Transcript Slide 1
MITOSIS MITOSIS Mitosis and cell division results in two cells with identical chromosomes and chromosome number as the original cell CELLS GO THROUGH MITOSIS FOR 3 REASONS: 1. GROWTH – AS ORGANISM INCREASES IN SIZE 2. REPLACEMENT OF OLD CELLS THAT SLOUGH OFF 3. REPAIR DAMAGED CELLS MITOSIS pair of centrioles plasma membrane nucleus nuclear envelope chromosomes EARLY PROPHASE two dark blue chromosomes inherited from female parent-- two green inherited from the male parent • mitosis begins • DNA coils and folds to condense LATE PROPHASE • microtubules become assembled & move the two pairs of centrioles to opposite ends of cell • nuclear envelope starts to break up • microtubules then penetrate the nucleus • microtubuoles (“spindle”) will hook onto the two sister chromatids of each chromosome METAPHASE all chromosomes line up at the spindle equator with each sister chromatid facing an opposite pole ANAPHASE TELOPHASE • attachments between the sister chromatids break • there are two clusters of chromosomes, which decondense • microtubuoles shorten pulling each sister chromatid to opposite poles (“reeling in”) • fragments of old membrane fuse to form a new nuclear envelope INTERPHASE Now there are two daughter cells. Each is diploid; its nucleus has two of each type of chromosome, just like the parent cell. Early Prophase Mitosis Begins Duplicated chromosomes begin to condense Late Prophase • New microtubules are assembled • One centriole pair is moved toward opposite pole of spindle • Nuclear envelope starts to break up Late Prophase cont’d • Spindle forms • Spindle microtubules become attached to the two sister chromatids of each chromosome Metaphase • All chromosomes are lined up at the spindle equator • Chromosomes are maximally condensed Anaphase • Sister chromatids of each chromosome are pulled apart • Once separated, each chromatid is a chromosome Telophase • Chromosomes decondense • Two nuclear membranes form, one around each set of unduplicated chromosomes Results of Mitosis • Two daughter nuclei • Each with same chromosome number as parent cell • Chromosomes in unduplicated form Cytoplasmic Division Cytokinesis (cytoplasmic division) is very different for plant and animal cells Two mechanisms: – Cell plate formation (plants) – Cleavage (animals) plant cells have a cell wall that must be built between the two newly formed cells cell wall former spindle equator cell plate vesicles converging cytokinesis in an animal cell (no cell wall – only a plasma membrane) Contractions continue until the ring cuts the cell in two. Mitosis is over, and the spindle is now disassembling. At the former spindle equator, a ring of microfilaments attached to the plasma membrane contracts. As its diameter shrinks, it pulls the cell surface inward. to watch a short animation of mitosis: http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html