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NOT FOR SALE OR DISTRIBUTION. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning,PART LLC © JonesII & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION DNA Replication © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION and NOTRecombination FOR SALE OR DISTRIBUTION © Jones & BartlettCHAP Learning,TER 9 ReplicationLLC Is Connected© Jonesto the Cell& Bartlett Cycle Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION CHAPTER 10 The Replicon: Initiation of Replication CHAPTER 11 DNA Replication © Jones & Bartlett Learning,CHA LLCPTER 12 Extrachromosomal© Jones &Replicons Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONCHAPTER 13 HomologousNOT and FOR Site-Specific SALE OR DISTRIBUTION Recombination CHAPTER 14 Repair Systems © Jones & Bartlett Learning, LLC CHAPTER 15© Jones Transposable & Bartlett Elemen Learning,ts and LLC Retroviruses NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION CHAPTER 16 Somatic Recombination and Hypermutation in the Immune System © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Laguna Design/Science Source. 227 9781284104646_CH09_227_244.indd 227 01/02/17 5:09 PM © Jones & Bartlett Learning LLC, an Ascend Learning Company. 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CHAPTER 9 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Replication Is Connected © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC to theNOT Cell FOR SALE ORCycle DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Edited by Barbara Funnell © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC CHANOTPTE RFOR OUTLI SALENE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 9.1 Introduction 9.7 Partition Involves Separation of the 9.2 Bacterial Replication Is Connected to the Chromosomes Cell Cycle 9.8 Chromosomal Segregation Might Require Site-Specific Recombination © Jones &9.3 Bartlett The Shape Learning, and Spatial LLC Organization © Jones & Bartlett Learning, LLC of a Bacterium Are Important During 9.9 The Eukaryotic Growth Factor Signal NOT FOR SALEChromosome OR DISTRIBUTION Segregation and Cell Division NOT FORTransduction SALE OR DISTRIBUTION Pathway Promotes Entry 9.4 Mutations in Division or Segregation Affect to S Phase Cell Shape 9.10 Checkpoint Control for Entry into S Phase: 9.5 FtsZ Is Necessary for Septum Formation p53, a Guardian of the Checkpoint © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 9.6 min and noc/slm Genes Regulate the 9.11 Checkpoint Control for Entry into S Phase: Location of theNOT Septum FOR SALE OR DISTRIBUTIONRb, a Guardian of theNOT Checkpoint FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC • Replication© Jones requires & Bartlett coordination Learning, of these replicons LLC 9.1 Introduction to reproduce DNA during a discrete period of the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION A major difference between prokaryotes and eukaryotes is the cell cycle. way in which replication is controlled and linked to the cell cycle. • The decision about whether to replicate is determined In eukaryotes, the following are true: by a complex pathway that regulates the cell cycle. • Duplicated chromosomes are segregated to daugh- • Chromosomes reside in the nucleus. ter cells during mitosis by means of a special © Jones & Bartlett• Each Learning,chromosome consistsLLC of many units of repli-© Jones & Bartlett Learning, LLC apparatus. NOT FOR SALEcation OR calledDISTRIBUTION replicons. NOT FOR SALE OR DISTRIBUTION 228 Top texture: © Laguna Design / Science Source; Chapter Opener: © Laguna Design/Science Source. 9781284104646_CH09_227_244.indd 228 01/02/17 5:09 PM © Jones & Bartlett Learning LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION. Mother A unit cell has a circular chromosome © Jones & Bartlett Learning, LLC S © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONG1 NOT FORReplication SALE ORinitiates DISTRIBUTION when cell passes critical size Divide Mitosis G2 M Replication generates Daughter Daughter catenated daughter © Jones & BartlettStart Learning, LLC chromosomes © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Daughter chromosomes Grow Interphase = G1 + S + G2 are separated © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION SeptumNOT divides FOR cell SALE OR DISTRIBUTION FIGURE 9.1 A growing cell alternates between cell division of a mother cell into two daughter cells and growth back to the original size. Daughter cells separate © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC FIGURE 9.2 Replication initiates at the bacterial origin when a NOT FOR SALEIn eukaryotic OR DISTRIBUTION cells, replication of DNA is confined to theNOT cellFOR passes SALE a critical OR threshold DISTRIBUTION of size. Completion of replication second part of the cell cycle called S phase, which follows G1 produces daughter chromosomes that might be linked by phase (see FIGURE 9.1). The eukaryotic cell cycle is composed recombination or that might be catenated. They are separated and moved to opposite sides of the septum before the bacterium of alternating rounds of growth followed by DNA replication is divided into two. and then cell division. After the cell divides into two daugh- ter cells, each has the option© Jones to continue & Bartlett dividing or Learning, stop and LLC © Jones & Bartlett Learning, LLC enter G0. If the decisionNOT is to continue FOR SALEto divide, OR the cellDISTRIBUTION must NOT FOR SALE OR DISTRIBUTION grow back to the size of the original parent cell before divi- would trigger initiation. This is consistent with the fact that sion can occur again. protein synthesis is needed for the initiation event. Another The G1 phase of the cell cycle is concerned primarily possibility is that an inhibitor protein might be synthesized with growth (although G1 is an abbreviation for first gap or activated at a fixed point and then diluted below an effec- because© Jonesthe early &cytologists Bartlett could Learning, not see any LLC activity). In tive level by© theJones increase & Bartlettin cell volume. Learning, Current LLCmodels G1 everythingNOT FOR except SALE DNA beginsOR DISTRIBUTION to be doubled: RNA, pro- suggest thatNOT variations FOR of SALE both possibilities OR DISTRIBUTION operate to turn tein, lipids, and carbohydrates. The progression from G1 into initiation on and then off precisely in each cell cycle. Syn- S is very tightly regulated and is controlled by a checkpoint. thesis of active DnaA protein, the bacterial initiator protein, For a cell to be allowed to progress into S phase, there must reaches a threshold that turns on initiation, and the activity be a certain minimum amount of growth that is biochemi- of inhibitors turns subsequent initiations off for the rest of © Jones &cally Bartlett monitored. Learning, In addition, LLC there must not be any damage© Jonesthe cell & cycle. Bartlett This is Learning, described in the LLC The Replicon: Initiation NOT FORto SALE the DNA. OR Damaged DISTRIBUTION DNA or too little growth prevents theNOT ofFOR Replication SALE chapter OR .DISTRIBUTION cell from progressing into S phase. When S phase is com- Bacterial chromosomes are specifically compacted and plete, G2 phase commences; there is no control point and no arranged inside the cell, and this organization is important sharp demarcation. for proper segregation, or partition, of daughter chromo- The start of S phase is signaled by the activation of the somes at cell division. Some of the events in partitioning the first replicon—usually ©in Joneseuchromatin—in & Bartlett areas Learning,of active LLCdaughter chromosomes are consequences© Jones & of Bartlett the circularity Learning, LLC genes. Over the next fewNOT hours, FOR initiation SALE events OR occurDISTRIBUTION at of the bacterial chromosome.NOT Circular FOR chromosomes SALE OR are DISTRIBUTION other replicons in an ordered manner. said to be catenated when one passes through another, con- However, replication in bacteria, as shown in FIGURE 9.2, necting them. Catenation is a consequence of incomplete is triggered at a single origin when the cell mass increases removal of topological links during DNA replication, and past a threshold level, and the segregation of the daughter topoisomerases are required to remove these links and sep- chromosomes© Jones is &accomplished Bartlett Learning,by ensuring thatLLC they find arate the chromosomes.©