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Date Created: 09/22/15
L112 Cell Division Mitosis Reece et al Chapter 12 Mitosis Multicellular eukaryotes depend on cell division for Development from a fertilized cell Growth Repair Mitosis results in daughter cells with identical genetic information DNA Figure 122 a Reproduction b Growth and develop ment u 9222015 c Tissue renewal Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cell 5 genome A genome can consist of a single DNA molecule common in prokaryotic cells or a number of DNA molecules common in eukaryotic cells DNA molecules in a cell are packaged into chromosomes Eukaryotic chromosomes consist of chromatin a complex of DNA and protein nucleosomes that condenses during cell division Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Somatic cells nonreproductive cells have two sets of chromosomes Gametes reproductive cells sperm and eggs have half as many chromosomes as somatic cells Distribution of Chromosomes During Eukaryotic Cell Division In preparation for cell division DNA is replicated and the chromosomes condense Each duplicated chromosome has two sister chromatids joined copies of the original chromosome attached along their lengths by cohesins The centromere is the narrow waist of the duplicated chromosome where the two chromatids are most closely attached Figure 124 Sister chromatids Centromere 05 m 9222 15 Fi ure1253 9 Chromosomal Chromosomes DNA molecules Centromere Chromosome arm Chromosome duplication Sister chromatids Separation of sister chromatids 9222015 Phases of the Cell Cycle The cell cycle consists of Mitotic M phase mitosis and cytokinesis lnterphase lnterphase about 90 of the cell cycle can be divided into subphases G1 phase first gapquot S phase synthesis G2 phase second gapquot Iigure 126 4 Figure 1216b Cdk 3a Degraded cyclin Cyclin is degraded C MPF checkpoint b Molecular mechanisms that help regulate the cell cycle ageinmnaae Mill 3 Figure 127a It 1 I i i 1quot tquotul39 ra I I 39 NFC a ixri f 39 Itji3951f AL J I 2 32 of lnterphase Prometaphase ce tr S meS Chromosomes Early mitotic A Fragments Nonkinetochore pairs uncondensed Cemromere envelope x 16quot 7 T 4 I 9 I Plasma Nuclear membrane 9222015 erIVGIOpe Two sister chromatids Kinetochore Kinetochore of one chromosome microtubule Nucleolus Figure 127b 10pm Metaphase Telophase and Cytokinesis Metaphase Cleavage Nucleous plate furrow forming Daughter e chromosomes Nuclear Q y 1 hr Spmdle Centrosome at envelope 9222o15 one Spindle POIG forming The Mitotic Spindle A Closer Look The mitotic spindle is a structure made of microtubules that controls chromosome movement during mitosis In animal cells assembly of spindle microtubules begins in the centrosome the microtubule organizing center The centrosome replicates during interphase forming two centrosomes that migrate to opposite ends of the cell during prophase and prometaphase During prometaphase some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes Kinetochores are protein complexes associated with centromeres At metaphase the chromosomes are all lined up at the metaphase plate a plane midway between the spindle 5 two poles Figure 128 Centrosome Metaphase plate imaginary Sister chromatids Kineto chores Microtubules Overlapping nonkinetochore microtubules Kinetochore microtubules Chromosomes Q Centrosome 39 v I I V quot s var 39 v V I quot 39 39 1 V c I A I 39 39 D r v 39 39 r V I a a cl 39 v U oc 39 t I I x 1 Pm 05 IJm srwgzzfzerse39Wu a1 a 5 Mg In anaphase the cohesins are cleaved by an enzyme called separase Sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell The microtubules shorten by depolymerizing at their kinetochore ends Figure 129b Resu s Conclusion Chromosome movement Motor protein Chromosome Microtubule 9222Q15 Kinetoohore 1quot Tubulin 39 subun s Nonkinetochore microtubules from opposite poles overlap and push against each other elongating the cell In telophase genetically identical daughter nuclei form at opposite ends of the cell Cytokinesis