cell cycle and mitosis

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Figure 12.1 The continuity of life is based on the reproduction of cells – CELL DIVISION

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unicellular organisms - division of one cell reproduces a new entire organism multicellular organisms - depend on cell division for Development and growth of tissues/organism Repair and Replace old and damaged cells Gamete production for sexual reproduction © 2011 Pearson Education, Inc.

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Mitosis results in daughter cells with identical genetic information (DNA) Meiosis , a special type of division that produces gametes (sperm and egg)….daughter cells with unique genetic information © 2011 Pearson Education, Inc. Somatic cells (non-reproductive cells) that have paired sets of homologous chromosomes – result of mitosis Gametes reproductive cells that have half as many chromosomes as somatic cells – result of only meiosis

Wingdings:

DNA molecules are packaged into chromosomes A cell’s genome  all the DNA in a cell A genome can consist of …… a single, long DNA molecule (prokaryotic cells) or Multiple DNA molecules (eukaryotic cells)

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TEM DNA double helix Histones chromatin - a complex of DNA and proteins that condenses during cell division

Figure 12.1:

Centromere Sister chromatids DNA is replicated and the chromosomes condense sister chromatids - joined copies of original chromosome (separate during cell division) where chromatids are joined Chromosome (one molecule of DNA) Duplicated chromosomes Centromere (Sister chromatids)

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Figure 12.5-1 Chromosome DNA molecules 1

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Figure 12.5-2 Chromosome DNA molecules Centromere Chromosome duplication Sister chromatids 1 2

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Figure 12.5-3 Chromosome DNA molecules Centromere Chromosome duplication Sister chromatids Separation of sister chromatids into 2 chromosomes 1 2 3 Chromosomes

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Phases of the Cell Cycle The cell cycle consists of……. Interphase (cell growth and duplication of chromosomes in preparation for cell division) Mitotic (M) phase (mitosis and cytokinesis – nuclear and cellular division) © 2011 Pearson Education, Inc. Cell Cycle - the life of a cell from formation to its own division

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Interphase (about 90% of the cell cycle) divided into…… G 1 phase (“first gap”) – mainly “normal” cell functions S phase (“synthesis”) – DNA replication G 2 phase (“second gap”) – cytoplasm and organelle duplication The cell grows during all three phases but ……… chromosomes are duplicated only during the S phase © 2011 Pearson Education, Inc.

Figure 12.5-1:

INTERPHASE G 1 G 2 S (DNA synthesis) MITOTIC (M) PHASE Cytokinesis Mitosis mainly “normal” cell functions cytoplasm and organelle duplication nuclear and cellular division

Figure 12.5-2:

Mitosis is divided into five phases Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis overlaps with telophase of mitosis © 2011 Pearson Education, Inc. Eukaryotic cell division consists of Mitosis - division of the genetic material in nucleus Cytokinesis - division of the cytoplasm

Figure 12.5-3:

Figure 12.7a G 2 of Interphase Prophase Prometaphase Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Nonkinetochore microtubules Kinetochore Kinetochore microtubule Start Mitosis

Phases of the Cell Cycle:

Figure 12.7b Metaphase Metaphase plate Anaphase Telophase and Cytokinesis Spindle Centrosome at one spindle pole Daughter chromosomes Cleavage furrow Nucleolus forming Nuclear envelope forming

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The Mitotic Spindle: mitotic spindle - microtubules that control chromosome movement during mitosis (In animal cells) assembly of spindle microtubules begins in the centrosome The centrosome replicates during interphase forming two centrosomes (w/ centrioles) that migrate to opposite ends of the cell during prometaphase © 2011 Pearson Education, Inc.

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G 2 of Interphase Prophase Prometaphase Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Nonkinetochore microtubules Kinetochore Kinetochore microtubule aster (short microtubules) extends from each centrosome Spindle includes: centrosomes, spindle microtubules, and asters

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Figure 12.8 Sister chromatids Aster Centrosome Metaphase plate Kineto- chores Overlapping nonkinetochore microtubules Kinetochore microtubules Microtubules Chromosomes Centrosome spindle microtubules attach to the kinetochores of chromosomes (protein complexes at centromeres) in metaphase chromosomes are lined up at metaphase plate (midway point btwn poles) Non-kinetochore microtubules from opposite poles overlap and push against each other, elongating the cell

Figure 12.7a:

Chromosome movement Microtubule Motor protein Chromosome Kinetochore Tubulin subunits Spindle fiber microtubules shorten by depolymerizing at their kinetochore ends

Figure 12.7b:

Figure 12.9 Chromosome movement Microtubule Motor protein Chromosome Kinetochore Tubulin subunits Kinetochore Mark Spindle pole sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell (poles)

The Mitotic Spindle::

Mitotic - Telophase - genetically identical daughter nuclei form at opposite ends of the cell Cytokinesis – division of cytoplasm © 2011 Pearson Education, Inc. In animal cells - cytokinesis occurs by a process known as cleavage , forming a cleavage furrow In plant cells - cell plate forms during cytokinesis

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Figure 12.10a Cleavage of an animal cell Cleavage furrow Contractile ring of microfilaments Two new Daughter cells

Figure 12.8:

Figure 12.10b Cell plate formation in a plant cell Golgi Vesicles forming cell plate Wall of parent cell Cell plate New cell wall Two new Daughter cells

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Figure 12.7a G 2 of Interphase Prophase Prometaphase Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids Fragments of nuclear envelope Nonkinetochore microtubules Kinetochore Kinetochore microtubule Start Mitosis

Figure 12.9:

Figure 12.7b Metaphase Metaphase plate Anaphase Telophase and Cytokinesis Spindle Centrosome at one spindle pole Daughter chromosomes Cleavage furrow Nucleolus forming Nuclear envelope forming

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Binary Fission in Bacteria Prokaryotes (bacteria and archaea ) reproduce by a cell division called binary fission Bacteria have one chromosome and no nucleus © 2011 Pearson Education, Inc.

