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UCSD BILD 1 - The Cell Cycle

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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsPowerPoint Lectures forBiology, Seventh EditionNeil Campbell and Jane ReeceLectures by Chris RomeroChapter 12The Cell CycleCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsOverview: The Key Roles of Cell Division• The ability of organisms to reproduce bestdistinguishes living things from nonliving matter• The continuity of life is based upon thereproduction of cells, or cell divisionCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• In unicellular organisms, division of one cellreproduces the entire organism• Multicellular organisms depend on cell division for:– Development from a fertilized cell– Growth– Repair• Cell division is an integral part of the cell cycle, thelife of a cell from formation to its own divisionLE 12-2Reproduction100 µmTissue renewalGrowth and development20 µm200 µmCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsConcept 12.1: Cell division results in geneticallyidentical daughter cells• Cells duplicate their genetic material before theydivide, ensuring that each daughter cell receivesan exact copy of the genetic material, DNA• A dividing cell duplicates its DNA, allocates thetwo copies to opposite ends of the cell, and onlythen splits into daughter cellsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsCellular Organization of the Genetic Material• A cell’s endowment of DNA (its geneticinformation) is called its genome• DNA molecules in a cell are packaged intochromosomesCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Every eukaryotic species has a characteristicnumber of chromosomes in each cell nucleus• Somatic (nonreproductive) cells have two sets ofchromosomes• Gametes (reproductive cells: sperm and eggs)have half as many chromosomes as somatic cells• Eukaryotic chromosomes consist of chromatin, acomplex of DNA and protein that condensesduring cell divisionLE 12-325 µmCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsDistribution of Chromosomes During Cell Division• In preparation for cell division, DNA is replicatedand the chromosomes condense• Each duplicated chromosome has two sisterchromatids, which separate during cell division• The centromere is the narrow “waist” of theduplicated chromosome, where the twochromatids are most closely attachedLE 12-4Chromosomeduplication(including DNAsynthesis)0.5 µmCentromereSisterchromatidsSeparationof sisterchromatidsCentromeres Sister chromatidsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Eukaryotic cell division consists of:– Mitosis, the division of the nucleus– Cytokinesis, the division of the cytoplasm• Gametes are produced by a variation of celldivision called meiosis• Meiosis yields nonidentical daughter cells thathave only one set of chromosomes, half as manyas the parent cellCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsConcept 12.2: The mitotic phase alternates withinterphase in the cell cycle• In 1882, the German anatomist Walther Flemmingdeveloped dyes to observe chromosomes duringmitosis and cytokinesis• To Flemming, it appeared that the cell simply grewlarger between one cell division and the next• Now we know that many critical events occurduring this stage in a cell’s lifeCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsPhases of the Cell Cycle• The cell cycle consists of– Mitotic (M) phase (mitosis and cytokinesis)– Interphase (cell growth and copying ofchromosomes in preparation for cell division)• Interphase (about 90% of the cell cycle) can bedivided into subphases:– G1 phase (“first gap”)– S phase (“synthesis”)– G2 phase (“second gap”)LE 12-5G1G2S(DNA synthesis)INTERPHASECytokinesis MITOTIC(M) PHASEMitosisCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Mitosis is conventionally divided into five phases:– Prophase– Prometaphase– Metaphase– Anaphase– Telophase• Cytokinesis is well underway by late telophase[Animations and videos listed on slide following figure]LE 12-6caG2 OF INTERPHASEPROPHASE PROMETAPHASELE 12-6daMETAPHASE ANAPHASETELOPHASE AND CYTOKINESIS10 µmCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsVideo: Animal MitosisVideo: Animal MitosisVideo: Sea Urchin (time lapse)Video: Sea Urchin (time lapse)Animation: Mitosis OverviewAnimation: Mitosis OverviewCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe Mitotic Spindle: A Closer Look• The mitotic spindle is an apparatus ofmicrotubules that controls chromosome movementduring mitosis• Assembly of spindle microtubules begins in thecentrosome, the microtubule organizing center• The centrosome replicates, forming twocentrosomes that migrate to opposite ends of thecell, as spindle microtubules grow out from them• An aster (a radial array of short microtubules)extends from each centrosomeCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• The spindle includes the centrosomes, the spindlemicrotubules, and the asters• Some spindle microtubules attach to thekinetochores of chromosomes and move thechromosomes to the metaphase plateLE 12-7MicrotubulesChromosomesSisterchromatidsAsterCentrosomeMetaphaseplateKineto-choresKinetochoremicrotubules0.5 µmOverlappingnonkinetochoremicrotubules1 µmCentrosomeCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• In anaphase, sister chromatids separate and movealong the kinetochore microtubules towardopposite ends of the cell• The microtubules shorten by depolymerizing attheir kinetochore endsLE 12-8bChromosomemovementMicrotubuleMotorproteinChromosomeKinetochoreTubulinsubunitsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Nonkinetochore microtubules from opposite polesoverlap and push against each other, elongatingthe cell• In telophase, genetically identical daughter nucleiform at opposite ends of the cellCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings• Taxol is an anticancer drug extracted from the Pacific yewtree. In animal cells, taxol disrupts microtubule formation bybinding to microtubules and accelerating their assembly fromthe


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UCSD BILD 1 - The Cell Cycle

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