100 µm 200 µm 20 µm (a) Reproduction (b) Growth and (c) Tissue renewal development 1 20 µm 2 0.5 µm Chromosomes DNA molecules Chromo- Chromosome some arm duplication (including DNA synthesis) Centromere Sister chromatids Separation of sister chromatids Centromere Sister chromatids 3 G S 1 (DNA synthesis) G2 4 G2 of Interphase Prophase Prometaphase Metaphase Anaphase Telophase and Cytokinesis Centrosomes Chromatin Early mitotic Aster Centromere Fragments Nonkinetochore Metaphase Cleavage Nucleolus (with centriole (duplicated) spindle of nuclear microtubules plate furrow forming pairs) envelope Daughter Nuclear Nucleolus Nuclear Plasma Chromosome, consisting Kinetochore Kinetochore Spindle Centrosome at chromosomes one spindle pole envelope envelope membrane of two sister chromatids microtubule forming 5 Aster Centrosome Sister chromatids Microtubules Chromosomes Metaphase plate Kineto- chores Centrosome 1 µm Overlapping nonkinetochore Kinetochore microtubules microtubules 0.5 µm 6 EXPERIMENT Kinetochore Spindle pole Mark RESULTS CONCLUSION Chromosome movement Kinetochore Motor Tubulin Microtubule protein subunits Chromosome 7 Vesicles Wall of 1 µm 100 µm forming parent cell Cleavage furrow cell plate Cell plate New cell wall Contractile ring of Daughter cells microfilaments Daughter cells (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM) 8 Nucleus Chromatin 10 µm Nucleolus condensing Chromosomes Cell plate 1 Prophase 2 Prometaphase 3 Metaphase 4 Anaphase 5 Telophase 9 Cell wall Origin of replication Plasma membrane E. coli cell Bacterial Two copies chromosome of origin Origin Origin 10 Bacterial chromosome (a) Bacteria Chromosomes Microtubules Intact nuclear envelope (b) Dinoflagellates Kinetochore microtubule Intact nuclear envelope (c) Diatoms and yeasts Kinetochore microtubule Fragments of nuclear envelope (d) Most eukaryotes 11 EXPERIMENT Experiment 1 Experiment 2 S G1 M G1 RESULTS S S M M When a cell in the When a cell in the S phase was fused M phase was fused with with a cell in G1, the G1 a cell in G1, the G1 nucleus immediately nucleus immediately entered the S began mitosis—a phase—DNA was spindle formed and synthesized. chromatin condensed, even though the chromosome had not been duplicated. 12 G1 checkpoint Control system S G1 M G2 M checkpoint G2 checkpoint 13 G0 G1 checkpoint G1 G1 (a) Cell receives a go-ahead (b) Cell does not receive a signal go-ahead signal 14 M G1 S G2 M G1 S G2 M G1 MPF activity Cyclin concentration Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle Cyclin accumulation Cyclin Cdk Degraded cyclin G2 Cdk Cyclin is checkpoint degraded Cyclin MPF (b) Molecular mechanisms that help regulate the cell cycle 15 Scalpels Petri plate Without PDGF With PDGF cells fail to divide cells prolifer- ate Cultured fibroblasts 10 µm 16 Anchorage dependence Density-dependent inhibition Density-dependent inhibition 25 µm 25 µm (a) Normal mammalian cells (b) Cancer cells 17 Lymph vessel Tumor Blood vessel Cancer Glandular cell tissue Metastatic tumor 1 A tumor grows 2 Cancer cells 3 Cancer cells spread 4 Cancer cells may from a single invade neigh- to other parts of survive and cancer cell. boring tissue. the body. establish a new tumor in another part of the body. 18 .