BCHM 3050 1st Edition Lecture 19 Outline of Last Lecture I Triple Stranded DNA II Prokaryotes vs Eukaryotes III Transposons IV Comparing Genome Segments from Selected Organisms V General Characteristics of DNA Replication VI Meselson and Stahl VII Replication Origins VIII Summary of DNA Replication Outline of Current Lecture I Steps in DNA Synthesis a Initiation b Elongation c Termination II Structure of DNA Polymerase Dimer III Dimeric Function of DNA Polymerase IV Overview of the E coli Replisome V Termination of DNA Replication in Prokaryotes VI Ends of DNA are not completely replicated These 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 VII Telomere Structure and Function Current Lecture I Steps in DNA Synthesis a Initiation i 1 Origins of replication bind to initiation factors ii 2 Helicase binds iii 3 Topoisomerase binds and prevents supercoiling occurs almost at same time as 2 iv 4 ssBP v No protein can work alone it s a concerted effort vi Grand finale of Initiation is the helicase unwinding the DNA strands vii Initiation Factors DnaA proteins viii Bring helicase to origin of replication ix Helicase DnaB proteins x Helicase needs energy from ATP to break bonds xi Some mode of tension exists all the time in DNA xii Topoisomerases bind on either side of the origin and introduce a small cut in DNA that helps to prevent tangling supercoiling in DNA relax stress xiii ssDNA single stranded binding proteins prevent strands of DNA from coming back together b Elongation i Elongation new 5 3 DNA strand is created ii Primase NEEDS a primer to start synthesis flaw of primase primer small RNA nucleotide chain iii Primase is a type of RNA polymerase iv Gaps between lagging strands are filled by DNA ligase v DNA polymerases are just named with numbers in the order of their discovery vi DNA polymerase II is involved in proofreading and DNA repair vii DNA polymerase 3 is also involved in DNA repair c Termination i Specific termination proteins and termination sites similar to palindromes ii Termination binding proteins bind to termination sites on opposite side of the DNA loop II Structure of DNA Polymerase Dimer a DNA polymerase functions as a dimer structure b Alpha is the main part of the dimer c Alpha brings in nucleotides and extends DNA d Beta is a sliding clamp holds nucleotides in place and prevents DNA from escaping from the polymerase increases processivity decreases the chances that DNA and the DNA polymerase will let go of each other e Upsilon fixes mistakes right there but if it missed the mistake then DNA polymerase II will come in and try to fix it f The clamp needs ATP to hold in the DNA g Processivity is the frequency with which an enzyme dissociates from the template during DNA replication h Upsilon cuts out portion and sends it back Editing Mode III Dimeric Function of DNA Polymerase a Don t know as much about termination b Leading and lagging strands must end at the same time c One half of the dimer will build the leading strand and one half will build the lagging strand IV Overview of the E coli Replisome a One side makes lagging strand and other makes leading strand but they move together and are moving in opposite directions so they loop back together b DNA polymerase 1 is the purple structure farthest to the right the two purple structures to the left are DNA polymerase III c Replisome consists of what you see at the replication fork alone i Dimer of poylmerase III ii Helicase iii Primase putting down primer iv Single stranded bind protein d NOT found at replication fork i DNA ligase ii DNA polymerase I V Termination of DNA Replication in Prokaryotes a Prokaryotes only have one origin of replication while eukaryotes have multiple b Replication is always bi directional 2 lagging strands and 2 leading strand from a single origin of replication c Everything falls off at the point of termination VI Ends of DNA are not completely replicated a Polymerase needs a primer to start on cannot build DNA that s de novo b There will always be a gap at the end of a new strand that cannot be filled because there is no primer there for polymerase to add nucleotides c This causes DNA to get shorter and shorter with each DNA replication process aging due to shortening of DNA d We have adapted to beat this shortening by the use of telomeres e Telomeres loose ability to function though after a long time VII Telomere Structure and Function a Telomeres are sequences present at the very end of chromosomes DNA and can see them light up at the ends b Every time a cell divides a little bit of the telomeres are lost c Cancer cells are an exception and maintain telomeres survive longer and reproduce much faster than normal cells take over d Stem cells also do not divide as much and must be maintained so their telomeres are never lost e Process of aging lose telomeres over time f Telomere is a sequence of DNA g Telomerase is an enzyme that helps to fill in the gaps h Dolly was the first true animal clone
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