BOLOGY 107 Lecture 27Outline of Last Lecture I. DNA Structurea. Watson and Crickb. Genetic Materialc. DNA ReplicationOutline of Current Lecture II. DNA Replicationa. Polymerasesb. Proofreading c. Eukaryote problemIII. Gene Expressiona. “Central Dogma”b. Transcription Current LectureDNA Replication1) Polymerasesi) Require template (old DNA strand)ii) Samples nucleotide triphosphate until the proper hydrogen bonds formiii) Attaches nucleotide to the 3’ OH of previous base, releases a pyrophosphate (2 phosphates)b) Primase (RNA polymerase)i) Primase lays down RNA primer(1) Builds a short strand of RNAc) DNA Polymerase III (Pol III)i) Starts DNA off of RNA primerii) Builds from 5’ to 3’(1) Two strand of old DNA become separate, for “leading” and “lagging” strands(a) Leading strand matches the direction needed for replication, replicated in a continuous strand(b) Lagging strand is opposite direction for replication, replicated in sectionsThese 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.(i) Okazaki fragments- sections of DNA curved to replicate in the proper direction, “leapfrogged”1. Need cleaned up from RNA primers to start each jumpd) DNA Polymerase I (Pol I)i) Removes RNA fragments and replaces them with DNA fragmentse) DNA Ligasei) Bonds spaces in DNA where chain stops 2) Proofreadinga) Contemporaneous with synthesis and subsequent to synthesisb) If Pol III places improper base, it can step back and attach proper basei) Sensed by a distortion in helic shapec) Mistake can be cut out by Pol I laterd) Change becomes permanent if not corrected before DNA is replicated again3) Eukaryote problema) Linear DNA has ends, because the RNA primer is needed to start the new strand, DNA is cut from the front each replicationi) Telomere- stretch of repetitive sequence at the end of a chromosomeii) Telomerase extends repetitive sequence using its own RNA templateGene Expressionb) Small change in DNA can lead to a large phenotype change4) “Central Dogma”a) Information flows from DNA to RNA to proteinsi) Transcription- DNA information to RNAii) Translation- RNA information to proteins(1) In bacteria, happen in the same place and time(2) In eukaryotes, different place and time(a) Transcription- nucleus, translation- cytoplasmb) Universal system used by all cells5) Transcription a) Uses DNA as a templatei) RNA polymerase makes RNA 5’ to 3’ based off of DNA, detaches at bases, DNA re-associates with other strand(1)
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