BIOLCHEM 415 1st Edition Lecture 33 Outline of Last Lecture I. DNA can be damaged by errors in replication of environmental effectsII. There are four types of replication errorIII. There are four ways by which the cell will repair DNAIV. Recombination is useful in many ways and can also be used for DNA repairOutline of Current Lecture V. Transcription is the first step in gene expressionCurrent LectureTranscription initial step in gene expressionRNA synthesis- Trascription- synthesis RNA from DNA template- catalyze by RNA polymerase- needs template (RNA complementary)- coding strand has same sequence as RNA- activated precursors (UTP, CTP, ATP, GTP)- divalent metal ion (Mg2+ or Mn2+)- strand grows from 5’ 3’- 3’ –OH attacks phosphate group to form phosphodiester linkage- no primer needed- had a 5’ triphosphate3 major RNA classesThese 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.- messenger RNA erodes into to generate protein- transfer RNA and ribosomal RNA play roles in translating mRNA proteinBacterial RNA polymerase composed of 5 subunits- holoenzyme = α2ββωσ subunits initiates RNA synthesis- core enzyme = α2ββ’ω subunits RNA elongation- β and β’ hold DNA being transcribed - Mg2+ at center of active site - holds everything in correct orientationPromoter sites- initiate transcription- DNA sequences that direct polymerase- -10 sequence (Pribnow box)- -35 sequence- σ subunits recognize - decreases polymerase affinity for rapid scanning- acts catalytically - E. coli has 7Open promoter complex- closed when DNA wound- open – RNA polymerase unwinds 17 bases of DNA to act as templateElongation- in the transcription bubble- intermediate = RNA-DNA hybridFidelity- transcription ~ 1error/104-5 bases- replication ~ 1error/1010 bases- RNA not inherited and it’s constantly remade so a little more error is okayTermination- Rho independent- hairpin stem loop structure followed by uracil residues- polymerase stalls- RNA product released- DNA double helix reforms- Rho dependent- requires protein Rho- binds to RNA sequence (C-rich or G-rich)- moves along RNA till contacts polymerase- transcription bubble dissociatesRNA- mRNA goes through little synthesis- rRNA and tRNA made as precursors- cleaved and modified after transcription- modifications important- structure diversityAntibiotics inhibit transcription- rifampicin- inhibits initiation blocks exit of nascent RNA - tb and meningitis- actinomycin- intercalates between bases of DNA double helix- prevents DNA template strandRegulation- control recruitment rate of RNA polymerase to promoter site- operon – regulating gene, operator, promoter, structural
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