BBMB 405 1st Edition Lecture 39 Apr 27 Outline of Last Lecture XVII Chapter 32 The control of gene expression in eukaryotes E Eukaryotic Gene Expression can be controlled at posttranscriptional levels XVIII Chapter 33 Sensory Systems A A wide variety of organic compounds are detected by olfaction Outline of Current Lecture XVIII Chapter 33 Sensory Systems A A wide variety of organic compounds are detected by olfaction B Taste is a combination of senses that function by different mechanism C Touch includes the sensing of pressure temperature and other factors Current Lecture XVIII Chapter 33 Sensory Systems A A wide variety of organic compounds are detected by olfaction 1 G protein coupled receptors GPCR a Not in prokaryotes activated by GTP rhodopsin was the first GCPR found b Largest and most diverse class of membrane receptors c Each GPCR recognizes specific set of signals d GPCR signals can be small molecules peptides proteins or light energy e GPCRs transduce signal to trigger signaling cascade These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute f Approximately 40 of prescription drugs target GPCRs 2 GRCRs are coupled to G proteins a b The odorant is the agonist which binds to the 7 transmembrane domain receptor c Inverse agonist inverse biological response d G protein binds to GDP and when nucleotide exchange subunits fall off and GTP binds to adenylate cyclase or other transmembrane protein to start cascade e To remove GTP from adenylate cylase need to hydrolyze GTP 3 Olfactory signal transduction cascade a GPCR recognize small less than 3 Da organic molecules epithelium contain receptors b GPCR agonist binding activates G protein c G protein activates adenylate cyclase d cAMP product of adenylate cyclase activates ion channels e Action protential created signal translated into action potential that leads to neuronal signaling cascade B Taste is a combination of senses that function by different mechanisms 1 Taste detection of compounds by gustation and olfaction a Stimulant Tastants b Sweet and bitter tastants are diverse sweet carbohydrates small derivatives proteins bitter alkaloids often toxic c Other tastants are limited in number salty and sour are usually ions umami is glutamate or aspartate d 2 Taste buds contain taste receptors a Taste receptors are GPCRs T1R family sweet and umami receptors T2R family bitter receptors Often coupled with G protein gustducin which is expressed in taste buds b Taste also depends on ion channels sodium channels for salty and hydrogen channels for sour c d Nerve fiber is connected to brain contains about 150 cells 3 Bitter receptors a Some people taste bitter more than others variations in bitter receptor expression may affect how people perceive tastes Supertasters may express T2R38 can taste PROP b Is bitter just bitter Each neuron in taste buds expresses many bitter receptors more difficult to discriminate identity of tastant c Not as many neurons in better receptors 4 Sweet and Umami receptors likely activated as heterodimers T1R1 T1R2 T1R3 C Touch includes the sensing of pressure temperature and other factors 1 Touch Detection by somatosensation a Perception formed from many modalities Touch pressure flutter vibration itch tickle Temperature hot cold Pain sharp dull deep b Stimuli can be mechanical thermal or chemical c Capsaicin has vanilyl group used in receptor 2 Nociceptors Pain perception neurons a Nociceptors are sensory neurons that respond to potential tissue damage by sending signals to pain processing centers of spinal cord and brain b Vanilloid receptor 1 is a TRP family TRPV1 non selective ion channel activated by chemical thermal and acid stimuli 3 Structure of TRPV1 receptor gates won t let ions through capsaicin bound opens the gates and turns pain receptor on but only slightly double knot toxin irreversibly activates and is used as therapy to dull the receptors over time
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