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Chapter 12 The Cell Cycle.

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Presentation on theme: "Chapter 12 The Cell Cycle."— Presentation transcript:

1 Chapter 12 The Cell Cycle

2 Multicellular organisms depend on cell division for:
Continuity of Life is Based on Cell Division In unicellular organisms, division of one cell reproduces the entire organism. Multicellular organisms depend on cell division for: Development from a fertilized cell Growth Repair Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3 Functions of Cell Division
Fig. 12-2 Functions of Cell Division 100 µm 200 µm 20 µm (a) Reproduction (b) Growth and development (c) Tissue renewal Repair Figure 12.2 The functions of cell division

4 Concept 12.1: Mitotic Cell Division results in genetically identical daughter cells
Most cell division is mitotic and results in daughter cells with identical genetic information, DNA. A special type of meiotic cell division produces nonidentical daughter cells (gametes, or sperm and egg cells). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

5 Cellular Organization of the Genetic Material
All the DNA in a cell constitutes the cell’s genome. A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

6 Fig. 12-3 Figure 12.3 Eukaryotic chromosomes 20 µm

7 Somatic cells (2n) (body cells) have two sets (pairs) of chromosomes.
Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus. Somatic cells (2n) (body cells) have two sets (pairs) of chromosomes. Gametes (n) (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells. Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

8 Distribution of Chromosomes During Eukaryotic Cell Division
In preparation for cell division, DNA is replicated and the chromosomes condense. Each duplicated chromosome has two identical sister chromatids, which separate during cell division. The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9 0.5 µm Chromosomes DNA molecules Chromo- some arm Chromosome
Fig. 12-4 0.5 µm Chromosomes DNA molecules Chromo- some arm Chromosome duplication (including DNA synthesis) Centromere Sister chromatids Figure 12.4 Chromosome duplication and distribution during cell division Separation of sister chromatids Centromere Sister chromatids

10 Eukaryotic cell division consists of:
Mitosis, the division of the nucleus Cytokinesis, the division of the cytoplasm Gametes (n) are produced by a variation of cell division called meiosis = reduction division. Meiosis yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cell. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

11 Phases of the Cell Cycle
The cell cycle consists of Mitotic (M) phase (mitosis and cytokinesis) Interphase: G1 normal cell growth S copying of chromosomes G2 growth in preparation for cell division. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

12 S (DNA synthesis) G1 Cytokinesis G2 Mitosis
Fig. 12-5 INTERPHASE S (DNA synthesis) G1 Cytokinesis G2 Mitosis Figure 12.5 The cell cycle MITOTIC (M) PHASE

13 Mitosis is conventionally divided into five phases:
Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis is well underway by late telophase. For the Cell Biology Video Myosin and Cytokinesis, go to Animation and Video Files. BioFlix: Mitosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

14 Chromosome, consisting of two sister chromatids
Fig. 12-6 G2 of Interphase Prophase Prometaphase Metaphase Anaphase Telophase and Cytokinesis Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Nonkinetochore microtubules Metaphase plate Cleavage furrow Nucleolus forming Figure 12.6 The mitotic division of an animal cell Daughter chromosomes Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore Kinetochore microtubule Spindle Centrosome at one spindle pole Nuclear envelope forming

15 Chromosome, consisting of two sister chromatids
Fig. 12-6b G2 of Interphase Prophase Prometaphase Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Nonkinetochore microtubules Figure 12.6 The mitotic division of an animal cell Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore Kinetochore microtubule

16 Telophase and Cytokinesis
Fig. 12-6d Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Nucleolus forming Figure 12.6 The mitotic division of an animal cell Daughter chromosomes Nuclear envelope forming Spindle Centrosome at one spindle pole

17 The Mitotic Spindle: A Closer Look
The mitotic spindle is an apparatus of microtubules that controls chromosome movement during mitosis. During prophase, assembly of spindle microtubules begins in the centrosome, the MTOC microtubule organizing center. The centrosome replicates, forming two centrosomes that migrate to opposite ends of the cell, as spindle microtubules grow out from them. An aster (a radial array of short microtubules) extends from each centrosome. For the Cell Biology Video Spindle Formation During Mitosis, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

18 During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes. At metaphase, the chromosomes are all lined up at the metaphase plate, the midway point between the spindle’s two poles. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

19 Centrosome Fig. 12-7 Aster Sister chromatids Microtubules Chromosomes
Metaphase plate Kinetochores Centrosome 1 µm Figure 12.7 The mitotic spindle at metaphase Overlapping nonkinetochore microtubules Kinetochore microtubules 0.5 µm

