Transcript Mitosis
Cell Division Part 1 A Generalized Cell Golgi body Nuclear envelope Nucleolus Chromosomal DNA Nucleus Polyribosomes Ribosome Rough ER Cytoplasm Membrane protein Plasma membrane Smooth ER Lysosome Microfilaments Centrioles Mitochondrion Microtubules (b) Animal cell The Cell Cycle DNA Synthesis Interphase S Synthesis G1 Gap 1 M Mitosis G2 Gap 2 Growth Gene expression Differentiation Two daughter cells Gene expression Quality control Actual division process Three Little Words Geneticist Need to Hear… Homolog, Loci, Allele Gene loci (location) Unreplicated chromosome pair Homologous pair of chromosomes Genotype: A b c A B c AA Bb cc Homozygous Heterozygous Homozygous for the for the dominant recessive allele allele Replicated Chromosome Pair of sister chromatids Centromere (DNA that is hidden beneath the kinetochore proteins) One chromatid (dark blue) (a) (b) Kinetochore proteins One chromatid (light blue) Chromatids, Chromosomes… What the… • At the end of S phase, a cell has twice as many chromatids as there were chromosomes in G1 phase – i.e. - human cell • 46 chromosomes in G1 phase • 46 pairs of sister chromatids in G2 phase • chromosome is therefore a relative term – In G1, anaphase, & telophase it refers to the equivalent of one chromatid – In G2, prophase, & metaphase, it refers to a pair of sister chromatids Interphase Two centrosomes, each with centriole pairs Nuclear membrane • Chromosomes are decondensed • chromosomes replicate • The centrosome divides Chromosomes Prophase Microtubules forming mitotic spindle • Nuclear envelope dissociates • Centrosomes move to opposite poles • mitotic spindle apparatus forms Centromere Sister chromatids Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Astral microtubule Metaphase plate Polar microtubule Kinetochore proteins attached to centromere Kinetochore microtubule (d) METAPHASE Spindle Apparatus • Composed of microtubules originated from centrioles • Microtubules are formed polymerization of tubulin proteins • 3 types of spindle microtubules – Aster microtubules • Important for positioning of the spindle apparatus – Polar microtubules • Help to “push” the poles away from each other – Kinetochore microtubules • Attach to kinetochore , at the centromere Kinetochore Spindle Fibers Figure 3.8 Prometaphase Nuclear membrane fragmenting • Spindle fibers bind kinetochores • The two kinetochores on a pair of sister chromatids are attached to kinetochore MTs from opposite poles Spindle pole Mitotic spindle Metaphase Astral microtubule • Pairs of sister chromatids align themselves at the metaphase plate Metaphase plate Kinetochore proteins attached to centromere Polar microtubule Kinetochore microtubule Anaphase Chromosomes • Centromeres separate • Each chromatid, is linked to only one pole • As anaphase proceeds – Kinetochore MTs shorten • Chromosomes move to opposite poles – Polar MTs lengthen • Poles themselves move further away from each other Telophase & Cytokinesis • Chromosomes reach poles & decondense • Nuclear membrane reforms • Quickly followed by cytokinesis – In animals • Formation of a cleavage furrow – In plants • Formation of a cell plate Some Key Points • Mitosis ultimately produces two daughter cells genetically identical to the mother cell – Barring rare mutations • Processes requireing mitotic cell division – Development of multicellularity – Organismal growth – Wound repair – Tissue regeneration