BBMB 405 1st Edition Lecture 38 Outline of Last Lecture XVII Chapter 32 The control of gene expression in eukaryotes C The control of gene expression can require chromatin remodeling D Transcription factors bind DNA and regulate transcription initiation Outline of Current 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 Current Lecture XVII Chapter 32 The control of gene expression in eukaryotes E Eukaryotic Gene Expression can be controlled at posttranscriptional levels 1 Biogenesis of miRNAs and formation of RISC a microRNA needs to be cleaved cleavage along dsRNA b Create 21 to 25 nucleotides c In duplex contains 3 end overhands d Duplex unwound and one strand is chosen as a guide to form silencing complex e 2 Dicer and Argonaute Ago recognize RNA ends 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 3 Posttranscriptional silencing by RISC a RISC binds to sequences in 3 UTR of mRNAs that match miRNA b Complementarity is required only in seed or positions 2 to 8 miRNA sequence c Some mRNAs have more than one miRNA target sequences d e Complete complementarity between guide RNA and mRNA leads to endonucleolytic cleavage most common in siRNA pathway f Mismatches between guide RNA and mRNA will lead to translational repression or destabilization of mRNA most common in miRNA pathway 4 miR 206 represses estrogen receptor a Estrogen receptor ER mRNA is susceptible to post transcriptional regulation by miRNA 206 b Breast cancers have low levels of miR 206 miR 206 levels are inversely related to levels of ER mRNA c Introduction of miR 206 into breast cancer cells inhibits cell growth in a doseand time dependent manner it is a potential therapeutic but RNA is difficult to deliver XVIII Chapter 33 Sensory Systems A A wide variety of organic compounds are detected by olfaction 1 How do we perceive the physical world a Stimuli leads to detection of physical event b Signals are sent through receptors expressed in sensory neurons specific receptors have specific signals c Signals are transmitted to central nervous system by specific neurons 2 Smell Detection of organic compounds by olfaction a Odorants stimulate smell b Properties of odorants volatility easier transport to olfactory system small organic compounds generally smaller than 300 Da shape of molecule determines interactions with receptor 3 Stereoisomers can have significantly different olfactory properties a Chemically indistinct except for shape example R carvone smells like spearmint and S carvone smells like caraway b c Likely interact differently with protein receptor suggesting that protein receptors recognize odorant shape 4 Olfaction is mediated by receptors in nasal epithelium a Transmembrane receptors are found in cilia and synapses of sensory neurons G protein coupled receptors GPCRs b 5 Olfactory receptors OR a Rats contain more than 1000 genes expressing olfactory receptors humans have about 350 but about 500 pseudogenes or nonfunctional versions b Each OR can recognize several different odorants to different degrees c Only one type expressed per olfactory neuron combinatorial activation enables differentiation between odors 6 Genetic variations in OR genes may cause change taste perception a SNP identified in cilantro haters is located near cluster of olfactory receptors b One of nearby genes OR6A2 detects aldehydes that make cilantro smell soapy
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