Mitosis I BIO 105 Cr.4
UW - L
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This page Class Notes was uploaded by MaKena Betler on Tuesday November 3, 2015. The Class Notes belongs to BIO 105 Cr.4 at University of Wisconsin - La Crosse taught by a professor in Fall 2015. Since its upload, it has received 21 views. For similar materials see General Biology in Biology at University of Wisconsin - La Crosse.
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Date Created: 11/03/15
Lecture 23 Mitosiil What happens when the cell cycle goes wrong 0 Cancer failure to control cell division Eukaryotic cells follow the cell cycle 0 M Mitosis used to divide the chromosomes and the cellular organelles in the daughter cells 0 G1 Gap 1 Cells take in nutrients and grow Cells can leave the cycle and enter a resting state called G0 0 G2 Gap 2 Following DNA replication the cells generally stop to take in more nutrients and grow 0 S DNA synthesis DNA replication occurs once a cell commits to enter the cell cycle 0 START The point when a cell commits to the cell cycle Mphase is the only microscopically distinct phase of the cell and can be split into ve mitotic phases along with cytokinesis o Cytokinesis is part of the mphase but is not one of the phases of mitosis Cytokinesis overlaps with anaphase and telophase ends with two fully divided cells both in G1 0 The genome contains all the genes encoded in a cell s DNA 0 Bacterial genomes Contained on a single chromosome made from circular doublestranded DNA 210 million base pairs Mbp o Eukaryotic genomes Contained on multiple chromosomes 240 each made from linear doublestranded DNA in proteinDNA complexes chromatin 10 Mbp gt100 Gbp Genome size and gene number are not usually correlated In a typical eukaryote most of the gene in noncoding Humans have 46 chromosomes and are diploid two copies of 23 chromosomes 0 Missing chromosome monosomy usually fatal in embryotic stage 0 Extra chromosome trisomy also fatal except in smallest chromosomes o Gamete cells sperm egg have only 23 chromosomes and are called haploid Chromosomes exist in somatic diploid cells as the two copies called homologous chromosomes 0 One from mom one from dad Homologous chromosom s Centromere o The number of chro o 0 es varies enormously from species to species Eukaryotic chromosomes are composed of chromatin complex of DNA 40 and proteins 60 o The DNA helix negatively charged is wrapped around positively charged proteins called histones o 200 nucleotides of DNA coil around a core of 8 histones forming a nucleosome Chromosome in use cell growth chromatin Chromosome in mitosis division chromosomes 0 DNA is replicated in S synthesis phase marking the beginning of the cell cycle before mitosis Replicated chromosomes consist of two sister chromatids held together at the centromere by proteins called cohesions Sister Sister HomOIOQOUS chromatid chromatids chromosom es Cytoskeleton splits a cell into daughter cells during mitosis o Eukaryotic chromosomes replicate 2 exact copies o Eukaryotic cytoskeleton changes shape to accomplish chromosome segregation quotmitosisquot and division of the cytosol quotcytokinesisquot Spindle microtubules segregate chromosomes during mitosis Actin contractile ring divides cell cytosol during cytokinesis Prophase is when the 1 chromatin condenses and the 2 normal cytosolic aster array of microtubules changes into the mitotic spindle o Chromatin already replicated condenses into the mitotic chromosomes 0 lnterphase microtuble array breaks down while the MTOC duplicates and each copy moves to opposite poles of the nucleus 0 Spindle poles ew microtubule array is assembled into mitotic Spmdle Chromosome 2 DNA Kinetochore Centromere Protein structure segment of DNA for attaching where sister chromatid to chromatids microtubules to remain attached 0 ln prophase the interphase microtubules are disassmebled and reassembled to form a spindle o In interphase microtubules are tracks for organelles to move on o The Microtubule Organizing Center MTOC is duplicated before mitosis and in prophase the 2 MTOCs move apart and become the spindle poles o In mitosis microtubules are trackes for chromosomes to move one Prometaphase is when nuclear envelope breaks down 0 Spindle microtubules seek the kinetochore a structure that assembles at each centromere 0 Once a microtubule binds to a kinetochore it is now called a kinetochore micrtubule Each sister chromatid will typically have multiple kinetochore microtubules bound to each kinetochore o Other quotinterpolarquot microtubules continue to grow reinforcng the spindle and helping to separate the poles Transition between prophase and prometaphase 0 Nuclear envelope breaks down so spindle can attach to the chromosomes ln prometaphase sister chromatids must attach to microtubules from opposite poles Metaphase is when the chromosomes get aligned in the middle 0 Once kinetochore microtubules have grabbed both kinetochores they play quottug of warquot with the sister chromatids o Chromosomes line up in the middle of the cell 0 Polar microtubules hae been growing longer pushing the spindle poles apart establishing the midpoint for the chromosomes 0 Kinetochores of sister chromatids are attached to opposite poles via kinetochore microtubules KMTs 0 Tracks to follow to poles new homes Anaphase is when the sister chromatids separate and cytokinesis begins 0 Shortening of the kindetochore microtubules result in the segragation of chromosomes to the opposite sides of the cell 0 New actin and myosin array is forming on the inner face of the plasma membrane at the midpoint called the contactile ring Telephase is quotcleanupquot when things get returned to the interphase state 0 Sister chromatids decondense while the nuclear envelope reforms from the endoplasmic reticulum o Kinetochore microtubules disassemble lnterphase aster array begins to reform on each side 0 Myosin uses ATP energy to contract the contractile ring constricting the membrane around the midbody The contractile ring in animal cells results in the quotcleavage furrowquot seen in micrographs 0 New membrane must be added to resolve the midbody and to provide the necessary surface area that must be added to cover both daughter cells 0 At the end of the cytokinesis both daughter cells have the typical interphase cytoskeletal array and have the interphase number of chromosomes
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