20 The microtubules shorten by depolymerizing at their kinetochore ends.
In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell The microtubules shorten by depolymerizing at their kinetochore ends. For the Cell Biology Video Microtubules in Anaphase, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

21 EXPERIMENT RESULTS CONCLUSION Kinetochore Spindle pole Mark Chromosome
Fig. 12-8 EXPERIMENT Kinetochore Spindle pole Mark RESULTS Figure 12.8 At which end do kinetochore microtubules shorten during anaphase? CONCLUSION Chromosome movement Kinetochore Motor protein Tubulin subunits Microtubule Chromosome

22 EXPERIMENT Kinetochore Spindle pole Mark RESULTS Fig. 12-8a
Figure 12.8 At which end do kinetochore microtubules shorten during anaphase? RESULTS

23 Chromosome movement Kinetochore Tubulin Motor Subunits Microtubule
Fig. 12-8b CONCLUSION Chromosome movement Kinetochore Tubulin Subunits Motor protein Microtubule Figure 12.8 At which end do kinetochore microtubules shorten during anaphase? Chromosome

24 Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cell. In telophase, genetically identical daughter nuclei form at opposite ends of the cell. For the Cell Biology Video Microtubules in Cell Division, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

25 Cytokinesis: A Closer Look
In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow in the plasma membrane. In plant cells, a cell plate forms from Golgi vesicles (membrane) during cytokinesis. Animation: Cytokinesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

26 Fig. 12-9 Cytokinesis Vesicles forming cell plate Wall of parent cell 1 µm 100 µm Cleavage furrow Cell plate New cell wall Figure 12.9 Cytokinesis in animal and plant cells Contractile ring of microfilaments Daughter cells Daughter cells (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)

27 10 µm Fig. 12-10 Plant Cell Mitotic Division Nucleus Chromatin
condensing 10 µm Nucleolus Chromosomes Cell plate Figure Mitosis in a plant cell 1 Prophase 2 Prometaphase 3 Metaphase 4 Anaphase 5 Telophase

28 Binary Fission Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission. In binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes move apart as the cell elongates. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

29 Binary Fission Cell wall Origin of replication Plasma membrane
E. coli cell Bacterial chromosome Two copies of origin Origin Origin Figure Bacterial cell division by binary fission

30 The Evolution of Mitosis
Since prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fission. Certain protists exhibit types of cell division that seem intermediate between binary fission and mitosis. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

31 (b) Protists: Dinoflagellates = algae
Fig Bacterial chromosome (a) Bacteria Chromosomes Microtubules Intact nuclear envelope (b) Protists: Dinoflagellates = algae Kinetochore microtubule Intact nuclear envelope Figure A hypothetical sequence for the evolution of mitosis (c) Diatoms and yeasts Kinetochore microtubule Fragments of nuclear envelope (d) Most eukaryotes

32 Bacterial chromosome (a) Bacteria Chromosomes Microtubules
Fig ab Bacterial chromosome (a) Bacteria Chromosomes Microtubules Figure A hypothetical sequence for the evolution of mitosis Intact nuclear envelope (b) Dinoflagellates

33 Kinetochore microtubule Intact nuclear envelope (c) Diatoms and yeasts
Fig cd Kinetochore microtubule Intact nuclear envelope (c) Diatoms and yeasts Kinetochore microtubule Figure A hypothetical sequence for the evolution of mitosis Fragments of nuclear envelope (d) Most eukaryotes

34 The frequency of cell division varies with the type of cell.
Concept 12.3: The eukaryotic cell cycle is regulated by a molecular control system The frequency of cell division varies with the type of cell. These cell cycle differences result from regulation at the molecular level. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

35 Evidence for Cytoplasmic Signals
The cell cycle appears to be driven by specific chemical signals present in the cytoplasm. Some evidence for this hypothesis comes from experiments in which cultured mammalian cells at different phases of the cell cycle were fused to form a single cell with two nuclei. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

36 EXPERIMENT RESULTS Experiment 1 Experiment 2 S G1 M G1 S S M M
Fig EXPERIMENT Experiment 1 Experiment 2 S G1 M G1 RESULTS S S M M When a cell in the S phase was fused with a cell in G1, the G1 nucleus immediately entered the S phase—DNA was synthesized. When a cell in the M phase was fused with a cell in G1, the G1 nucleus immediately began mitosis—a spindle formed and chromatin condensed, even though the chromosome had not been duplicated. Figure Do molecular signals in the cytoplasm regulate the cell cycle?

