Cell Division

Paired “threads” Figure 8.1 An Early View of Mitosis

Chapter 8 A dividing animal cell

Cell Theory and Cell Division Cell Theory n Def: All organisms consist of cells and arise from pre-existing cells n Cell cycle: predictable sequence of cell life events Chromosomes: thread-like bodies visible during cell division

Cell Theory and Cell Division n Events of the Cell Cycle Interphase: non-dividing part of the cycle Mitosis: nuclear division part of the cycle Two cells produced each with the same number of chromosomes as the parent cell Cytokinesis: cytoplasmic (cell) division part of the cycle

DIVISION M Mitosis G2G2 Second gap G1G1 DNA synthesis First gap S Figure 8.5 INTERPHASE The Cell Cycle

Parent cell Replicated chromosomes condense at the start of mitosis Mitosis During mitosis, sister chromatids separate and two daughter cells are formed. Parent cell and daughter cell contain the same complement of chromosomes. Figure 8.7 Cell Duplication

Cell Theory and Cell Division Interphase Events n Gap 1 phase: normal growth of cell Organelles replicated Additional cytoplasm accumulated, growth in size ~ 7-9 hours long

Cell Theory and Cell Division n S phase: synthesis of new DNA (chromosomes) Each chromosome serves as a template and makes a copy of itself Duration: 6-8 hours

Chromosome Number of chromosomes: 4 Unreplicated chromosomes Figure 8.6a

Replicated chromosomes Chromosome Sister chromatids Centromere Number of chromosomes: 4 Figure 8.6b

Cell Theory and Cell Division n Gap 2 phase: a period of time between S and beginning of mitosis Synthesis of materials used in mitosis Microtubule proteins, ATP, other organelles 4-5 hours duration n Duration times based upon one organism, others may differ

DIVISION M Mitosis G2G2 Second gap G1G1 DNA synthesis First gap S Figure 8.5 INTERPHASE The Cell Cycle

Cell Theory and Cell Division Set of chromosomes n Ploidy: a term referring to the numbers of sets of chromosomes in a given cell n Def: one of each kind of chromosome that is characteristic of a species Human set has 23 chromosomes n Haploid (n): one set n Diploid (2n): two sets

Figure 8.2 Mitosis in Progress

Mitosis (M Phase) Prophase Events n Chromosomes condense, become visible Replicated chromosomes (=chromatids) joined at the centromere n Spindle apparatus forms and attaches to kinetochore (structure associated with the centromere) n Nuclear membrane begins to disintegrate

PRIOR TO MITOSIS MITOSIS Chromosomes replicate, forming sibling chromatids Sibling chromatids separate Centrosomes Centrioles Early mitotic spindle Kinetochore 1. Chromosomes replicate in parent cell. 2. Prophase: Chromosomes condense and mitotic spindle begins to form. Nuclear envelope breaks down. 3. Metaphase: Chromosomes migrate to middle of cell Figure 8.8, left Interphase ProphaseMetaphase Stages of Mitosis

Mitosis (M Phase) Metaphase Events n Chromosomes align along the equator of the cell n Spindle appratus anchored (in animals) at the centriole (site of spindle formation)

PRIOR TO MITOSIS MITOSIS Chromosomes replicate, forming sibling chromatids Sibling chromatids separate Centrosomes Centrioles Early mitotic spindle Kinetochore 1. Chromosomes replicate in parent cell. 2. Prophase: Chromosomes condense and mitotic spindle begins to form. Nuclear envelope breaks down. 3. Metaphase: Chromosomes migrate to middle of cell Figure 8.8, left Interphase ProphaseMetaphase Stages of Mitosis

Mitosis (M Phase) Anaphase Events n Centromere divides allowing spindle apparatus to shorten and separate sibling chromatids n Separated chromatids called chromosomes n Chromosomes move to opposite poles of the cell

4. Anaphase: Sister chromatids separate. Chromosomes are pulled to opposite poles of the cell. 5. Telophase: The nuclear envelope reforms. 6. Cytokinesis: The cell divides. Figure 8.8, right Anaphase Telophase Stages of Mitosis

