Exam 3 Study Guide - Chapter 7 DNA v RNA structure RNA DNA...

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Chapter 7 DNA v. RNA structure RNA DNA Sugar Ribose Deoxyribose Base Pairing A-U G-C A-T G-C Structure Single Stranded Double Helix Form Alpha Beta Handedness Right Right Pitch 25 Å 34 Å Diameter 23 Å 20 Å Roles of RNA mRNA – codes for proteins (central dogma DNA-RNA-protein) rRNA – forms core of ribosome structure, catalyzes protein synthesis miRNA – regulates genes expression tRNA – adaptors between mRNA and amino acids other – RNA splicing, gene regulation, telomere maintenance, etc. RNA polymerase Catalyzes linkage of ribonucleotides Does not need a primer; synthesized 5’ to 3’ Proofreads by backtracking (only one active site) Unwinds template in bacteria DNA polymerase Has second active site for proofreading Binds to a primer to begin replication Uses sliding clamp/clamp loader Bacterial Transcription Haloenzyme – RNA polymerase + Sigma factor Initiation: haloenzyme binds to promoter o The start-site is designated by +1 o Defined by -35 and -10 positions (upstream) Elongation: RNA strand grows o Sigma factor is released during elongation o RNA polymerase synthesizes RNA Termination: release of polymerase and RNA strand Eukaryotic Transcription There are three types of RNA polymerase o Type I: for most rRNA genes o Type II: protein coding genes, miRNA genes, noncoding RNAs o Type III: tRNA, 5s rRNA genes, genes for many other small RNAs Promoter sequence in most cases is the TATA box located at -25
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Transcription factors must bind before replication begins o The order differs for each promoter o TFIID binds at promoter with TATA-Binding Protein subunit (TBP) o TFIIH unwinds strands and phosphorylates RNA poly-A tail 3 Bacterial v. Eukaryotic Transcription Bacterial cells contain a single RNA polymerase, whereas eukaryotic cells have three Bacterial RNA polymerase can initiate transcription without the help of additional proteins, whereas eukaryotic RNA polymerases need general transcription factors.
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