Figure 12.10a:

1 Origin of replication E. coli cell Two copies of origin Bacterial chromosome Chromosome replication begins. chromosome replicates - beginning at the origins of replication Binary Fission

Figure 12.10b:

1 Origin of replication E. coli cell Two copies of origin Bacterial chromosome Origin Origin Chromosome replication begins. Replication continues. 2 Binary Fission the two daughter chromosomes actively move apart

Figure 12.7a:

1 E. coli cell Chromosome replication begins. Replication continues. Replication finishes. Two daughter cells result. 2 3 4 Binary Fission plasma membrane pinches inward dividing the cell

Figure 12.7b:

The Evolution of Mitosis Since prokaryotes evolved before eukaryotes…….. mitosis likely evolved from binary fission Some protists exhibit types of cell division that seem intermediate between binary fission and mitosis © 2011 Pearson Education, Inc.

Binary Fission in Bacteria:

Figure 12.13 (a) Bacteria (b) Dinoflagellates (d) Most eukaryotes Intact nuclear envelope Chromosomes Microtubules Intact nuclear envelope Kinetochore microtubule Kinetochore microtubule Fragments of nuclear envelope Bacterial chromosome (c) Diatoms and some yeasts

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The frequency of cell division varies with the type of cell The differences are due to regulation at the molecular level The cell cycle appears to be driven by specific chemical signals present in the cytoplasm © 2011 Pearson Education, Inc.

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INTERPHASE G 1 G 2 S (DNA synthesis) MITOTIC (M) PHASE Cytokinesis Mitosis mainly “normal” cell functions cytoplasm and organelle duplication nuclear and cellular division

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© 2011 Pearson Education, Inc. The eukaryotic cell is regulated by a Cell Cycle Control System Events of the cell cycle are directed by a cell cycle control system - regulated by both internal and external controls

The Evolution of Mitosis:

G 1 checkpoint G 1 G 2 G 2 checkpoint M checkpoint M S Control system At specific checkpoints the cell cycle stops until a go-ahead signal is received

Figure 12.13:

G 1 checkpoint G 1 G 1 G 0 Cell receives go-ahead signal. Cell does not receive go-ahead signal. If the cell does not receive a go-ahead signal at G 1 , it will exit the cycle, switch to a non-dividing state called the G 0 phase If a cell does receive a go-ahead signal at the G 1 checkpoint, it will usually complete the S, G 2 , and M phases and divide

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Cdk Degraded cyclin Cyclin is degraded MPF G 2 checkpoint Cdk Cyclin M S G 1 G 2 Cyclin accumulation MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G 2 checkpoint into the M phase Two types of regulatory proteins involved in cell cycle control: cyclins and cyclin-dependent kinases (Cdks)

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MPF activity fluctuates with the cyclin concentration during the cell cycle MPF activity Cyclin concentration Time M M M S S G 1 G 2 G 1 G 2 G 1 Cdks activity fluctuates because it is controlled by cyclins (and cyclin concentrations fluctuate in the cell cycle)

The eukaryotic cell is regulated by a Cell Cycle Control System:

Stop and Go: Internal and External Signals at the Checkpoints internal signal - kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase external signals - growth factors  proteins released by cells that stimulate other cells to divide © 2011 Pearson Education, Inc.

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Figure 12.18 A sample of human connective tissue is cut up into small pieces. Enzymes digest the extracellular matrix, resulting in a suspension of free fibroblasts. Cells are transferred to culture vessels. PDGF is added to half the vessels. Without PDGF With PDGF 1 2 3 4 For example……. platelet-derived growth factor (PDGF) stimulates division of human fibroblast cells

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Figure 12.19 Anchorage dependence Density-dependent inhibition Normal cells Cancer cells density-dependent inhibition - crowded cells stop dividing Most animal cells also exhibit anchorage dependence = they must be attached to a substratum to divide Cancer cells – exhibit neither density-dependent inhibition nor anchorage dependence

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Loss of Cell Cycle Controls in Cancer Cells Cancer cells may ……. make their own growth factor convey a growth factor’s signal without the presence of the growth factor have an abnormal cell cycle control system © 2011 Pearson Education, Inc. Cancer cells that are not eliminated by the immune system, form tumors, masses of abnormal cells

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Glandular tissue Tumor Lymph vessel Blood vessel Cancer cell Metastatic 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. Cancer cells may survive and establish a new tumor in another part of the body. 4 3 2 1 Malignant tumors - invade surrounding tissues Metastasize - cancer cells spread to other parts of the body If abnormal cells remain at the original site - benign tumor

Stop and Go: Internal and External Signals at the Checkpoints:

Mitosis Cytokinesis MITOTIC (M) PHASE G 1 G 2 S Telophase and Cytokinesis Anaphase Metaphase Prometaphase Prophase I T R HA S E E P N understanding the cell cycle and cell cycle signaling have led to advances in cancer treatment

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