Mitosis (M Phase) Telophase and Cytokinesis Events n Nuclear envelope begins to form around chromosomes n Chromosomes become diffuse n Spindle apparatus disappears n Cytokinesis begins

4. Anaphase: Sister chromatids separate. Chromosomes are pulled to opposite poles of the cell. 5. Telophase: The nuclear envelope reforms. 6. Cytokinesis: The cell divides. Figure 8.8, right Anaphase Telophase Stages of Mitosis

Mitosis (M Phase) n Cytokinesis in animals characterized by a cleavage furrow n Cytokinesis in plants characterized by the formation of a new wall between newly forming nuclei

Cytokinesis in animal cells Figure 8.9a

Cytokinesis in plant cells Figure 8.9b Note: new cell wall forming between new nuclei

Figure 8.2 Mitosis in Progress

Interphase 17  m Figure 8.10a Animal Cell Mitosis

Prophase Figure 8.10b 17  m Animal Cell Mitosis

Metaphase Figure 8.10c 17  m Animal Cell Mitosis

Anaphase Figure 8.10d 17  m Animal Cell Mitosis

Telophase Figure 8.10e 17  m Animal Cell Mitosis

Cytokinesis Figure 8.10f 17  m Animal Cell Mitosis

M phase cells (mitotic cells) induce interphase cells to begin M phase. Mitotic cell G 1 phase cell S phase cell G 2 phase cell Mitotic cell Fuse cells Figure 8.12a Chromosomes from G 1 phase cell condense Chromosomes from S phase cell condense Chromosomes from G 2 phase cell condense Evidence of Cell Cycle Control

S phase cells induce only G 1 cells to begin S phase. S phase cellG 1 phase cellG 2 phase cell S phase cell Fuse cells and add radioactive thymidine ( * ) Fuse cells and add radioactive thymidine G 1 phase chromosomes are labeled; they have entered S phase G 2 phase chromosomes are labeled; they do not enter S phase Figure 8.12b Evidence of Cell Cycle Control

M phase cytoplasm induces oocyte to begin M phase. Inject cytoplasm from M phase cell Inject cytoplasm from interphase cell Early mitotic spindle Oocyte is driven into M phase Oocyte remains in G 2 phase Figure 8.13b

Control of the Cell Cycle Mitosis Promotion Factor (MPF) n Def: molecular complex that induces mitosis in all eukaryotes n Composition: two polypeptide subunits Protein kinase (enzyme that phosphorylates proteins) Cyclin: protein that acts with protein kinase

Control of the Cell Cycle Cyclin n Def: protein that binds with protein kinase and together promote mitosis n Activity MPF activity fluctuates with the concentration of cyclin Cyclin concentration and MPF activity increase to M-phase and then decreases

Cyclin concentrations regulate MPF activity. M phase MPF activity Cyclin concentration Time Figure 8.15a Control of the Cell Cycle

GROWTH FACTORS ARE INVOLVED IN PASSING THE G 1 CHECKPOINT Cyclin CdK ATP ADP Target protein PiPi 1. Arrival of growth factors from other cells. 2. Growth factors cause increase in cyclin concentration. 3. Cyclin activates cyclin-dependent kinase. 4. Kinases activate S phase proteins, leading to cell division. Figure 8.18a Example: Control of Cell Cycle

HOW ARE S PHASE PROTEINS ACTIVATED? Rb Cyclin CdK Rb E2F Rb ATP ADP PiPi PiPi E2F S Phase proteins mRNA DNA 1. In normal cells, Rb protein binds to E2F and shuts down the cell cycle. 2. If growth factors arrive and activate the cyclin-CdK complex, Rb becomes phosphorylated. 3. E2F is released 4. E2F stimulates the production of S phase proteins. Figure 8.18b Example: Control of Cell Cycle

Control of the Cell Cycle Roll of Genes n Genes encode cell cycle proteins n Mutant genes  mutant cell cycle control proteins  unregulated growth  tumor formation (cancer) n Ultimately cancerous cells invade other organs.

Figure 8.17 CANCER SPREADS Tumors in liver spread from other tissues