BBMB 405 1st Edition Lecture 40Outline of Last Lecture XVIII. Chapter 33: Sensory SystemsA. A wide variety of organic compounds are detected by olfactionB. Taste is a combination of senses that function by different mechanismsC. Touch includes the sensing of pressure, temperature, and other factorsOutline of Current Lecture XVIII. Chapter 33: Sensory SystemsD. Hearing depends on the speedy detection of mechanical stimuliE. Photoreceptor molecules in the eye detect visible lightXIX. Chapter 35: Molecular MotorsA. IntroductionCurrent LectureXVIII. Chapter 33: Sensory SystemsD. Hearing depends on the speedy detection of mechanical stimuli1. Hearing: Detection of vibrations by auditiona. Sound waves of 200 to 20,000 Hz is the stimulantb. Mechanical stimulus (like modalities of touch)c. Detection of sound and sound locationThese 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.d. located in inner ear, coclia2. Mechanical stimulation of hair cells causes changes in membrane potentiala. Movement of hair bundle acts on ion channels directly: membrane depolarization, leads to rapid responseb. Tension along tip link (extracellular filaments that connect stereocilia) increases the depolarizationc.d.e. From -200 to 0: Tension decrease and from 0 to 200: tension increase3. Touch and hearing rely on mechanoreceptor proteinsa. Mechanosensitive ion channels: mechanical deformations of cell membrane switch ion channels from closed to openb. Made of ankyrin repeats: potential gating springs4. Model for mechanosensitivity: No mechanoreceptor potential C (nompC) gene; when gene deleted mechanoreceptor doesn’t work5. Recent advances in our understanding of touch receptorsa. “Piezo2 is major transducer of mechanical forces for touch sensation in mice”b. Piezo2 is expressed in sensory neurons, innervate skin of mice and involved in low-threshold mechanosensitivity (light touch)c. Loss of function results in loss of touch sensationd. Loss of function has not effect on pain receptors (nociceptors)E. Photoreceptor molecules in eye detect visible light1. Sight: Detection of visible lighta. Rod cells express Rhodopsin: GPCR recognize light, opsin linked to chromosome 11-cis-retinal, retinal is aldehyde form of vitamin Ab. Cone cells express rhodopsin homologs: Absorb light at different wavelengths2. Rod cells detect dim lighta. Light absorption causes isomerization of cis to transb.c. Retinal isomerization causes rhodopsin conformational change3. Signal transduction by rhodopsina. Occurs on millisecond scaleb. Rhodopsin activation leads to transducing nucleotide exchangec. Activated transducing activates phosphdiesterase that converts cGMP to GMPd. Decrease in cGMP levels lead to reduction in ion flow through cGMP-gated ion channele. Membrane hyperpolarization and neuronal signaling resultsf. Closing of cGMP-gated ion channel and Ca2+ efflux leads to guanylatecyclase activation (inhibited by Ca2+) and restoration to initial stateg.4. Cone cells detect brighter light in colora. Types of cone cells: L-cones: long wavelengths (red), M-cones: medium wavelength (green), S-cones: short wavelength (blue)b. Each type of cell contains different pigmentc. Associated with photopsinsd. Three different sites cause changes in what wavelength is detected5. Red-green color blindnessa. Highly similarity between red and green photoreceptors (98% identical, including introns and UTRs)b. Susceptible to unequal homologous recombinationc. 5% of human males have this conditiond.XIX. Chapter 35: Molecular MotorsA. Introduction1. Examples: E. coli chemotaxing to sugar, white blood cell chasing bacteria, human heart muscle cell beating, movement of animal2. Three major families of eukaryotic motor proteinsa. Motor: device that converts energy into mechanical workb. Motor domains: “Head” domains bind ATP and trackc. Actin motor: myosind. Microtubule motor: kinesin and dynein3. Cytoskeletal motor proteins utilize a “track”a. Kinesin pulls vesicle along cytoskeletal microtubule filamentb. Myosin molecules form thick filament at center of actin filamentsc. Cytoskeletal fibers are tracks: actin filaments,
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