Bacterial cell. Origin of replication. Septum

Transcription

1 Bacterial cell Bacterial chromosome: Double-stranded DNA Origin of replication Septum 1 2

2 3 Chromosome Rosettes of Chromatin Loops Scaffold protein Chromatin Loop Solenoid Scaffold protein Chromatin loop DNA Double Helix (duplex) Nucleosome Histone core DNA 4

3 5 Homologous chromosomes Homologous chromosomes Replication Centromere Cohesin proteins s Sister chromatids Sister chromatids 6

4 M Phase Prometaphase Prophase Metaphase Anaphase Telophase G 2 G 1 S Interphase G 2 Mitosis M Phase Cytokinesis S G 1 7 Cohesin proteins Chromatid Centromere region of chromosome microtubules Metaphase chromosome 8

5 INTERPHASE G 2 MITOSIS Prophase Prometaphase Metaphase Anaphase Telophase CYTOKINESIS Centrioles (replicated; animal cells only) Chromatin (replicated) 80 µm Mitotic spindle beginning to form 80 µm Condensed chromosomes 80 µm Centromere and Mitotic kinetochore spindle Chromosomes aligned on metaphase plate 80 µm Chromosomes Nucleus reforming microtubule 80 µm 80 µm Polar microtubule microtubule 80 µm Aster Nuclear Nucleolus membrane Nucleus Chromosomes condense and become visible Chromosomes appear as two DN A has been replicated sister chromatids held together Centrioles replicate (animal cells) at the centromere Cell prepares for division 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 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 microtubule 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 Cleavage furrow 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 Polar microtubule Centrioles 57 µm microtubule Metaphase plate Sister chromatids Aster Andrew S. Bajer, University of Oregon 10

6 Metaphase Pole Overlapping microtubules Pole Late Anaphase Pole Overlapping Pole microtubules Dr. Jeremy Pickett-Heaps 2 µm 11 12

7 0.7 µm Nucleus Vesicles containing membrane components fusing to form cell plate Cell wall B.A. Palevits & E.H. Newcomb/BPS/Tom Stack & Associates 13 Prokaryotes Some Protists Other Protists Yeasts Animals 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 FtsZ protein 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 microtubules forms between two pairs of centrioles at opposite ends of the cell. The spindle passes through one tunnel in the intact nuclear envelope. microtubules form between kinetochores on the chromosomes and the spindle poles and pull the chromosomes 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. microtubule Spindle pole body Spindle microtubules begin to form between centrioles outside of nucleus. Centrioles move to the poles and the nuclear envelope breaks down. microtubules attach kinetochores of chromosomes to spindle poles. Polar microtubules extend toward the center of the cell and overlap. Microtubule Chromosome microtubule Central spindle of microtubules microtubule Fragments of nuclear envelope Septum Polar microtubule Nucleus Centrioles Centriole Polar microtubule 14

8 High Concentration MPF activity Cyclin Low G 2 M G 1 S G 2 M G 1 S G 2 M 15 G 2 /M checkpoint Spindle checkpoint M G 2 S G 1 /S checkpoint (Start or restriction point) G 1 16

9 Cyclin-dependent kinase (Cdk) P Cyclin P 17 G 2 /M Checkpoint Cdc2/Mitotic Cyclin Replication completed DNA integrity Spindle Checkpoint APC Chromosomes attached at metaphase plate M G 2 G 1 /S Checkpoint Cdk1/Cyclin B S Growth factors Nutritional state of cell Size of cell G 1 18

10 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 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