors - also known as GCPRs -, arrestins and kinases. Heterotrimeric G proteins are made up of three (-tri-) different (hetero-) subunits as the name suggests: the alpha (Ga), the largest which contains the site that allows the conversion of GTP into 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 the alpha subunit, it remains bound to the beta and gamma subunits, forming an inactive turmeric protein[3]. When an agonist binds GPCRs, it causes a conformational change that is transmitted to the G protein, activating the latter 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 dimer complex and become "active". It is activated to mediate signal transduction through various enzymes such as phospholipase C and adenylate cyclase. The ß? The dimer complex is not fixed to the membrane and can migrate around the cell membrane, 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 and ß subunits? dimer to reassemble and return to its trimeric configuration, which is 'inactive'. This happens 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 around 20 known types of Ga units. Despite their differences, they all act as biomedical switches that influence ion channels or the rate of production of second messengers. They are proteins that, through a series of events called a signaling cascade, control concentrations of second messengers within cells. These 20 types fall 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 that make up the heterotrimer are different. In this essay we will focus only on the first three categories, namely G, GI and Gq. Alfred G. Gilman and his collaborators used biochemical and genetic techniques to identify the first G protein after the discovery of a link between the hormone receptor and the amplifier by Martin Rodbell and his collaborators[6]. The first G protein to be identified as Gs was found to activate and stimulate theproduction of adenylate cyclase molecules. It catalyzes the conversion of ATP to cyclic AMP (cAMP), a second messenger. Then, cAMP binds to protein kinase A. Not long after this discovery, the Gi protein was discovered and found to inhibit the actions of the Gs protein, thus reducing the production of adenylate cyclase. Inside the cell, cAMP binds to other proteins such as ion channels to alter cellular activity. The Gq protein is slightly different from the other two in that it is involved in the inositol system rather than the field system. As mentioned above, 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 that allows protein kinase A to release free catalytic subunits that can catalyze the phosphorylation of threonine and serine residues on proteins. target. On the other hand, when cAMP concentrations are low, the protein kinase is inactive since cAMP cannot bind to it and therefore remains bound to a dimer of the regulatory subunit, unable to release free catalytic subunits. This signaling sequence is eventually interrupted by the action of phosphodiesterase, an enzyme that converts cAMP to AMP. In human exercise, the essentiality 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 for when it is needed. During exercise, the body craves ATP, so this glycogen is broken down into glucose which will then go through glycolysis to satisfy the muscle's need for ATP and thus give rise to muscle contraction. Indeed, during exercise, the sympathetic nervous system is activated and chemical signals such as adrenaline secreted by the adrenal medulla increase the body's blood circulation, thus increasing metabolic levels. Increased levels of adrenaline in the system cause activation of ß-adrenergic receptors, a specific type of adrenergic receptor on the muscle membrane linked to Gs proteins. Upon activation of these receptors, the GTP-binding protein dissociates, resulting in the activation of adenylate cyclase which then leads to higher Camp concentrations. cAMP activates protein kinase A which activates glycogen phosphorylase, an enzyme that facilitates the biological response of breaking down glycogen into glucose which releases ATP necessary for muscle contraction. It is therefore clarified that the activation of the Gs protein, more precisely the production of the second messenger, is important to allow humans to have the ability to increase their mobility. Since second messengers are fundamental to human mobility, it is important that they are constantly adjusted to ensure that muscles respond only when required. In opposition to Gs proteins, Gi proteins are here to inhibit the production of adenylate cyclase, causing a decrease in the intracellular concentration of cAMP. This effect is notable when acetylcholine binds to the muscarinic GCPR M2 AChR since once bound, the associated G protein is activated and the ß? The complex is separated from the subunit, making it free to open or interact with the heart's potassium channels. This is a mechanism used by the parasympathetic nervous system to slow the heart rate as it causes potassium ions to escape from the cells and therefore the cells become less excitable. We can say that Gq proteins are.