FA2011lecture5 - Bird’s eye view of the flow of...

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Unformatted text preview: Bird’s eye view of the flow of gene3c informa3on (gene  ­> mRNA  ­> protein) introns exons Structural elements of DNA C T G A base + deoxyribose + phosphate = nucleo5de Double helix structure of DNA: an3 ­parallel strands with “complementary” sequences 5  ­ GCTAATCAA  ­ 3 3  ­ CGATTAGTT  ­ 5 ! DNA replica3on: strands separate, new complementary strand synthesized using old strand as template “Central Dogma”: informa3on flows from DNA to mRNA to protein Transcrip3on: one strand of DNA serves as template for synthesis of a complementary RNA strand (ribose instead of deoxyribose; U instead of T) Transla3on: triplet gene3c code directs addi3on of one amino acid at a 3me as directed by mRNA sequence to build a polypep3de chain Key aspects of the gene3c code •  triplet codons specific amino acids •  3 codons specify STOP: –  UAA, UAG, UGA •  partly redundant code  ­ some amino acids specified by more than one triplet Klug textbook, Fig. 12 ­7 pg. 247 (Almost) all cells have the same gene3c informa3on, but they don’t all use it the same way: gene regula3on •  Every gene is expressed only at certain 5mes in certain cells in certain amounts •  For example… pancrea5c cell makes insulin pancrea5c cell doesn t re5nal cell doesn t (even though it has the gene) re5nal cell makes re5nal pigment Gene regula5on can occur at all of these stages in eukaryo5c cells; we will focus on steps 2, 5 and 6 Promoter: •  •  •  •  Region of gene lying upstream of coding sequence that is necessary for transcrip5on Acts “in cis” to regulate transcrip5on (on same DNA strand as gene being regulated) Composed of discrete elements, typically including TATA, CCAAT and GC boxes Types, number, and posi5ons of these elements varies from gene to gene Summary of effects on transcrip5on levels of point muta5ons at every possible posi5on in the promoter region of the beta globin gene: altera5ons in TATA, CCAAT and GC boxes markedly reduce transcrip5on Enhancers and Silencers: •  •  •  Modulate basal transcrip5on levels achieved through ac5on of promoter Like promoters, act in cis (on same DNA molecule as gene being regulated) Unlike promoters, act at a distance from the gene and their posi5ons are flexible (can move them around and they s5ll work) Promoters, enhancers and silencers serve as binding sites for sequence ­specific DNA binding proteins that regulate transcrip3on For example, regulatory region upstream of human metallothionein IIA gene contains 4 promoter elements (TATA box, GC box, BLE, ARE) and 2 enhancer elements (MRE, GRE) that each bind to a different DNA binding transcrip5on regulatory protein How can mul3ple DNA binding proteins work together to regulate transcrip3on? •  Promoter elements mediate assembly of “pre ­ini5a5on complex” (PIC) of basal/ general transcrip5on factors, which recruits RNA polymerase (Pol II in this drawing) •  Proteins bound to enhancer elements interact with basal transcrip5on factors to influence assembly of PIC RNA interference (RNAi): a newly recognized mode of gene regula3on •  Mechanism s5ll a very ac5ve area of inves5ga5on •  Expression of many genes regulated by this mechanism •  May be important for defense against viral infec5on •  VERY USEFUL TOOL FOR GENETICISTS! •  Also very promising avenue for treatment of diseases caused by gene misregula5on, e.g. cancer dsRNA (~21 ­24 nucleo5des) RNAi: short double ­ stranded RNA molecules block gene expression via mul3ple mechanisms (21 ­24 nucleo5des long) Single ­stranded small RNA, pairs with complementary mRNA sequences to guide RISC complex to specific transcripts ...
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This note was uploaded on 01/16/2012 for the course BICD 100 taught by Professor Nehring during the Fall '08 term at UCSD.

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