BIOL 4610 1st Edition Lecture 6 Outline of Current Lecture I. Methylation of DNAII. Post-transcriptional ControlCurrent LectureMethylation of DNA – another epigenetic modification Similar to histones, when we methylate DNA we decrease transcription This happens on cytosine Opposite side of methyl group forms the hydrogen bond w Guanine Important in development DNA methylation represses transcription -By “masking” a TF binding site Transcription factors recognize promoters- specific DNA sequences of ~10bp in length Ezh2- histone methylase DNMT- DNA methyl transferaseChapter 8 – 8.4. Post-transcriptional Gene ControlTo control translation after transcription, can use ~20-26bp short RNAs:1) Those that repress translation of specific mRNAs (called microRNAs or miRNAs)1) Small ribosomes2) Those that cause mRNA degradation (termed short interfering RNAs or siRNAs). 2) MicroRNAs or miRNAs: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.1) These are present as genes (>1000)2) Can be transcribed like any other gene (have promoters, enhancers etc.)3) Primary microRNA (70-80bp in length)4) Forms a pseudo-complementary (imperfect) binding5) The folding back on itself allows it to be bound in the nucleus by a protein called DGCR8 (double stranded RNA binding protein)6) Drosha- ribonuclease that cuts part of microRNA2) RNA Interference (siRNA) – need a perfect match in the 21-23bp long siRNA. – Come from viruses or are manufactured in lab– Rather than binding to 3’ translating region, they bind to the coding area of mRNA. Need perfect match of base pairs to get this to work.– Argonaute gets activated and cuts mRNA. (only works if perfectly complementary). Cuts into pieces of ~10bp in length In nucleus we have genes that code for miRNADrosha does some cutting and gets exported out into nucleusCan also have siRNA, made artificially or from a virus.Both mRNA and siRNA must be cleaved by a dicer. Once cleaved, they get loaded into RISC complex.Is RNA is mismatched, miRNA – 3’ UTRIs perfect complementarity – siRNA- mRNa gets chopped upBottom line à decreases protein
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