1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings INTERPHASE G1G1 S (DNA synthesis) G2G2 Cytokinesis Mitosis MITOTIC (M) PHASE Ch. 12 The Cell Cycle Interphase M phase – Mitosis – Cytokinesis

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 20 µm 100 µm 200 µm (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM). Reproduction – unicellular organisms – binary fission in bacteria Growth & development from fertilized egg Repair (& replacement) of damaged cells Cell Division - Purpose

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 12.4 Chromosome duplication and distribution during cell division 0.5 µm Chromosome duplication (including DNA synthesis) Centromere Separation of sister chromatids Sister chromatids Centrometers Sister chromatids A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule. Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells.

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 12.5 The cell cycle INTERPHASE G1G1 S (DNA synthesis) G2G2 Cytokinesis Mitosis MITOTIC (M) PHASE 5-6hrs.10-12hrs. 4-6hrs. 1hr. growth 90% of cell’s life

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings INTERPHASE G1G1 S (DNA synthesis) G2G2 Cytokinesis Mitosis MITOTIC (M) PHASE An organism’s genome: -Total genes in the cell of a species -Nuclear & extra-nuclear (mito & chloro) Human chromosome number: -46 – somatic cell (body cells) -2n -diploid -23 – gamete (sex cells – sperm & egg) -n-n -haploid Chromosomes: -Chromatin -DNA & proteins

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Interphase Centromsomes – with 2 centrioles Nucleus – with mass of chromatin Nucleolus in nucleus

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings INTERPHASE G1G1 S (DNA synthesis) G2G2 Cytokinesis Mitosis MITOTIC (M) PHASE Phases of Mitosis Prophase Prometaphase – chromosomes are in Pairs Metaphase – chromosomes in Middle Anaphase – chromosomes Apart Telophase – Two cells

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 12.6 Exploring The Mitotic Division of an Animal Cell G 2 OF INTERPHASEPROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Nonkinetochore microtubules

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings METAPHASEANAPHASETELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes Figure 12.6 Exploring The Mitotic Division of an Animal Cell

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytokinesis: division of the cytoplasm animal cells – Forms cleavage furrow plant cells – Forms a cell plate

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 12.9 Cytokinesis in animal and plant cells Daughter cells Cleavage furrow Contractile ring of microfilaments Daughter cells 100 µm 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (SEM)

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Control system G 2 checkpoint – cyclin dependent complex CDK complex (go ahead signal) M checkpoint G 1 checkpoint G1G1 S G2G2 M Molecular Control of Cell Cycle regulated at checkpoints kinases - cyclin-dependent kinase (CDK) cyclins -MPF -maturation promoting factor -Cyclin + CDK = MPF -(mitosis promoting factor)

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 12.15 The G 1 checkpoint G 1 checkpoint G1G1 G1G1 G0G0 (a) If a cell receives a go-ahead signal at the G 1 checkpoint, the cell continues on in the cell cycle. (b) If a cell does not receive a go-ahead signal at the G 1 checkpoint, the cell exits the cell cycle and goes into G 0, a nondividing state.

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 12.16 Molecular control of the cell cycle at the G 2 checkpoint Accumulated cyclin molecules combine with recycled Cdk mol- ecules, producing enough molecules of MPF to pass the G 2 checkpoint and initiate the events of mitosis. MPF promotes mitosis by phosphorylating various proteins. MPF‘s activity peaks during metaphase. (breaking down nuclear envelop, etc.) 3 During G 1, conditions in the cell favor degradation of cyclin, and the Cdk component of MPF is recycled. 5 During anaphase, the cyclin component of MPF is degraded, terminating the M phase. The cell enters the G 1 phase. 4 2 Synthesis of cyclin begins in late S phase and continues through G 2. Because cyclin is protected from degradation during this stage, it accumulates. 1 Cdk G 2 checkpoint Cyclin MPF Cyclin is degraded Degraded Cyclin G1G1 G2G2 S M G1G1 G1G1 S G2G2 G2G2 S M M MPF activity Cyclin Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle (b) Molecular mechanisms that help regulate the cell cycle Relative Concentration MPF – maturation promoting factor

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Control of Cell Cycle Cyclin accumulates - late S phase – Binds to/activating CDK Producing MPF MPF at G 2 initiates mitosis Anaphase - cyclin component of MPF degrades M phase terminates - cell -> G 1

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Kinetochore microtubules shorten at their kinetochore ends CONCLUSION This experiment demonstrated that during anaphase, kinetochore microtubules shorten at their kinetochore ends, not at their spindle pole ends. This is just one of the experiments supporting the hypothesis that during anaphase, a chromosome tracks along a microtubule as the microtubule depolymerizes at its kinetochore end, releasing tubulin subunits Chromosome movement Microtubule Motor protein Chromosome Kinetochore Tubulin subunits

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prophase: chromatin - condenses nucleoli disappear. sister chromatids appear mitotic spindle forms centrosomes move away from each other

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prometaphase: nuclear envelope fragments microtubules join chromosomes 2 chromatids/chromosome – kinetochore center “kinetochore microtubules.” - jerk the chromosomes back and forth. Nonkinetochore microtubules interact with opposite poles

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metaphase: Metaphase - longest stage – about 20 min. centrosomes at opposite ends. chromosomes convene on metaphase plate, – at centromeres Sister chromatid kinetochores – attached to kinetochore microtubules spindle - apparatus of microtubules

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anaphase: shortest stage - a few minutes. 2 sister chromatids part – chromatid becomes chromosome move toward opposite ends of the cell, – kinetochore microtubules shorten cell elongates – nonkinetochore microtubules lengthen finally the ends have equivalent—complete— collections of chromosomes

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Telophase: 2 daughter nuclei form Nuclear envelopes form chromosomes -less condensed Mitosis – the division of 1 nucleus into 2 genetically identical nuclei - complete

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 12.7 The mitotic spindle at metaphase Sister chromatids Metaphase Plate Kinetochores Overlapping nonkinetochore microtubules Kinetochores microtubules Centrosome Chromosomes Microtubules 0.5 µm Centrosome Aster 1 µm

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lack of Cell Cyle Controls - Cancer Cells 25 µm Cells anchor to dish surface and divide (anchorage dependence). When cells have formed a complete single layer, they stop dividing (density-dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the gap and then stop (density-dependent inhibition). Cancer cells do not exhibit anchorage dependence or density-dependent inhibition. 25 µm Cancer cells. Cancer cells usually continue to divide well beyond a single layer, forming a clump of overlapping cells. Normal mammalian cells. The availability of nutrients, growth factors, and a substratum for attachment limits cell density to a single layer. (a) (b) Figure 12.18 Density-dependent inhibition and anchorage dependence of cell division

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 12.19 The growth and metastasis of a malignant breast tumor A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Cancer cells spread through lymph and blood vessels to other parts of the body. A small percentage of cancer cells may survive and establish a new tumor in another part of the body. 2 43 1 Tumor Glandular tissue Cancer cell Blood vessel Lymph vessel Metastatic Tumor

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lab: Figure 12.10 Mitosis in a plant cell 1 Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is staring to from. Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelop will fragment. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of cell as their kinetochore microtubles shorten. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell. 23 4 5 Nucleus Nucleolus Chromosome Chromatine condensing

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plant Cells – meristematic tissue (root tip)

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bacterial cell division (binary fission) Origin of replication E. coli cell Bacterial Chromosome Cell wall Plasma Membrane Two copies of origin Origin Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. 1 Replication continues. One copy of the origin is now at each end of the cell. 2 Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. 3 Two daughter cells result. 4