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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bacterial cell Bacterial chromosome: Double-stranded DNA Origin of replication Septum 1 2 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromosome Rosettes of Chromatin Loops Scaffold protein Chromatin Loop Solenoid Scaffold protein Chromatin loop DNA Double Helix (duplex) Nucleosome Histone core DNA 4 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Homologous chromosomes Homologous chromosomes Kinetochore Replication Cohesin proteins Centromere Kinetochores Sister chromatids Sister chromatids 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. M Phase Metaphase Anaphase Prometaphase Telophase Prophase G2 G1 S Interphase G2 Mitosis M Phase Cytokinesis S G1 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cohesin proteins Chromatid Centromere region of chromosome Kinetochore Kinetochore microtubules Metaphase chromosome 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. INTERPHASE G2 CYTOKINESIS MITOSIS Prophase Centrioles (replicated; animal cells only) Prometaphase Metaphase 80 µm 80 µm Chromatin (replicated) Mitotic spindle beginning to form Condensed chromosomes Chromosomes aligned on metaphase plate 80 µm Centromere and Mitotic kinetochore spindle Anaphase 80 µm Kinetochore microtubule Telophase 80 µm 80 µm 80 µm Polar microtubule Chromosomes Nucleus reforming Kinetochore microtubule Aster Cleavage furrow Nuclear membrane Nucleolus Nucleus • 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 Kinetochore microtubule Polar microtubule • 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) Polar microtubule • 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 © Andrew S. Bajer, University of Oregon 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 57 µm Polar microtubule Centrioles Kinetochore microtubule Aster Metaphase plate Sister chromatids © Andrew S. Bajer, University of Oregon 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metaphase Pole Overlapping microtubules Pole Late Anaphase Pole Overlapping Pole microtubules © Dr. Jeremy Pickett-Heaps 2 µm 11 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0.7 µm Vesicles containing Nucleus membrane components fusing to form cell plate Cell wall © B.A. Palevits & E.H. Newcomb/BPS/Tom Stack & Associates 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prokaryotes 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. Chromosome Some Protists 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. FtsZ protein Microtubule Chromosome Other Protists A spindle of microtubules 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 chromosomes to each pole. Yeasts 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. Kinetochore microtubule Animals 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. Spindle pole body Kinetochore microtubule Fragments of nuclear envelope Kinetochore microtubule Central spindle of microtubules Septum Polar microtubule Nucleus Centrioles Kinetochore Centriole Polar microtubule 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. High Concentration MPF activity Cyclin Low G2 M G1 S G2 M G1 S G2 M 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G2/M checkpoint Spindle checkpoint M G2 S G1/S checkpoint (Start or restriction point) G1 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cyclin-dependent kinase (Cdk) P Cyclin P 17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G2/M Checkpoint Spindle Checkpoint Cdc2/Mitotic Cyclin APC • Replication completed • DNA integrity • Chromosomes attached at metaphase plate M G2 G1/S Checkpoint Cdk1/Cyclin B S • Growth factors • Nutritional state of cell • Size of cell G1 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G2/M Checkpoint Spindle Checkpoint Cdk1/Cyclin B APC • Replication completed • DNA integrity • Chromosomes attached at metaphase plate M G2 G1/S Checkpoint Cdc2/G1Cyclin S • Growth factors • Nutritional state of cell • Size of cell G1 19 Normal p53 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA repair enzyme 1. DNA damage is caused by heat, radiation, or chemicals. Abnormal p53 p53 allows cells with repaired DNA to divide. p53 protein Abnormal p53 protein 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. Cancer cell 2. The p53 protein fails to stop cell 3. Damaged cells continue to divide. division and repair DNA. Cell divides If other damage accumulates, the without repair to damaged DNA. cell can turn cancerous. 20