BCOR 103 1st Edition Exam 3 Study Guide Lectures 15 20 Lecture 15 March 17 Cell Signaling in Nature detect nutrients detect energy light sources monitor environment cell cell communication coordinate cellular events Cellular Responses to Signals movement embryogenesis programmed cell death metabolism cell differentiation Overview of Eukaryotic Cell Signaling Cell signaling converting environmental input signals to output cellular responses Input signals light sound smell small molecules nutrients cell cell interactions Output cellular responses cell division differentiation development cell structural changes motility metabolism survival cell death Signal transduction transmitting input signal into cell to induce complex cellular responses through changes in gene expression or protein function Methods for Studying Signaling Pathways methods that examine cellular processes in response to specific signals or signaling pathways 1 Measure levels of protein expression immunoblot analysis Western Blot using antibodies to detect proteins 2 Examine protein protein interactions co immunoprecipitation GST pull downs two hybrid analysis 3 Enzymatic Assays establish enzyme activity 4 Microscopy visualize protein localization cell structure and DNA content Protein Kinase Mechanisms Protein Kinase and phosphatases modify functions of enzymes in response to signals Kinase puts phosphate groups on serine threonine or tyrosine amino acids phosphorylates them Phosphatases take the phosphate groups off Genetic Methods for Studying Signaling Pathways mutations activate or block pathways independent of signal used to determine relationships between signaling compounds Types of Cell Signaling Direct Cell to Cell Signaling Signaling by Secreted Molecules A Endocrine Signaling B Paracrine Signaling C Autocrine Signaling Overcoming Intracellular Obstacles to Proper Signaling Major obstacles o Passing signals through membranes and cytoplasm o Relative size of signaling molecule compared to the cell o Coordination of events right time right place Overcoming obstacles in signaling o Proper localization of signaling factors into membranes o Protein protein interactions multi protein complexes o Turn signals ON OFF by Molecular switches Phosphorylation Proteolysis o Signaling networks Simplified Classification of Signaling Components Signaling Molecules receptors transmitters ultimate target Gene Expression OR Protein Function Signaling Molecules the signal initiators Signals bind cell surface receptors expressed on plasma membranes of target cells or diffuse through plasma membrane to bind intracellular receptors Binding induces conformational and or enzymatic changes in receptors to initiate intracellular signaling Vary in structure o Gases peptides lipids etc o Structure determines type of signaling Vary in function o Varying distances modes of action Endocrine signals o Hormones secreted by endocrine cells o Carried through bloodstream o Act on target cells at distant body sites Endocrine signaling molecules o Hydrophobic steroid hormones o Related hydrophobic signaling molecules Target cells have receptors for binding specific hormones o pull appropriate hormones from extracellular fluid Sex hormones o Made by gonads o Required for development and maintenance of reproductive system Glucocorticoids cortisol o Stimulates production of glucose Mineralocorticoids aldosterone o Regulate salt and water balance in kidneys all synthesized from cholesterol Thyroid hormone o Role in development o Regulates metabolism Vitamin D o Regulates Ca functions Retinoic Acid o Synthesized from Vitamin A o Role in vertebrate development Hormone Receptors act as Transcription Factors Common Domains of steroid receptor superfamily hormone binding DNA binding transcriptional regulation nuclear targeting Steroid Hormone Binding activates Receptor Dimerization Steroid hormone signaling begins with the hydrophobic steroid diffusing through the plasma and nuclear membranes Hormone binds steroid receptor in nucleus the receptor alone can t bind to DNA and is inactive Upon binding receptor undergoes conformational change leading to displacement of Hsp90 and dimerization Steroid hormone receptor protein complex binds to DNA to regulate transcription which leads to a cellular response An Example HAT histone acetyltransferase modifies histones thereby de condensing chromatin activates transcription Thyroid Hormones Activate DNA bound receptor Thyroid hormone signaling begins with the thyroid hormone diffusing through the plasma and nuclear membranes The thyroid hormone binds to the thyroid hormone receptor in nucleus already bound to DNA but inactive Upon hormone binding receptor undergoes conformational change Thyroid hormone receptor complex regulates transcription An Example HDAC histone deacetylase inhibits chromatin de condensation inhibits transcription Overview of Paracrine Signaling Paracrine signaling molecules o Are secreted by a variety of cells o Act locally on target cells Types of paracrine signaling molecules o Gases diffuse across membrane have a short half life o Neurotransmitters o Peptide hormones and growth factors o Eicosanoids Types of paracrine receptors o Cell surface receptors o Common domains Extracellular ligand binding domain Membrane spanning domain Cytosolic catalytic domain Paracrine Signaling by Gases Nitric Oxide NO NO made by deamination of arginine Regulates many processes in many cells Short half life 5 10 seconds effects are rapid NO Relaxes Vascular Smooth Muscle Cells NO relaxes vascular smooth muscle cells VSMCs in arteriole walls o Endothelial cells that line blood vessels release a puff of Nitric Oxide that diffuses into underlying VSMCs causing them to relax o Leads to vasodilation and increased blood flow Nitroglycerin is converted to NO o Used for 100 years to relax blood vessels in patients with angina NO Target Guanylyl Cyclase Nitric Oxide stimulates Guanylyl cylase sGC which makes more cGMP cGMP activated multiple targets including cGMP dependent kinases and cGMP gated ion channels cGMP production is balanced by degradation to 5 GMP by phosphodiesterase PDE Viagra and Cialis inhibit PDE which blocks cGMP conversion to 5 GMP and leads to sustained blood flow in VSMCs Paracrine Signaling Neurotransmitters Neurotransmitter properties o Small hydrophilic molecules o Carry signals between neurons or from neurons to other target cells i e muscle cells Release is signaled by arrival of nerve