BBMB 405 1st Edition Lecture 39 Apr 27Outline of Last Lecture XVII. Chapter 32: The control of gene expression in eukaryotesE. Eukaryotic Gene Expression can be controlled at posttranscriptional levelsXVIII. Chapter 33: Sensory SystemsA. A wide variety of organic compounds are detected by olfactionOutline of Current Lecture XVIII. Chapter 33: Sensory SystemsA. A wide variety of organic compounds are detected by olfaction B. Taste is a combination of senses that function by different mechanismC. Touch includes the sensing of pressure, temperature, and other factorsCurrent LectureXVIII. Chapter 33: Sensory SystemsA. A wide variety of organic compounds are detected by olfaction1. G protein-coupled receptors (GPCR)a. Not in prokaryotes, activated by GTP, rhodopsin was the first GCPR foundb. Largest and most diverse class of membrane receptorsc. Each GPCR recognizes specific set of signalsd. GPCR signals can be small molecules, peptides, proteins or light energye. GPCRs transduce signal to trigger signaling cascadeThese 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 GPCRs2. GRCRs are coupled to G proteinsa.b. The odorant is the agonist which binds to the 7 transmembrane domain receptorc. Inverse agonist: inverse biological responsed. G protein binds to GDP and when nucleotide exchange subunits fall off and GTP binds to adenylate cyclase (or other transmembrane protein) to start cascadee. To remove GTP from adenylate cylase need to hydrolyze GTP?3. Olfactory signal transduction cascadea. GPCR recognize small (less than 3 Da) organic molecules, epithelium contain receptorsb. GPCR agonist binding activates G proteinc. G protein activates adenylate cyclased. cAMP product of adenylate cyclase activates ion channelse. 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 mechanisms1. Taste: detection of compounds by gustation (and olfaction)a. Stimulant: Tastantsb. 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 aspartated.2. Taste buds contain taste receptorsa. 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 budsb. Taste also depends on ion channels: sodium channels for salty and hydrogen channels for sourc.d. Nerve fiber is connected to brain, contains about 150 cells3. Bitter receptorsa. Some people taste bitter more than others: variations in bitter receptor expression may affect how people perceive tastes, “Supertasters” may express T2R38, can taste PROPb. Is bitter just bitter? Each neuron in taste buds expresses many bitter receptors, more difficult to discriminate identity of tastantc. Not as many neurons in better receptors4. Sweet and Umami receptors likely activated as heterodimers: T1R1, T1R2, T1R3C. Touch includes the sensing of pressure, temperature, and other factors1. Touch: Detection by somatosensationa. Perception formed from many modalities- Touch: pressure, flutter, vibration, itch, tickle- Temperature: hot, cold- Pain: sharp, dull, deepb. Stimuli can be mechanical, thermal or chemicalc. Capsaicin has vanilyl group used in receptor2. Nociceptors: Pain perception neuronsa. Nociceptors are sensory neurons that respond to potential tissue damage by sending signals to pain-processing centers of spinal cord and brainb. Vanilloid receptor 1 is a TRP family (TRPV1) non-selective ion channel activated bychemical, thermal, and acid stimuli3. 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
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