37 The Cell Cycle Control System
The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock. The cell cycle control system is regulated by both internal and external controls The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

38 G1 checkpoint Control system S G1 G2 M M checkpoint G2 checkpoint
Fig G1 checkpoint Control system S G1 G2 M Figure Mechanical analogy for the cell cycle control system M checkpoint G2 checkpoint

39 For many cells, the G1 checkpoint seems to be the most important one.
If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide. If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

40 G0 G1 G1 G1 checkpoint (b) Cell does not receive a
Fig G0 G1 checkpoint Figure The G1 checkpoint G1 G1 Cell receives a go-ahead G1 checkpoint. (b) Cell does not receive a go-ahead signal --> exit.

41 The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases
Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin-dependent kinases (Cdks). The activity of cyclins and Cdks fluctuates during the cell cycle. MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

42 M G1 S G2 M G1 S G2 M G1 Fig. 12-17 MPF activity Cyclin concentration
Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle G1 S Cdk Figure Molecular control of the cell cycle at the G2 checkpoint Cyclin accumulation M Degraded cyclin G2 G2 Cdk Cyclin is degraded checkpoint Cyclin MPF (b) Molecular mechanisms that help regulate the cell cycle

43 (a) Fluctuation of MPF activity and cyclin concentration during
Fig a M G1 S G2 M G1 S G2 M G1 MPF activity Cyclin concentration Figure Molecular control of the cell cycle at the G2 checkpoint Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle

44 (b) Molecular mechanisms that help regulate the cell cycle
Fig b G1 S Cdk Cyclin accumulation M Degraded cyclin G2 G2 checkpoint Cdk Figure Molecular control of the cell cycle at the G2 checkpoint Cyclin is degraded Cyclin MPF (b) Molecular mechanisms that help regulate the cell cycle

45 Stop and Go Signs: Internal and External Signals at the Checkpoints
An example of an internal signal is that kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase. Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide. For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

46 Scalpels Petri plate Without PDGF cells fail to divide With PDGF
Fig Scalpels Petri plate Without PDGF cells fail to divide Figure The effect of a growth factor on cell division With PDGF cells prolifer- ate Cultured fibroblasts 10 µm

47 External Signals Besides growth factors, another example of external signals is density-dependent inhibition, in which crowded cells stop dividing Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

48 Density-dependent inhibition
Fig Anchorage dependence Density-dependent inhibition Density-dependent inhibition Figure Density-dependent inhibition and anchorage dependence of cell division 25 µm 25 µm (a) Normal mammalian cells (b) Cancer cells

49 Loss of Cell Cycle Controls in Cancer Cells
Cancer cells do not respond normally to the body’s control mechanisms. Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence. Cancer cells may not need growth factors to grow and divide: They may make their own growth factor They may convey a growth factor’s signal without the presence of the growth factor They may have an abnormal cell cycle control system. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

50 A normal cell is converted to a cancerous cell by a process called transformation.
Cancer cells form tumors, masses of abnormal cells within otherwise normal tissue. If abnormal cells remain at the original site, the lump is called a benign tumor. Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

51 Cancer: Does NOT obey cell cycle control signals
Lymph vessel Tumor Blood vessel Cancer cell Glandular tissue Metastatic tumor 1 A tumor grows from a single cancer cell. 2 Cancer cells invade neigh- boring tissue. 3 Cancer cells spread to other parts of the body. 4 Cancer cells may survive and establish a new tumor in another part of the body. Figure The growth and metastasis of a malignant breast tumor

52 Review G1 S Cytokinesis Mitosis G2 MITOTIC (M) PHASE Prophase
INTERPHASE G1 S Cytokinesis Mitosis G2 MITOTIC (M) PHASE Prophase Telophase and Cytokinesis Prometaphase Anaphase Metaphase

53 Various Cell Cycle Phases in onion root tip:

54 Fig. 12-UN3

55 Fig. 12-UN4

56

57 You should now be able to:
Describe the structural organization of the prokaryotic genome and the eukaryotic genome. List the phases of the cell cycle; describe the sequence of events during each phase. List the phases of mitosis and describe the events characteristic of each phase. Draw or describe the mitotic spindle, including centrosomes, kinetochore microtubules, nonkinetochore microtubules, and asters. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

58 Compare cytokinesis in animals and plants.
Describe the process of binary fission in bacteria and explain how eukaryotic mitosis may have evolved from binary fission. Explain how the abnormal cell division of cancerous cells escapes normal cell cycle controls. Distinguish between benign, malignant, and metastatic tumors. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings


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