Chapter 8 - Chapter 8 RNA Transcription and Processing RNA...

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Chapter 8: RNA Transcription and Processing I) RNA A) Pulse-chase experiment—rapid turnover of RNA 1) Infected bacteria fed radioactive uracil (pulse) 2) After short incubation, radioactive uracil washed away and replaced with non-radioactive uracil (chased) 3) As RNA breaks down only unlabeled precursors available to synthesize new RNA molecules 4) Showed RNA has short lifetime 5) In eukaryotes, shortly after the pulse, most uracil in nucleus, after chase most in cytoplasm B) Properties of RNA 1) Usually single stranded more flexible and greater variety shapes (can do intramolecular base pairing) 2) Ribose sugar in nucleotides 3) Has hydroxyl group at 2’ carbon atom helps facilitate RNA action 4) Bases: adenine, guanine, cytosine, uracil a) Uracil binds with A b) Also capable of binding with G only during RNA folding (not transcription) 5) Ribozyme—RNA that can catalyze biological reactions C) Classes of RNA 1) Messenger RNA (mRNA)—intermediary that passes info from DNA to protein 2) Functional RNA—does not code information to make a protein a) Transfer RNA (tRNA)—bring correct amino acid to mRNA in translation b) Ribosomal RNA (rRNA)—major components of ribosomes, guide assembly of the amino acid chain by the mRNAs and tRNAs c) Small nuclear RNAs (snRNAs)—only in eukaryotes, further process RNA transcripts, form splicosome that removes introns from mRNAs d) MicroRNAs (miRNAs)—in eukaryotes, regulate amount of protein produced e) Small interfering RNAs (siRNAs)—in eukaryotes, help protect integrity of genomes, inhibit production of viruses prevent spread of transposable elements II) Transcription—synthesis of RNA from DNA A) Overview 1) Two strands of DNA separate locally, one is template for RNA synthesis in any one gene 2) Ribonucleotides form stable pairs with complementary bases in the template, positioned by RNA polymerase 3) Growth occurs in the 5’ to 3’ direction, nucleotides always added at 3’ growing tip B) Nontemplate strand is the coding strand—has same sequence as the transcribed RNA C) Stages of transcription in PROKARYOTES 1) Initiation a)
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