7-1 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Chapter 7: Cell division

7-2 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Cell cycle Period of time from origin of cell to division of cell into daughter cells Types of division –mitosis produces daughter cells with genetic complement identical to parent cell  somatic cells –meiosis produces daughter cells with half the genetic complement of parent cell  reproductive cells

7-3 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Cell division in prokaryotes Binary fission –division into two daughter cells, each with one copy of the genetic material Single, circular DNA molecule attached to plasma membrane –replicates –new molecule attached to separate point of plasma membrane –membrane between two molecules lengthens –plasma membrane and cell wall grow inward –cell divides

7-4 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Cell cycle in eukaryotes Cell division in eukaryotes involves two processes: –nuclear division  division of nuclear DNA –cytokinesis  physical division of cell

7-5 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Cell cycle Synthesis of DNA and other molecules during interphase –G 1 (first gap) phase –S (synthesis) phase –G 2 (second gap) phase Chromosomes become visible and divide during M phase (mitosis)

7-6 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 7.3a: Cell cycle in actively growing cells

7-7 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Interphase G 1 phase –gap between mitosis and synthesis S phase –replication of DNA generates sister chromatids G 2 phase –gap between synthesis and mitosis

7-8 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Mitosis in animal cells Chromosomes condense Nuclear membrane breaks down Chromosomes attach to mitotic spindle (microtubules) Identical copies of chromosomes migrate to opposite poles of mitotic spindle Nuclear membrane reforms around chromosomes

7-9 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Stages of mitosis End of G 2 phase of interphase leads into mitosis Prophase –chromatin in nucleus condenses into chromosomes –chromosomes composed of identical sister chromatids joined by centromeres –centrosome at each end produces microtubules that form asters (radial arrays) in the spindle (cont.)

7-10 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 7.6 (a) + (b): Cell dividing (interphase, prophase)

7-11 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Stages of mitosis (cont.) Prometaphase –asters enclose nuclear envelope –nuclear envelope disaggregates –kinetochore fibres (microtubules) bind to kinetochores in chromosomes Metaphase –chromosomes line up along middle of spindle in metaphase plate (cont.)

7-12 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 7.6 (c) + (d): Cell dividing (prometaphase, metaphase)

7-13 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Stages of mitosis (cont.) Anaphase –sister chromatids separate to form chromosomes –chromosomes migrate to opposite poles (anaphase A) –poles move apart, microtubules slide over one another, elongating spindle (anaphase B) –mechanism of migration remains unclear Telophase –chromosomes decondense –new nuclear envelope forms, surrounding each group of chromosomes

7-14 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 7.6 (e) + (f): Cell dividing (anaphase, telophase)

7-15 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Cytokinesis in animal cells Cytokinesis occurs in late mitosis –starts during anaphase B –completed in telophase Actin filaments form contractile ring that pulls plasma membrane and constricts cell –results in cleavage of cell to produce daughter cells

7-16 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 7.6 (g) + (h): Cytokinesis

7-17 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Mitosis in plants Plant cells differ from animal cells Lack centrosomes and astral spindles –microtubules form barrel-shaped spindle Enclosed in rigid walls –during anaphase, fibres thicken between chromosomes –phragmoplast forms –inside phragmoplast, membrane vesicles form new cytoplasmic membrane and cell plate (new wall) –preprophase band close to cell wall marks site where growing cell plate will fuse with existing cell wall

7-18 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Control of cell cycle progression Progression regulated by cyclins and cyclin- dependent (Cdks) kinases S-phase-promoting factor (SPF) –phosphorylates and activates proteins required for DNA replication M-phase-promoting factor (MPF) –phosphorylates and activates proteins that induce chromosome condensation (histones) and nuclear envelope breakdown (nuclear envelope scaffold proteins) –remains active until chromosomes are aligned at metaphase (cont.)

7-19 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Control of cell cycle progression (cont.) Protease degrades cyclin component of MPF –proteins dephosphorylated –chromosomes decondense –nuclear envelope reforms

7-20 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Checkpoint control Mechanisms to determine integrity of processes during cell division Detect defects in DNA integrity or in attachment of chromosomes to mitotic spindle Detected errors result in inhibition of SPF or MPF activity, blocking progression and interrupting cell cycle

7-21 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Meiosis Reduction division producing haploid reproductive cells (gametes) During meiosis –DNA replication → cell division (meiosis I) → cell division (meiosis II)

7-22 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Fig. 7.13: Meiosis in animal cell

7-23 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Meiosis I Prophase I –homologous chromosomes pair up (synapsis) –chromatids of homologous chromosomes may cross over, exchanging portions of genetic material –crossing over occurs at chiasmata –generates novel combinations of genetic material Metaphase I –homologous chromosomes aligned on central plane of spindle –kinetochores on each chromosome in a homologous pair attach to opposite poles (cont.)

7-24 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Meiosis I (cont.) Anaphase I –homologous chromosomes move to opposite poles –sister chromatids do not separate At end of meiosis I, each daughter cell contains one set of chromosomes

7-25 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Meiosis II Resembles mitosis Anaphase II –sister chromatids separate to form chromosomes –chromosomes migrate to opposite poles –results in four haploid cells (cont.)

7-26 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Meiosis II (cont.) Males –two rounds of division results in four haploid sperm Females –two rounds of division not accompanied by cytokinesis –one cell with haploid nucleus –remaining nuclei form polar bodies that degenerate or are expelled Gamete formation in some groups may involve a subsequent mitotic division

7-27 Copyright  2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint Genetic consequence of meiosis Generates genetic diversity in sexually reproducing organisms through recombination –crossing over during prophase of meiosis I –mixing of maternal and paternal genomes in zygote