Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bacterial cell Septum Bacterial chromosome: Double-stranded DNA Origin of replication 1

2

3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ChromosomeRosettes of Chromatin LoopsChromatin LoopSolenoid Nucleosome Histone core Chromatin loop Scaffold protein Scaffold protein DNA DNA Double Helix (duplex) 4

5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Homologous chromosomes Sister chromatids Centromere Replication Kinetochore Kinetochores Cohesin proteins Centromere 6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G1G1 G2G2 S Interphase Mitosis M Phase Cytokinesis M Phase G2G2 S G1G1 Metaphase Prophase Anaphase Telophase Prometaphase 7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromatid Kinetochore Cohesin proteins Centromere region of chromosome Metaphase chromosome Kinetochore microtubules 8

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. INTERPHASE G 2 ProphasePrometaphaseMetaphaseAnaphaseTelophase Nucleus Nucleolus Aster Chromosomes Polar microtubule Nucleus reforming Cleavage furrow 80 µm CYTOKINESIS MITOSIS Centrioles (replicated; animal cells only) Nuclear membrane DN A has been replicated Centrioles replicate (animal cells) Cell prepares for division Chromosomes condense and become visible Chromosomes appear as two sister chromatids held together at the centromere Cytoskeleton is disassembled: spindle begins to form Golgi and ER are dispersed Nuclear envelope breaks down Chromosomes attach to microtubules at the kinetochores Each chromosome is oriented such that the kinetochores of sister chromatids are attached to microtubules from opposite poles. Chromosomes move to equator of the cell All chromosomes are aligned at equator of the cell, called the metaphase plate Chromosomes are attached to opposite poles and are under tension Proteins holding centromeres of sister chromatids are degraded, freeing individual chromosomes Chromosomes are pulled to opposite poles (anaphase A) Spindle poles move apart (anaphase B) Chromosomes are clustered at opposite poles and decondense Nuclear envelopes re-form around chromosomes Golgi complex and ER re-form In animal cells, cleavage furrow forms to divide the cells In plant cells, cell plate forms to divide the cells Polar microtubule Kinetochore microtubule Chromatin (replicated) 80 µm Mitotic spindle beginning to form Condensed chromosomes Centromere and kinetochore Mitotic spindle Chromosomes aligned on metaphase plate Kinetochore microtubule Polar microtubule Kinetochore microtubule © Andrew S. Bajer, University of Oregon 9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Centrioles Sister chromatids Aster 57 µm Kinetochore microtubule Metaphase plate Polar microtubule © Andrew S. Bajer, University of Oregon 10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metaphase Pole 2 µm Overlapping microtubules Late Anaphase Overlapping microtubules © Dr. Jeremy Pickett-Heaps 11

12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell wall Nucleus 0.7 µm Vesicles containing membrane components fusing to form cell plate © B.A. Palevits & E.H. Newcomb/BPS/Tom Stack & Associates 13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Septum FtsZ protein Chromosome Microtubule Nucleus Kinetochore microtubule CentriolesKinetochore Polar microtubule Spindle pole body Kinetochore microtubule Centriole ProkaryotesSome ProtistsOther ProtistsAnimals Kinetochore microtubule Polar microtubule No nucleus, usually have single circular chromosome. After DNA is replicated, it is partitioned in the cell. After cell elongation, FtsZ protein assembles into a ring and facilitates septation and cell division. Nucleus present and nuclear envelope remains intact during cell division. Chromosomes line up. Microtubule fibers pass through tunnels in the nuclear membrane and set up an axis for separation of replicated chromosomes, and cell division. A spindle of micro- tubules forms between two pairs of centrioles at opposite ends of the cell. The spindle passes through one tunnel in the intact nuclear envelope. Kinetochore microtubules form between kinetochores on the chromosomes and the spindle poles and pull the chromo- somes to each pole. Nuclear envelope remains intact; spindle microtubules form inside the nucleus between spindle pole bodies. A single kinetochore microtubule attaches to each chromosome and pulls each to a pole. Spindle microtubules begin to form between centrioles outside of nucleus. Centrioles move to the poles and the nuclear envelope breaks down. Kinetochore microtubules attach kinetochores of chromosomes to spindle poles. Polar microtubules extend toward the center of the cell and overlap. Yeasts Central spindle of microtubules Fragments of nuclear envelope 14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G1G1 SG2G2 MG2G2 MG1G1 SG2G2 M Concentration Low High MPF activity Cyclin 15

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G2G2 M S G1G1 Spindle checkpointG 2 /M checkpoint G 1 /S checkpoint (Start or restriction point) 16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cyclin P Cyclin-dependent kinase (Cdk) P 17

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Growth factors Size of cell G2G2 M S G1G1 Spindle Checkpoint APCCdc2/Mitotic Cyclin Chromosomes attached at metaphase plate Replication completed DNA integrity G 2 /M Checkpoint G 1 /S Checkpoint Cdk1/Cyclin B Nutritional state of cell 18

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Growth factors Size of cell G2G2 M S G1G1 Spindle Checkpoint APCCdk1/Cyclin B Chromosomes attached at metaphase plate Replication completed DNA integrity G 2 /M Checkpoint G 1 /S Checkpoint Cdc2/G 1 Cyclin Nutritional state of cell 19

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. DNA damage is caused by heat, radiation, or chemicals. 2. Cell division stops, and p53 triggers enzymes to repair damaged region. 3. p53 triggers the destruction of cells damaged beyond repair. p53 allows cells with repaired DNA to divide. 1. DNA damage is caused by heat, radiation, or chemicals. 2. The p53 protein fails to stop cell division and repair DNA. Cell divides without repair to damaged DNA. 3. Damaged cells continue to divide. If other damage accumulates, the cell can turn cancerous. DNA repair enzyme Cancer cell p53 protein Normal p53 Abnormal p53 Abnormal p53 protein 20