Bio 240 Chapter 11 Notes!
Bio 240 Chapter 11 Notes! Bio 240
Popular in General Genetics (Bio 240)
Popular in Biology
This 0 page Class Notes was uploaded by Izabella Nill Gomez on Thursday November 5, 2015. The Class Notes belongs to Bio 240 at University of Tennessee - Knoxville taught by Dr. Hughes in Summer 2015. Since its upload, it has received 25 views. For similar materials see General Genetics (Bio 240) in Biology at University of Tennessee - Knoxville.
Reviews for Bio 240 Chapter 11 Notes!
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 11/05/15
Biology 240 Chapter 11 Notes Semiconservative replication involves the synthesis of a new strand using the complementation of an old one Conservative replication complimentary polynucleotide chains are synthesized following newly created strands that come together and parents reassociate Dispersive replication parental strands are dispersed into two new double helices following replication Each strand has both old and new DNA Involves cleavage of parental strands during replication Most complex of the three theories 1958MeselsonStahl experimentgrowing E coli cells for many generations labeling N as the source of cell nutrients N 15 is more dense than N 14 Almost all N containing molecules had N 15 Sedimentation equilibrium centrifugation used to separate N 15 from N 14 N 15 was transferred to N 14 making all new synthesis of DNA with N 14 Cells replicate over generations After one generation isolated DNA fell in middle of centrifuge density intermediate semiconservative replication After 2 cell divisions DNA had one intermediate and one lighter band N 14 Proportion of lighter band increased over cell divisions lf DNA has dispersive replication all generations after t0 would be intermediate In each successive generation N 15N 14 would decrease and the band would become lighter not observed Experiment with broad bean in vila faba 1957Hughes Taylor Woods observed semiconservative replication Root tips were monitored for replication and labeled DNA with Hthymidine and autoradiography where applied cytologically pinpoints location of radioisotopes in a cell Dark grains identify newly synthesized DNA Arrested cells in metaphase after one generation After one replication both sister chromatids were radioactive with one old and one new strand After second replication in an unlabeled medium only one of the two are radioactive because half of parents strands were unlabeled At each point along the chromosome where replication is occurring strands of helix unwound and a replication fork was created Initially appears at a point of origin of synthesis and moves along DNA duplex as replication proceeds lf replication is bidirectional 2 forks are present migrating opposite ways Replication is the length of DNA that is being replicated following one initiation event In E coli OriC is the single origin where replication is initiated characteristic of bacteria because their chromosome is circular The entire chromosome is a replicon and replication is bidirectional DNA Polymerase I directs DNA synthesis Needed for all 4 dNTPs and template DNA Precursor dNTP contains 3 phosphate groups attached to 539 carbon As 2 terminal phosphates are cleaved in synthesis the last phosphate attached to 539 carbon is linked to 339 OHchain of elongation in 539339 direction by the addition of 1 nucleotide at a time to the 339 end DNA Pol I II and Ill cannot initiate DNA synthesis but can elongate an existing DNA strand primer and have the ability to polymerize in one direction pause reverse and excise in the other direction Pol l is present in greater amounts and can be more stable Removes primers during synthesis and lls primer gaps oca9 Holoenzyme active form of DNA Pol III core enzyme impacts the catalytic function of the holoenzyme Sliding clamp leader pairs with the core enzyme to facilitate the function of the sliding DNA clampdependent on ATP hydrolysis Links to core enzyme shapes as donut to encircle unreplicated DNA leads way in synthesis Processivity the length of DNA replicated by the core enzyme before detaching from the template One sliding clamp exists for one core enzyme Ori C in E coli is the origin of replication ATrich site less stable enhances helical unwinding DNaA initiator protein is responsible for initiating replication by binding to a region on 9mers at Ori C Undergoes change and associates with 13mers to destabilize the helix and expose single stranded DNA ssDNAbinding DNA helicase Binds to replication fork initiates replication opens up DNA helix Single stranded binding proteins SSBs bind to single strands of DNA to form a template Supercoiling tension occurs and coiling tension is created ahead of the replication fork DNA gyrase one of the topoisomerases relaxes this tension Synthesis of DNA begins with a type of RNA A short segment of RNA is synthesized by the DNA template through primase which is recruited to the replication fork by DNA helicase DNA Pol III added deoxy ribonucleotides initiating DNA synthesis Later an RNA primer is replaced by DNA under Pol l DNA Pol III synthesizes DNA in only the 539339 direction the other strand of DNA is 339539 Only 1 strand serves as the template for continuous DNA synthesis leading strand As the replication fork progresses many points of initiation are necessary on the opposite side of the template resulting in discontinuous DNA synthesis of the lagging strand