Signal Transduction Flashcards
What are the classes of cell signaling?
Endocrine- Into blood stream and effect a distal site.
Paracrine- Into ECM and affect nearby cells.
Autocrine- Into ECM and affect itself.
What are the classes of cell surface receptor, and what are examples?
Ligand-gated: Nichotinic ACh receptor.
Enzyme linked: RTK receptors like the insulin receptor.
GPCRs: Beta-adrenergic receptors.
Describe ligand gated ion channels.
Ligand binding causes a conformational change which then allows ions to pass, either depolaizing or hyperpolarizing the cell.
Fastest signal transduction speed.
Describe a general enzyme-linked receptor.
Growth factor binding leads to intrinsic enzymatic activity which causes a downstream signaling pathway.
Describe a receptor tyrosine kinase.
Ligand binding leads to autophosphorylation of itself, which intracellular proteins can then bind to and be substrates for phosphorylation as well.
Resulting activity may last for minutes to hours.
What is a cytokine, and how does its receptor differ from an enzyme-linked?
Cytokines are polypeptides that regulate growth, and examples are interleukins and interferons. Ligand binding causes a conformational change in the receptor, which THEN activates a protein kinase, either directly or indirectly (no intrinsic kinase activity).
What is the structure of a GPCR? What are the broad types?
7 transmembrane alpha helices exist, and intracellularly are associated with an intrinsic GTPase G protein.
Gs: alpha subunit stimulates adenylyl cyclase.
Gi: Inhibits adenylyl cyclase.
Gq: Activates phospholipase C.
Is activation of second messengers via GPCRs linked to the ligand type or receptor type?
Receptor. Same ligand can bind stimulatory or inhibitory GPCRs, leading to activation or inhibition of adenylyl cyclase.
What is the role of cAMP?
It binds to regulatory subunits of PKA, thus releasing the catalytic subunit. Catalytic subunit is then free to phosphorylate substrates on serine or threonine residues.
What eventually shuts of signaling via cyclic nucleotides?
Phosphodiesterases via breaking down the cNMP.
Describe the IP3/DAG system.
Glucagon or epi binding to stimulatory Gq GPCRs lead to activation of phospholipase C, which hydrolyzes PI to release IP3, which then mediates calcium release from the ER. Also DAG now binds and activates PKC.
What is the ultimate affect of insulin in terms of genes it promotes the expression of?
GLUT4 transporters in the membrane are increased leading to increased uptake, and glycogen and fat formation.
