18 LE 12-10 Chromatin condensing Nucleus Chromosomes Cell plate 10 µm NucleolusProphase. Thechromatin is condensing.The nucleolus is beginning to disappear.Although not yet visible in the micrograph, the mitotic spindle is starting to form.Prometaphase. Wenow see discrete chromosomes; eachconsists of two identical sister chromatids. Laterin prometaphase, thenuclear envelope will fragment.Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all atthe metaphase plate.Anaphase. Thechromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of the cell as their kinetochore micro-tubules shorten.Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell.
19 Microscopic view of Mitosis in Onion root tips Microscopic view of Mitosis in Onion root tips. Can you identify the stages?
20 LE 12-11_3 Cell wall Origin of replication Plasma membrane E. coli cellBacterialchromosomeChromosome replication begins.Soon thereafter,one copy of the origin moves rapidly toward the other end of the cell.Two copiesof originOriginOriginReplication continues. One copy of the origin is now at each end of the cell.Replication finishes.The plasma membrane grows inward, andnew cell wall is deposited.Two daughtercells result.
22 LE 12-15G0G1 checkpointG1G1If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.
23 Relative concentration LE 12-16aMG1SG2MG1SG2MMPF activityCyclinRelative concentrationTimeFluctuation of MPF activity and cyclin concentrationduring the cell cycle
24 Molecular mechanisms that help regulate the cell cycle LE 12-16bG1CyclinSCdkDegradedcyclinMG2accumulationG2checkpointCdkCyclin isdegradedCyclinMPFMolecular mechanisms that help regulate the cell cycle
25 Chromosome movement Kinetochore Tubulin subunits Motor Microtubule LE 12-8bChromosomemovementKinetochoreTubulinsubunitsMotorproteinMicrotubuleChromosome
26 Cells anchor to dish surface and divide (anchorage dependence). LE 12-18aCells anchor to dish surface anddivide (anchorage dependence).When cells have formed a completesingle layer, they stop dividing(density-dependent inhibition).If some cells are scraped away, theremaining cells divide to fill the gap andthen stop (density-dependent inhibition).25 µmNormal mammalian cells
27 Cancer cells do not exhibit anchorage dependence LE 12-18bCancer cells do not exhibitanchorage dependenceor density-dependent inhibition.25 µmCancer cells
28 Malignant cancer cells from the breast (See the ABNORMAL “crab” shape of the cells.)