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U-M BIOLOGY 172 - Lecture 6

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Lecture 6I. DNA ReplicationA. DNA pol III has proofreading ability and will correct most mistakes as they occur (mismatch base pairing)B. Telomerase1. active in cells that need to divide2. extends the length of telomeresC . Replication in Prokaryotes v. Eukaryotes1. because prokaryotes have a single circular chromosome, their chormoseom has no termninal ends2. Eukaryotes have several lineal chromosome, their chromose have terminal ends called telomeresII. Telomeres and TelomeraseA. Telomeres1. regions of repetitive DNA nucleotide sequences in eukaryotic linear chromosomes2. protect the ends of chromosome from deterioration and damage 3. each round of replication the telomeres are shorten(?)4. G- rich sequence present on the end of the DNA base pairs with a complemeney RNA present in telomeraseB. Telomerase(aging and cancer)1. required by some cells (stem cells, and germ line cells) to maintain proper length of telomeres2. the genes encoding telomerase is inactive in other cell types3. When DNA polermase 1 removes the last primer there is no way to add a dntps because because there is no 3’ end available 4. Functionsi.extends the 3’ end so that a primer can be added to the end and DNA synthesis happens5. Becomes active once bound to the 3’ end of the G-rich overhang6. does not require a template to begin DNA synthesus because the enzyme has a small RNA template bound7. Needs to be long wnough that no portion of the gene is lost during replicartionIII. Proofreading and Repair of DNAA. errors are rare in DNA ReplcationB. DNA polyermesa proofreads nucleotide againist the templatei. mismatches can also be ideintifeid by other enxymes and be fixed* Genes specify the sequence of RNA and ultimaltey the primary structure of proteinIV. Central Dogma - the journey from DNA to RNA to ProteinsA. Transcription1. DNA to RNA2. Basic Featurei. synthesis of RNA using DNA as a template ii. Catalyzed by RNA polymeraseiii. Occurs in specific portion of DNA (genes)iv. Occurs in the nucleus of a eurkayote and in the nuclear region(cytosol) in a prokaryotev. synthesized 5’ to 3’vi. Only one strand of DNA is used as the template vii. the strand not used as the template is the coding strand because it will be the same as the new RNA strand3. Initiationi. starts at a promoter sequence (TATA box)ii. Transcritpion Factors(Proteins)bind to the promotor region and attract RNA Polymerase iii. RNA polymerase unwinds DNA and begins to synthsizeDNA POLYMERASE RNA POLYMERASETemplate needed Template needed5’ to 3’ 5’ to 3’3’ OH primer No primer neededATGC AUGCProofreading ability No proofreading ability4. Elongationi. RNA polermearse adds RNA nucleotides to the 3’ endii. the 3 OH’of the growing strand attacks the high energy of the triphostfate bond of the new nucleotide to get energy to drive the reaction B. Termination1. RNA polermase stops adding ribonuleotides(rNTPS) and the RNA chain is released2. occurs at a specific Termination sequence3. Often triggered by formation of a RNA hairpin loop(proks)(?)V. RNA ProcessingA. Prokaryotes use RNA immediaelty in translation 1. transcription and translation happens at the same time in prokaryotesB. Eukaryotes must process the pre mRNA( both introns and exons) before the translation occurs1. addition of the 5’ cap i. the ribosme recognizes mRNA and binds to the 5’cap2. addition of the poly A tail to the 3’ endi. helps mRNA get exported from the nucleus to the cytoplasm for translation3. RNA splicing by splicosomesi. removal of introns( non-coding strands)ii. snRNPS(small nuclear ribosome nucleoproteins)a. bind to at the exon-intron boundaryb. several snRNPS and proteins assemble to for a spliceosomes1) the RNA breaks at adenine4. all that will be left is Exons which is used in translationC. modification help stabilze the RNA and help promote transaltion*Introns allow for exon shuffling or alternativesplicing. This allows usto make protein isoformsor more than one proteinfrom a single mRNA transcript. Hugelyimportant!!!!


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