Okazaki fragments are small fragments of newly synthesized DNA that include RNA primers converted into longer and longer DNA strands of higher molecular weight as synthesis proceeds Discontinuous synthesis requires enzymes to remove primers and unite Okazaki fragments into the lagging strand DNA Pol l removes primers and DNA ligase joins the fragments DNA is AT rich because of less H bondseasier to separate for DNA synthesis Both strands of DNA are synthesized simultaneously using one core enzyme for each Lagging strand forms a loop to do this A monomer of the enzyme will nd the completed Okazaki fragment and release the lagging strand A new loop is created etc To check for DNA errors DNA Pol I has exonuclease activity 339539 Proofreading Ligase de cient and proofreading de cient mutations can be lethal genetic analysis often uses conditional mutations expressed under one condition but not another ex temperature sensitive mutationsnot expressed at a permissive temperature but at a restrictive temperature is expressed with the mutant phenotype Differences between Eukarvotic and Prokarvotic replication Eukarya deal with more DNA Polymerases synthesize DNA 25x slower Multiple replication origins contained replication bubbles Origins in yeast autonomously replicating sequences ARSs consist of about 120 base pairs containing a consensus sequence nearly the same in all ARSs of 11 base pairs A prereplication complex preRC controls timing of replication at replication origins In 61 replication origins are recognized by the origin recognition complex ORC that tags the site as the initiation of replication Once synthesis begins preRC disassembles until the next 61 phase Distinguishes sites that have already been replicated Cell cycle kinases are essential at the initiation site to trigger proteins at the S phase The End result DNA unwinding stabilization DNA Pols at origins initiation of synthesis To accommodate the number of replicons eukarya have more DNA Pol molecules than bacteria Also use a larger number of different DNA Pol types about 14 different types Pol 0 enzyme synthesizes RNA primers on the leading and lagging strands Also adds 1020 complimentary deoxyribonucleotides Contains low processivity strength of association between enzyme and substrate the length of DNA synthesized before dissociating Once the primer is in place polymerase switching ve occurs where Pol 0 dissociates and is replaced by Pol extends primers on opposite strands of DNA has more processivity exonuclease activity proofreads 6 Pol 8 is on the leading strand Pol on the lagging These also do some DNA repair and recombination All 3 are essential for viability eukarya have Okazaki fragments 10x smaller than prokarya One of the major differences between prokaryoticeukaryotic DNA DNA is eukarya with DNAbinding proteins chromatin Consists of nucleosomes wrapped around histones Before synthesis nucleosomes must be modi ed to allow passage of replication proteins The nucleosome patterns are quickly reestablished for the new duplexes Old histones assemble with new ones ahead of the replication fork New nucleosomes are formed behind the replication fork Carried out by chromatin assembly factors CAFs Structured differences in chromosomes also exist Eukaryotic chromosomes are linear Problems arise double stranded ends of DNA molecules at the ends of linear chromosomes resemble doublestranded breasks DSBs that can occur when a chromosome becomes broken because of DNA damage Doublestranded loose ends can then fuse resulting in fusions and translocations because new DNA cannot be synthesized at the tips of singlestranded 539 ends Telomeres are linear chromosomes that help preserves chromosomes by creating inert ends to protect from degradation A 339 strand Grich strand is present on one of the two DNA strands making up each telomere and 539 strand Crich strand complimentary Grich 3 end lies in overhand becoming single stranded This allows it to create loops tloops based on 66 bands Makes DNA resistant to degradation The problem with the 539 end strand is that therea are no free 3 OH groups available to allow synthesis of DNA Gaps remain then on the newDNA strands at each successive round of synthesis shortening double stranded ends of the chromosome by the length of the RNA primer With each successive replication shortening in each daughter cell becomes more severe eventually extending beyond the telomere and potentially deleting genecoding regions The solution telomerase capable of adding more repeats to the Grich strand 539339 synthesis As a ribonucleoprotein contains a piece of RNA that guides attachment and serves as the template for DNA synthesis reverse transcription TERC and TERT aid in this The RNA enzyme base pairs with the overhang and extends beyond reverse transcriptase occurs extending the Grich lagging strand Then regular synthesis occurs The same happens to the Crich strand Telomerase is not usually active in somatic cells however Homologous recombination occurs at equivalent positions along 2 chromosomes with substantial DNA homology Possible exam questions 1 Difference between functions of DNA Pol l and Pol III DNA Polymerase III is the main polymerase of the replisome whereas DNA Polymerase l removes primers and lls in the gaps that are left 2 Which protein is responsible for unwinding DNA for replication DNA Helicase
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'