begins during anaphase or telophase and the spindle eventually disassembles Figure 1210 a Cleavage of an animal cell SEM b Cell plate formation in a plant cell TEM 39 plaid W a quot75 h 1 it 4 r J C 2 fquot 30 39H Ttd PR 39 f39 a A 7 3 quot quot 5 quot a wg 39 vquot57 39 v3 gt39 I 39 r quot39391 I u my 39 gx JJg oquot L 39 AL quotI 39 uk x 44 5 Ar 3939 i 13 C 1 u A 3 r Urquot ulp nquot M39n V f v 39 19 33 m x g u 1 r 39 I 4 39 3 439 39 2m 41 him in I 3991 39 ru tailbx t 3939 4 gz K 9 39g ygt 7 rmlyL MW J 39 55 39z3quotquot r v i 39 r quot7ampamp af x f21 hi gt v 39 WW H35quot 39 quot l A L sY Wm dashWWW Viv 39 539 39 u g 39 n g In Vesicles Wall of parent cell 1 pm forming cell plate a New cell wall Contractile ring of Daughter cells microfilaments Daughter cells 9222015 The eukaryotic cell cycle is regulated by a molecular control system The frequency of cell division varies with the type of cell These differences result from regulation at the molecular level 39 Cancer cells manage to escape the usual controls on the cell cycle The sequential events of the cell cycle are directed by a distinct cell cycle control system which is similar to a clock The cell cycle control system is regulated by both internal and external controls The clock has specific checkpoints where the cell cycle stops until a go ahead signal is received Figure 1216b Cdk 3a Degraded cyclin Cyclin is degraded C MPF checkpoint b Molecular mechanisms that help regulate the cell cycle ageinmnaae Mill 3 The Cell Cycle Clock Cyclins and CyclinDependent Kinases Two types of regulatory proteins are involved in cell cycle control cyclins and cyclindependent kinases Cdks The activity of a Cdk rises and falls with changes in concentration of its cyclin partner MPF maturationpromoting factor is a cyclinCdk complex that triggers a cells passage past the G2 checkpoint into the M phase For many cells the G1 checkpoint seems to be the most important If a cell receives a goahead signal at the G1 checkpoint it will usually complete the S 62 and M phases and divide If the cell does not receive the goahead signal it will exit the cycle switching into a nondividing state called the G0 phaseeg quiescent heart muscle cells amp nerve cells Normal cells Anchorage dependenceto divide they must be attached to a substratum Densitydependent inhibition checks the growth of cells at an optimal denshy 39 Cancer cells exhibit neither type of regulation of their division Figure 1219 Anchorage dependence cells require a surface for division Densitydependent inhibition cells form a single layer Densitydependent inhibition cells divide to fill a gap and then stop a Normal mammalian cells b Cancer cells 9222015 Loss of Cell Cycle Controls in Cancer Cells Cancer cells do not respond normally to the body s control mechanisms Cancer cells may not need growth factors to grow and divide They may make their own growth factor They may convey a growth factor s signal without the presence of the growth factor They may have an abnormal cell cycle control system External factors that influence cell division include specific growth factors Growth factors are released by certain cells and stimulate other cells to divide Plateletderived growth factor PDGF is made by blood cell fragments called platelets A normal cell is converted to a cancerous cell by a process called transformation If abnormal cells remain only at the original site the lump is called a benign tumor If abnormal cells move away from the initial site to other parts of the body metastasis Figure 1220 1 L0 Breast cancer cell colorized SEM Metastatic Lymph vessel Tumor Blood vessel A 9 quot Glandular cancer ssue 09quot 0 A tumor grows 9 Cancer cells invade 9 Cancer cells spread A small percentage from a single neighboring tissue through lymph and of cancer cells may cancer cell blood vessels to other metastasize to parts of the body another part of the body 9222 15 Figure 12200 Breast cancer cell colorized SEM 9222Q15
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