Chapter 12 The Cell Cycle PowerPoint Lectures for Biology Eighth Edition Neil Campbell and Jane Reece Overview The Key Roles of Cell Division 100 m a Reproduction An amoeba a single celled eukaryote is dividing into two cells Each new cell will be an individual organism LM 200 m 20 m b Growth and development c Tissue renewal These dividing This micrograph shows a bone marrow cells arrow will sand dollar embryo shortly give rise to new blood cells LM after the fertilized egg divided forming two cells LM Cellular Organization of the Genetic Material The DNA molecules in a cell Are packaged into chromosomes Figure 12 3 50 m 0 5 m A eukaryotic cell has multiple chromosomes one of which is represented here Before duplication each chromosome has a single DNA molecule Once duplicated a chromosome consists of two sister chromatids connected at the centromere Each chromatid 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 Chromosome duplication including DNA synthesis Centromere Separation of sister chromatids Centromeres Sister chromatids Sister chromatids The cell cycle consists of The mitotic phase Interphase INTERPHASE S DNA synthesis C M yto ito ki si ne s si s G1 MI M TOT P IC HA SE Figure 12 5 G2 Mitosis consists of five distinct phases G2 OF INTERPHASE Centrosomes with centriole pairs Nucleolus Chromatin duplicated Nuclear envelope Plasma membrane PROMETAPHASE PROPHASE Early mitotic spindle Aster Chromosome consisting of two sister chromatids Centromere Fragments of nuclear envelope Kinetochore Nonkinetochore microtubules Kinetochore microtubule Mitosis consists of five distinct phases METAPHASE ANAPHASE Metaphase plate Spindle Centrosome at one spindle pole TELOPHASE AND CYTOKINESIS Cleavage furrow Daughter chromosomes Nuclear envelope forming Nucleolus forming Microtubules and Kinetochores Aster Sister chromatids Centrosome Metaphase Plate Kinetochores Overlapping nonkinetochore microtubules Kinetochores microtubules Microtubules 0 5 m Centrosome 1 m Chromosomes Microtubules and Kinetochores 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 Kinetochore Spindle pole Figure 12 8 Cytokinesis A Closer Look In animal cells cytokinesis occurs by a process known as cleavage forming a cleavage furrow Cleavage furrow Contractile ring of microfilaments 100 m Daughter cells a Cleavage of an animal cell SEM In plant cells during cytokinesis a cell plate forms Vesicles forming cell plate Wall of patent cell 1 m Cell plate New cell wall Daughter cells b Cell plate formation in a plant cell SEM Mitosis in a plant cell Chromatine Nucleus Nucleolus condensing Chromosome Metaphase The Anaphase The 2 Prometaphase 3 5 1 Prophase spindle is complete 4 chromatids of each The chromatin We now see discrete and the chromosomes chromosome have is condensing chromosomes each attached to microtubules separated and the The nucleolus is consists of two at their kinetochores beginning to identical sister daughter chromosomes are all at the metaphase are moving to the ends disappear chromatids Later plate Although not in prometaphase the of cell as their yet visible nuclear envelop will kinetochore in the micrograph fragment microtubles shorten the mitotic spindle is staring to from Figure 12 10 Telophase Daughter nuclei are forming Meanwhile cytokinesis has started The cell plate which will divided the cytoplasm in two is growing toward the perimeter of the parent cell Binary Fission Origin of replication Cell wall Plasma Membrane E coli cell 1 Chromosome replication begins Soon thereafter one copy of the origin moves rapidly toward the other end of the cell 2 Replication continues One copy of the origin is now at each end of the cell 3 Replication finishes The plasma membrane grows inward and new cell wall is deposited 4 Two daughter cells result Figure 12 11 Two copies of origin Origin Bacterial Chromosome Origin The Evolution of Mitosis A hypothetical sequence for the evolution of mitosis a 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 b 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 c 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 within the nucleus Microtubules separate the chromosomes and the nucleus splits into two daughter nuclei d Most 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 Figure 12 12 A D Bacterial chromosome Chromosomes Microtubules Intact nuclear envelope Kinetochore microtubules Intact nuclear envelope Kinetochore microtubules Centrosome Fragments of nuclear envelope Evidence for Cytoplasmic Signals Molecules present in the cytoplasm Regulate progress through the cell cycle EXPERIMENTS In each experiment cultured mammalian cells at two different phases of the cell cycle were induced to fuse Experiment 2 Experiment 1 S G1 M S M G1 RESULTS S When a cell in the S phase was fused with a cell in G1 the G1 cell immediately entered the S phase DNA was synthesized M 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 CONCLUSION The results of fusing cells at two different phases of the cell cycle suggest that molecules present in the Figure 12 13 A B cytoplasm of cells in the S or M phase control the progression of phases The Cell Cycle Control System The sequential events of the cell cycle Are directed by a distinct cell cycle control system which is
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