Last updated: April 27, 2022 Show
Summary In signal transduction, extracellular signals are converted into intracellular signals: A signaling molecule (ligand) reaches its target cell and binds to a specific receptor. This activates a signaling cascade involving intracellular enzymes and molecules (second messengers), which again leads to a specific reaction. Via signal amplification, the number of signaling molecules is increased at every step of the signal cascade. TerminologyOverviewReceptorsLigands of the intracellular receptors (Progesterone, Estrogen, Testosterone, vitamin D, Cortisol, Aldosterone, Thyroid hormones): PET Da CAT G protein-coupled receptorsG protein-coupled receptors (GPCRs) are the largest family of membrane receptors. The action of GPCRs depends on three elements: the receptor, the G protein, and the effector molecule. Gs proteins activate adenylyl cyclase, whereas Gi proteins inhibit adenylyl cyclase. Receptor tyrosine kinases (RTKs)Receptor tyrosine kinases are transmembrane receptors that are generally activated by ligand-induced dimerization and autophosphorylation of cytoplasmic tyrosine residues, which triggers activation of downstream signaling cascades. Ligands of the tyrosine kinase receptors (TYRosine kinase, INSULin, GROWth factors): “I'm TYRed of your INSULts, GROW up!” Non-receptor tyrosine kinasesLigands of the non-receptor tyrosine kinase (Prolactin, Interleukins/IFN, Growth hormone, G-CSF, Erythropoietin, Thrombopoietin): PIGGLET Receptor serine/threonine kinasesSince most ligands of ligand-gated ion channels are neurotransmitters, only a short overview is provided here. Second messengersSecond messengers are small molecules that mediate the intracellular response to an extracellular stimulus. SynthesisEffectscAMP activates ; protein kinase A (PKA). DegradationcAMP is degraded by phosphodiesterase to adenosine monophosphate (AMP). Examples of ligand hormonesSoluble guanylate cyclase is activated by nitric oxide. The second messengers cAMP and cGMP are degraded and inactivated to AMP and GMP by various phosphodiesterases (PDE). A decrease in cAMP or cGMP causes contractions in smooth muscles. PDE inhibitors are used in the treatment of pulmonary hypertension (PDE-4 inhibitor roflumilast) and erectile dysfunction (PDE-5 inhibitor sildenafil). Ligands of the guanylate cyclase (GMP, BNP, EDRF, ANP): GruMPy BEA Nitric oxide (NO) has a half-life of only a few seconds. It is not stored by the body but is synthesized as a result of activation. Nitrate drugs stimulate the formation and release of NO. Relaxation of smooth muscle cells in vessel walls leads to the dilation of coronary arteries, pulmonary arteries, and peripheral veins. Peripheral vasodilation leads to a decrease in cardiac preload. Gq proteins activate phospholipase C, which cleaves the second messengers IP3 and DAG from PIP2. These, in turn, activate PKC. Ligands of the phosphoinositol signaling pathway (TRH, Vasopressin, Angiotensin, GnRH, Oxytocin, Gastrin, Histamine): TRy VAn GOGH Ca2+ mediates the effect of other second messengers such as IP3 and DAG via PKC activation. It also functions as a second messenger by acting directly, i.e., without activating another signaling molecule. How are cAMP considered in the signal transduction pathway?Adenosine 3′,5′-cyclic monophosphate (cAMP) is a nucleotide that acts as a key second messenger in numerous signal transduction pathways. cAMP regulates various cellular functions, including cell growth and differentiation, gene transcription and protein expression.
What is receptors in signal transduction?Receptors are generally transmembrane proteins, which bind to signaling molecules outside the cell and subsequently transmit the signal through a sequence of molecular switches to internal signaling pathways.
Is cAMP a ligand that activates a signal transduction pathway?A ligand binds to a receptor, leading indirectly to activation of adenylyl cyclase, which converts ATP to cAMP. cAMP binds to protein kinase A and activates it, allowing PKA to phosphorylate downstream factors to produce a cellular response.
What forms a signal transduction pathway?Signal transduction pathway involves the binding of extracellular signaling molecules and ligands to receptors located on the cell surface or inside the cell that trigger events inside the cell, to invoke a response. The response can then alter the cell's metabolism, shape, and gene expression (Krauss, 2006).
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What type of receptor mediates the signal transduction pathway associated with camp?
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