BIO 326R 1st Edition Lecture 11Outline of Last Lecture I. Why does replication not continually initiatea. Hemimethylation and dnaAb. Cell sizeII. Proofreadinga. Base pairingb. Exonuclease activityc. Post synthesis mismatch repairIII. Terminating ReplicationIV. Transcriptiona. Stepsb. Types of RNAc. RNAPV. Initiationa. Promoter sequenceOutline of Current Lecture I. InitiationII. ElongationIII. Terminationa. Rho independentb. Rho dependentThese 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.IV. Side notes on transcriptionV. TranslationCurrent LectureInitiation- Promoter bindingo RNAP binds Sigma factor recognizes promoter Promoter strength is defined by the sequence Why different strengths?- Varied gene expression- Ex: Braun’s lipoprotein in E. Coli is highly expressed (600,000 copied needed)o RNAP-DNA complex= closed complex Double stranded DNA bound to RNAPo DNA unwinds= open complex RNAP bound to unwound DNA single strand- Transcription bubble-- ~12bpElongation- ~45 nucleotides/sequence- ~9 nucleotide RNA in the transcription bubble- Sigma factor falls off the RNAP and the transcript can elongate by the core RNAPo Sigma factor falls off, elongation continues with the core enzyme, and the transcription bubble moves with RNAP- Proofreadingo RNAP does have proofreading activityo If it incorporates an incorrect base, it will pause and remove ito Error in 1 in 10^5 nucleotidesTermination- Rho independento Most prevalento Forms a stem loop Stem rich in G/C base pairs because they are stronger than A/T pairs and thus make a stable loopo Uracil repeat tail on strand downstream from the stem loop Weak basepair with DNA Causes RNAP to fall off of the DNA- Rho dependento Rho protein requiredo Hexameric protein that binds mRNAo ATPase activityo Moves along RNA until the RNAP siteo Binds to RNAP, unwinds DNA/RNA hybrid, causes RNAP to dissociate from DNAo Less prevalent because of use of ATP Not energetically favoredTranscription Side Notes- Bacterial mRNAs are often polycistronico One mRNA encodes multiple proteins, multiple genes (operons) Operons= polycistronic mRNAs, coding 2-3 genes- RNA half liveso They varyo Average in bacteria is about 3 minutes This is because their environment is unstable and they must change internally quickly to adapt to their external environmento Average in eukaryotes is about 10 hours This is because environment is very stableTranslation Intro- Transcription and translation are coupled in bacteria- ~90% of E. coli energy production is used for translation- ~30-60% (more so 60%) of all macromolecules in E. coli are involved in
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