Signal transduction in the nervous system (SAQ)

Ionotropic receptors are ligand-gated ion channels with the fastest response time and are the rarest kind. Metabotropic receptors, on the other hand, are 7TM spanning G-protein coupled receptors with a second faster response time and are the most common.

G-proteins are molecular switches that carry information from receptor enzymes to effector enzymes. They are active when bound to GTP (guanine nucleotide triphosphate) and inactive when bound to GDP (guanine nucleotide diphosphate). The Gα complex is released when GTP is bound, regulating the effector enzyme.

When a hormone lands on the receptor, a G-protein with GDP bound associates with the receptor. GTP/GDP exchange occurs on the G-protein, leading to the dissociation of the G-protein into GTP-bound Gα subunit and bγ subunit. The Gα subunit then binds to the effector enzyme to activate it, leading to the production of a second messenger.

<p>Protein kinases are used as target proteins for neuronal signaling due to the balance of phosphorylation and dephosphorylation, which controls the signals for neuronal response. This balance is crucial in modulating the activity and function of proteins involved in neuronal signaling.</p> Signup and view all the answers

<p>Adenylyl cyclase converts ATP to cyclic AMP and can be both stimulated and inhibited depending on the Gα subunit that binds to it. cAMP activates protein kinase A which then goes on to phosphorylate potassium channels.</p> Signup and view all the answers

<p>Phospholipase E converts membrane phospholipid (PIP2) into diacylglycerol (DAG) and inositol-1,4,5-triphosphate (IP₃). DAG activates protein kinase C whereas IP₃ binds to receptors on smooth ER and other membrane-enclosed organelles, causing them to expel Ca2+ and can go on to stimulate other enzymes.</p> Signup and view all the answers

<p>nNOS is activated by CA2+ that enters when glutamate activates NMDA on g-protein. nNOS then catalyzes the reaction between arginine and oxygen to produce nitric oxide, which acts as a gaseous secondary messenger and diffuses to neighboring cells to activate guanylyl cyclase.</p> Signup and view all the answers

<p>RTK forms a dimer when the signaling molecule binds to it and activates tyrosine kinase, leading to receptor phosphorylation. This phosphorylation activates other proteins, continuing the signaling cascade. For example, RAS, a monomeric G-protein, is activated once the RTKs are phosphorylated.</p> Signup and view all the answers

<p>Nuclear receptor signaling modulates pathways in cell surface signaling. Membrane-permeable hormones bind to receptors in the nucleus, forming heterodimers that bind to specific DNA sites and regulate gene expression. For example, retinoic acid binds to RARS/RXRS receptor, forming a heterodimer RAR, which then binds to RARES DNA site.</p> Signup and view all the answers

<p>cAMP activates protein kinase A, which then goes on to phosphorylate potassium channels. It is produced by the conversion of ATP to cyclic AMP by adenylyl cyclase.</p> Signup and view all the answers

<p>DAG activates protein kinase C, whereas IP₃ binds to receptors on smooth ER and other membrane-enclosed organelles, causing them to expel Ca2+ and can go on to stimulate other enzymes.</p> Signup and view all the answers

<p>Guanylyl cyclase is activated by nitric oxide, which diffuses to neighboring cells to activate guanylyl cyclase, turning GTP into cGMP. cGMP then binds to protein kinase G, leading to downstream effects.</p> Signup and view all the answers

<p>Ionotropic receptors are ligand-gated ion channels, which provide the fastest response but are the rarest kind. An example is the nicotinic acetylcholine receptor. Metabotropic receptors are 7-transmembrane spanning G-protein-coupled receptors, which are the most common and have a second-fastest response. An example is the muscarinic acetylcholine receptor. Tyrosine-kinase linked receptors have a catalytic domain, are slower, and less common. An example is the insulin receptor.</p> Signup and view all the answers

<p>G-proteins are molecular switches that carry information from receptor enzymes to effector enzymes. They bind to guanine nucleotides (GTP) and are active when bound to GTP but inactive when bound to GDP. The Gα subunit complex is released when GTP is bound, which regulates the effector enzyme. G-proteins are involved in G-protein coupled receptors (GPCRs) and are heterotrimeric, consisting of three subunits.</p> Signup and view all the answers

<p>When a hormone binds to the receptor, the G-protein with GDP bound associates with the receptor. GTP/GDP exchange occurs on the G-protein, leading to the dissociation of the G-protein into GTP-bound Gα subunit and βγ subunit. The Gα subunit then binds to the effector enzyme to activate it, leading to the production of second messengers.</p> Signup and view all the answers

<p>Protein kinases are used as target proteins for neuronal signaling due to their role in controlling the signals for neuronal response. The balance of phosphorylation and dephosphorylation controls the signals for neuronal response, making protein kinases crucial in modulating neuronal activity.</p> Signup and view all the answers

<p>Protein kinase A is activated by cAMP, which is produced by adenylyl cyclase. Once activated, protein kinase A goes on to phosphorylate potassium channels, thereby regulating neuronal signaling.</p> Signup and view all the answers

<p>Nitric oxide is a gaseous secondary messenger that diffuses to neighboring cells to activate guanylyl cyclase, which converts GTP into cGMP. cGMP then binds to protein kinase G, leading to downstream effects in the target cells.</p> Signup and view all the answers

<p>Tyrosine kinase is activated when the receptor tyrosine kinase (RTK) forms a dimer and becomes phosphorylated. This phosphorylation activates other proteins, such as RAS, to initiate the signaling cascade in the cell.</p> Signup and view all the answers

<p>DAG activates protein kinase C, while IP₃ binds to receptors on smooth endoplasmic reticulum (ER) and other membrane-enclosed organelles, causing them to expel Ca2+, thereby stimulating other enzymes.</p> Signup and view all the answers

<p>Nuclear receptors bind to membrane-permeable hormones, forming heterodimers that bind to specific DNA sites. This leads to the regulation of gene expression. An example hormone involved in this pathway is retinoic acid, which binds to RARS/RXRS receptor and forms heterodimers to regulate gene expression.</p> Signup and view all the answers

<p>Phospholipase E is activated by G-protein signaling and converts a membrane phospholipid (PIP2) into diacylglycerol (DAG) and inositol-1,4,5-triphosphate (IP₃). DAG activates protein kinase C, while IP₃ binds to receptors on smooth ER and other membrane-enclosed organelles, causing them to expel Ca2+ and stimulate other enzymes.</p> Signup and view all the answers

<p>GTP is hydrolyzed to GDP, causing the Gα subunit to dissociate from the complex. This allows the G-protein complex to rejoin and become active again in the signaling cascade.</p> Signup and view all the answers

<p>Nitric oxide synthase (nNOS) is activated by Ca2+ that enters when glutamate activates NMDA on G-protein. nNOS then catalyzes the reaction between arginine and oxygen to produce nitric oxide (NO), which acts as a gaseous secondary messenger. NO diffuses to neighboring cells to activate guanylyl cyclase, initiating downstream effects in neuronal signaling.</p> Signup and view all the answers