1 The Cell Cycle and How Cells Divide 2 Review: Vocabulary - Chromosomes Chromosome: spool to hold DNA in the nucleus Homologous: pairs of chromosomes that code for the same traits Autosome: all chromosomes except X & Y Sex Chromosomes: determine sex of organisms X & Y 3 Review: Vocabulary - Cells Gametes: sex cells (egg/ovum and sperm) Diploid ( di = 2) having pairs of chromosomes (all cells except gametes) Haploid (1/2) cells having only one of each type of chromosome. Somatic Cells: all non-sex cells Zygote: the union of an ovum & sperm 4 Review: What is DNA? The recipe for YOU! (genetic info) Packaged into chromosomes 50 m Figure 12.3 5 Review: Chromosomes Human cells have 46 chromosomes. 23 nearly-identical pairs (homologous) 6 Review: Karyotype An ordered, visual representation of chromosomes from a single organism. 7 The Math: Chromosome = (n) n = the number of chromosomes in the haploid cell Egg (n) + sperm (n) = zygote (2n) n + n = 2n Maternal set of chromosomes (n = 3) Paternal set of chromosomes (n = 3) 2n = 6 Two sister chromatids of one replicated chromosome Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set) Centromere 8 Math Practice egg = 23 n= _____ 2n = ____ sperm = 4 n= ______ 2n = ____ ovum = 12 n = _____ 2n = ____ sperm = ___ n = 5 2n = ____ ovum = ____ n = ____ 2n = 20 9 Homologues Homologous chromosomes: Look the same Control the same traits May code for different forms of each trait each one was inherited from a different parent 10 Review: Chromosome Duplication 0.5 m 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. In preparing for cell division, DNA is replicated and the chromosomes condense Each duplicated chromosome has two sister chromatids, attached at the centromere 11 Cell Cycle Life Cycle of a cell Interphase normal cell activity Mitotic phase cell divsion INTERPHASE Growth G 1 (DNA synthesis) Growth G 2 Cell Divsion 12 Phases of the Cell Cycle Interphase G 1 - primary growth S DNA repilcation G 2 - secondary growth M - mitosis C - cytokinesis 13 3 Purposes for Cell Division 20 m 100 m 200 m Reproduction. Growth and development. Tissue renewal or replacement 14 Cell Division Mitosis (mi-to-sis) My two sis(ter cells) 15 Mitosis: produces identical cells The cell division process that forms two new nuclei (cells); each of which has the same number of chromosomes. 16 Prophase prepare chromosomes condense Each duplicated chromosome appears as two identical sister chromatids joined together. The mitotic spindle begins to form. PROPHASE Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids 17 Metaphase: meet in middle the longest stage of mitosis, about 20 min. The centrosomes are at opposite ends of the cell. The chromosomes meet in the middle of the cell METAPHASE Spindle Metaphase plate Centrosome at one spindle pole 18 Anaphase apart shortest stage of mitosis, lasting only a few minutes. each chromosome pair pulls apart. Each chromatid becomes a full- fledged chromosome. By the end of anaphase, the two ends of the cell have equal and complete sets of chromosomes. ANAPHASE Daughter chromosomes 19 Telophase tuck in Two daughter nuclei begin to form in the cell. The chromosomes become less condensed. Mitosis, is now complete. TELOPHASE AND CYTOKINESIS Nucleolus forming Cleavage furrow Nuclear envelope forming 20 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 21 METAPHASEANAPHASETELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes Mitotic Division of an Animal Cell 22 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 Nucleus Nucleolus Chromosome Chromatine condensing 23 Cytokinesis In Animal And Plant Cells Daughter cells Cleavage furrow Contractile ring of microfilaments Daughter cells 100 m 1 m 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) 24 25 Cell Cycle and Mitosis 3-D VideooyPkoyPk