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In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization.

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Presentation on theme: "In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization."— Presentation transcript:

1 In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization Cell Cycle and Mitosis 8.1 to 8.11

2 Genetic information is stored and transmitted through DNA All the DNA in a cell constitutes the cell’s genome A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes

3 Fig. 12-3 20 µm

4 Genetic Information is stored and transmitted through DNA Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Somatic cells (nonreproductive cells) have two sets of chromosomes - DIPLOID Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells - HAPLOID Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division

5 Fig. 12-4 0.5 µmChromosomes Chromosome duplication (including DNA synthesis) Chromo- some arm Centromere Sister chromatids DNA molecules Separation of sister chromatids Centromere Sister chromatids

6 The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell

7 Interphase Majority of the cell cycle Time when a cell’s metabolic activity is very high and the cell performs various functions 3 stages ◦G1 – cell growth ◦S – DNA replication (Synthesis of DNA) ◦G2 – prepare for mitosis

8 M Phase (mitotic phase) About 10% of the cell cycle 2 stages ◦Mitosis – nuclear division ◦Cytokinesis – cytoplasm division Results in two genetically identical cells

9 The cell cycle is directed by internal controls or checkpoints.

10 Cell Cycle Checkpoints For many cells, the G 1 checkpoint seems to be the most important one If a cell receives a go-ahead signal at the G 1 checkpoint, it will usually complete the S, G 2, and M phases and divide If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G 0 phase

11 Cell Cycle Checkpoints Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin- dependent kinases (Cdks) The activity of cyclins and Cdks fluctuates during the cell cycle MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G 2 checkpoint into the M phase

12 Fig. 12-17 M G1G1 S G2G2 M G1G1 SG2G2 M G1G1 MPF activity Cyclin concentration Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle Degraded cyclin Cdk G1G1 S G2G2 M G2G2 checkpoint Cyclin is degraded Cyclin MPF (b) Molecular mechanisms that help regulate the cell cycle Cyclin accumulation

13 Internal and External signals provide stop-and-go signs at the checkpoints An example of an internal signal is that kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture

14 Fig. 12-18 Petri plate Scalpels Cultured fibroblasts Without PDGF cells fail to divide With PDGF cells prolifer- ate 10 µm

15 Fig. 12-19 Anchorage dependence Density-dependent inhibition (a) Normal mammalian cells (b) Cancer cells 25 µm

16 Mitosis passes a complete genome from the parent cell to the daughter cell Mitosis is conventionally divided into five phases: ◦Prophase ◦Prometaphase ◦Metaphase ◦Anaphase ◦Telophase Cytokinesis is well underway by late telophase

17 Fig. 12-6b PrometaphaseProphase G 2 of Interphase Nonkinetochore microtubules Fragments of nuclear envelope Aster Centromere Early mitotic spindle Chromatin (duplicated) Centrosomes (with centriole pairs) Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule

18 Fig. 12-7 Microtubules Chromosomes Sister chromatids Aster Metaphase plate Centrosome Kineto- chores Kinetochore microtubules Overlapping nonkinetochore microtubules Centrosome 1 µm 0.5 µm

19 Fig. 12-6d MetaphaseAnaphase Telophase and Cytokinesis Cleavage furrow Nucleolus forming Metaphase plate Centrosome at one spindle pole Spindle Daughter chromosomes Nuclear envelope forming

20 Fig. 12-8b Kinetochore Microtubule Tubulin Subunits Chromosome movement Motor protein

21 Fig. 12-9 Cleavage furrow 100 µm Contractile ring of microfilaments Daughter cells (a) Cleavage of an animal cell (SEM)(b) Cell plate formation in a plant cell (TEM) Vesicles forming cell plate Wall of parent cell Cell plate Daughter cells New cell wall 1 µm

22 Summary of Mitosis What must occur before mitosis? ◦DNA replication ◦Pass G2 checkpoint What is “checked” at the ‘M’ checkpoint? ◦Chromosome attachment to microtubule What follows mitosis? ◦Cytokinesis What are the products of the mitosis? ◦2 genetically identical cells Why do we need mitosis? ◦Growth, repair, asexual reproduction


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