Cytology Lecture 10: Cell Division Mitosis PDF

Cytology   Lecture:  10   cell  division  mitosis        Mitosis  +  Cytokinesis  =  Cell  division   Most  cells  in  all  eukaryo6c  organisms  will  divide   many  6mes  throughout  the  life  of  the  orga...

Cytology   Lecture:  10   cell  division  mitosis        Mitosis  +  Cytokinesis  =  Cell  division   Most  cells  in  all  eukaryo6c  organisms  will  divide   many  6mes  throughout  the  life  of  the  organism     – Mitosis  is  the  process  by  which  a  cell  duplicates  its  gene6c   materials  (chromosomes)  prepares  for  cell  division   – Cytokinesis  is  the  division  of  the  rest  of  the  cell  into  two   different  daughter  cells   – Prokaryotes  also  divide  through  binary  fission,  but  this  is   NOT  mitosis/cytokinesis   In  animals,  cell  division  occurs  during  embryonic   development,  growth,  and  wound  healing   Errors  during  cell  division  can  cause  cell  death  or   cancer    Mitosis  reorganizes  DNA  in  the  cell   Prior  to  mitosis,  the  cell  creates  an  exact  duplicate  of   its  DNA  material   During  mitosis,  the  two  copies  are  reorganized,   repackaged  into  two  sets  of  chromosomes,  and   divided  to  opposite  ends  of  the  cell   In  most  organisms,  mitosis  is  immediately  followed   by  cytokinesis  (the  cell  body  dividing  in  two)   The  original  cell  (mother  cell)  is  iden6cal  to  the  two   resul6ng  cells  (daughter  cells)    Mitosis  vocabulary   Nucleus  –  loca6on  of  DNA  inside  the  cell   Nuclear  envelope  –  the  membrane  that  separates  the  nucleus  from  the  cytoplasm   DNA  –  an  incredibly  long  molecule  that  contains  gene6c  blue  prints  for  cell  behavior   Chroma6n  –  a  loosely  bundled  coil  of  DNA.    Most  of  the  6me,  DNA  is  organized  in  this  form,   “  a  loose  rope”   Histones  –  proteins  which  hold  a  DNA  strand  together  in  the  form  of  chroma6n   Chromosome  –  a  highly  organized  form  of  chroma6n,  “a  6ghtly  wrapped  and  carefully   knoPed  rope  ”   – Each  chromosome  is  composed  of  two  iden6cal  parts  called  chroma6ds   – Chroma6ds:  two  halves  of  a  chromosome  which  contain  the  same  gene6c  informa6on     – DNA  exists  in  the  form  of  chromosomes  only  during  mitosis   – Each  chromosome  looks  like  an  X     Centromere  –  a  bundle  of  proteins  which  connects  the  two  chroma6ds  of  a  chromosome,   the  “knot  at  the  center  of  the  X“   Microtubules  –  part  of  a  cell’s  cytoskeleton.    These  are  tubes  of  protein  which  use  to  pull   chromosomes  apart  and  to  opposite  ends  of  a  cell  during  mitosis.    They  are  powered  by  ATP!   Mito6c  spindle  –  How  microtubules  are  organized  during  mitosis.    This  is  a  collec6on  of   microtubule  fibers  which  is  formed  to  coordinate  the  pulling  of  apart  of  chromosomes.       Metaphase  plate  –  the  line  along  which  chromosomes  are  lined  up  during  mitosis.    This   arrangement  is  coordinated  by  the  mito6c  spindle.     Chromosome  Structure    Mitosis – For description, mitosis is usually broken into five sub phases: 1-prophase, prometaphase 2-metaphase, 3-anaphase, and 4-telophase.  By late interphase, the chromosomes have been duplicated but are loosely packed. The centrosomes have been duplicated and begin to organize microtubules into an aster (“star”).  Prophase In prophase, the chromosomes are tightly coiled, with sister chromatids joined together. The nucleoli disappear.  Prophase The mitotic spindle begins to form and appears to push the centrosomes away from each other toward opposite ends (poles) of the cell.  Prometaphase During prometaphase, the nuclear envelope fragments and microtubules from the spindle interact with the chromosomes. Microtubules from one pole attach to one of two kinetochores, special regions of the centromere, while microtubules from the other pole attach to the other kinetochore.  Metaphase The spindle fibers push the sister chromatids until they are all arranged at the metaphase plate, an imaginary plane equidistant between the poles, defining metaphase.  Anaphase At anaphase, the centromeres divide, separating the sister chromatids. Each is now pulled toward the pole to which it is attached by spindle fibers. By the end, the two poles have equivalent collections of chromosomes.  Telophase At telophase, the cell continues to elongate as free spindle fibers from each centrosome push off each other. Two nuclei begin for form, surrounded by the fragments of the parent’s nuclear envelope. Chromatin becomes less tightly coiled.  Cytokinesis, Cytokinesis, division of the cytoplasm, begins after formation of two nuclei and two new cells formed ,which resemble to mother cell and contain 2n chromosome. Fig. 2 Fig. 2.