Chapter 12Overview: The Key Roles of Cell DivisionCellular Organization of the Genetic MaterialSlide 4Slide 5Mitosis consists of five distinct phasesSlide 7Microtubules and KinetochoresSlide 9Cytokinesis: A Closer LookSlide 11Mitosis in a plant cellBinary FissionThe Evolution of MitosisEvidence for Cytoplasmic SignalsThe Cell Cycle Control SystemSlide 17Slide 18Cell Cycle Control: External FactorsSlide 20Loss of Cell Cycle Controls in Cancer CellsSlide 22You should now be able to:Slide 24PowerPoint Lectures for Biology, Eighth EditionNeil Campbell and Jane ReeceChapter 12Chapter 12The Cell CycleOverview: The Key Roles of Cell Division100 µm(a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM).20 µm200 µm(b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM).(c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).•The DNA molecules in a cell–Are packaged into chromosomes50 µmFigure 12.3Cellular Organization of the Genetic Material0.5 µmChromosomeduplication(including DNA synthesis)CentromereSeparation of sister chromatidsSisterchromatidsCentromeresSister chromatidsA eukaryotic cell has multiplechromosomes, one of which is represented here. Before duplication, each chromosomehas a single DNA molecule.Once duplicated, a chromosomeconsists of two sister chromatidsconnected at the centromere. Eachchromatid contains a copy of the DNA molecule.Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells.Figure 12.4•The cell cycle consists of–The mitotic phase–InterphaseINTERPHASEG1S(DNA synthesis)G2CytokinesisMitosisMITOTIC(M) PHASEFigure 12.5Mitosis consists of five distinct phasesG2 OF INTERPHASEPROPHASEPROMETAPHASECentrosomes(with centriole pairs)Chromatin(duplicated)Early mitoticspindleAsterCentromereFragmentsof nuclearenvelopeKinetochoreNucleolusNuclearenvelopePlasmamembraneChromosome, consistingof two sister chromatidsKinetochore microtubule NonkinetochoremicrotubulesCentrosome at one spindle poleDaughter chromosomesMETAPHASE ANAPHASE TELOPHASE AND CYTOKINESISSpindleMetaphaseplateNucleolusformingCleavagefurrowNuclear envelopeformingMitosis consists of five distinct phasesMicrotubules and KinetochoresCentrosomeAsterSisterchromatidsMetaphasePlateKinetochoresOverlappingnonkinetochoremicrotubulesKinetochores microtubulesCentrosomeChromosomesMicrotubules0.5 µm1 µm•In anaphase, sister chromatids separate–And move along the kinetochore microtubules toward opposite ends of the cell EXPERIMENT 1 The microtubules of a cell in early anaphase were labeled with a fluorescent dye that glows in the microscope (yellow).SpindlepoleKinetochoreFigure 12.8Microtubules and KinetochoresCytokinesis: A Closer Look•In animal cells cytokinesis occurs by a process known as cleavage, forming a cleavage furrowCleavage furrowContractile ring of microfilamentsDaughter cells100 µm(a) Cleavage of an animal cell (SEM)•In plant cells, during cytokinesis a cell plate formsDaughter cells1 µmVesiclesforming cell plateWall of patent cellCell plateNew cell wall(b) Cell plate formation in a plant cell (SEM)1Prophase. The chromatinis condensing. The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is staring to from.Prometaphase.We now see discretechromosomes; each consists of two identical sister chromatids. Laterin prometaphase, the nuclear envelop will fragment.Metaphase. The spindle is complete,and the chromosomes,attached to microtubulesat their kinetochores, are all at the metaphase plate.Anaphase. Thechromatids of each chromosome have separated, and the daughter chromosomesare moving to the ends of cell as their kinetochoremicrotubles shorten.Telophase. Daughternuclei are forming. Meanwhile, cytokinesishas started: The cellplate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell.2 345NucleusNucleolusChromosomeChromatinecondensingFigure 12.10Mitosis in a plant cellBinary FissionOrigin ofreplicationE. coli cellBacterialChromosomeCell wallPlasma MembraneTwo copiesof originOriginOriginChromosome replication begins.Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell.1Replication continues. One copy ofthe origin is now at each end of the cell.2Replication finishes. The plasma membrane grows inward, andnew cell wall is deposited.3Two daughter cells result.4Figure 12.11The Evolution of Mitosis•A hypothetical sequence for the evolution of mitosisMost eukaryotes. In most other eukaryotes, including plants and animals, the spindle forms outside the nucleus, and the nuclear envelope breaks down during mitosis. Microtubules separate the chromosomes, and the nuclear envelope then re-forms.Dinoflagellates. In unicellular protists called dinoflagellates, the nuclear envelope remains intact during cell division, and the chromosomes attach to the nuclear envelope. Microtubules pass through the nucleus inside cytoplasmic tunnels, reinforcing the spatial orientation of the nucleus, which then divides in a fission process reminiscent of bacterial division.Diatoms. In another group of unicellular protists, the diatoms, the nuclear envelope also remains intact during cell division. But in these organisms, the microtubules form a spindle with in the nucleus. Microtubules separate the chromosomes, and the nucleus splits into two daughter nuclei.Prokaryotes. During binary fission, the origins of the daughter chromosomes move to opposite ends of the cell. The mechanism is not fully understood, but proteins may anchor the daughter chromosomes to specific sites on the plasma membrane.(a)(b)(c)(d)BacterialchromosomeMicrotubulesIntact nuclear envelopeChromosomesKinetochore microtubulesIntact nuclearenvelopeKinetochore microtubulesFragments ofnuclear envelopeCentrosomeFigure 12.12 A-DEvidence for Cytoplasmic Signals•Molecules present in the cytoplasm–Regulate progress through the cell cycleIn each experiment, cultured mammalian cells at two different phases of the cell cycle were induced to fuse.When a cell in the M phase was fused with a cell in G1, the G1 cell immediately began mitosis— a spindle formed and chromatin condensed, even though the chromosome had not been duplicated.
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