The Cell Cycle and Mitosis by jamesdauray

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A Powerpoint lecture covering the entire cell cycle, including mitosis, cell growth, and mechanisms of control.

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									The Cell Cycle
 Introduction to Biology
     The Key Roles of Cell
          Division
• The ability to reproduce is one of the key
  features that separates life from non-life.
• All cells have the ability to reproduce, by
  making exact copies of themselves.
• In unicellular organisms, division of one cell
  reproduces the entire organism
• In multicellular organisms, cell division is needed
  for:
  o Development of an embryo from a sperm/egg
  o Growth
  o Repair
LE 12-2




                    100 µm                        200 µm                    20 µm




     Reproduction            Growth and development        Tissue renewal
    Asexual Reproduction
• Asexual reproduction is reproduction that
  involves a single parent producing an
  offspring.
  o The offspring produced are, in most cases,
    genetically identical to the single cell that
    produced them.
  o Asexual reproduction is a simple, efficient, and
    effective way for an organism to produce a large
    number of offspring.
  o Prokaryotic organisms (like bacteria) reproduce
    asexually, as do some eukaryotes (like sponges)
     Sexual Reproduction
• In sexual reproduction, offspring are
  produced by the fusion of two sex cells – one
  from each of two parents. These fuse into a
  single cell before the offspring can grow.
  o The offspring produced inherit some genetic
    information from both parents.
  o Most animals and plants, and many single-celled
    organisms, reproduce sexually.
   Contrasting
Reproduction Types
            Cell Division
• Cells duplicate their genetic material before
  they divide, ensuring that each daughter cell
  receives an exact copy of the genetic
  material, DNA.
• A dividing cell duplicates its DNA, allocates
  the two copies to opposite ends of the cell,
  and only then splits into daughter cells.
  Cellular Organization of
   the Genetic Material
• A cell’s endowment of DNA (its genetic
  information) is called its genome.
• DNA molecules in a cell are packaged into
  chromosomes.
            Chromosomes
• The genetic information that is passed on from
  one generation of cells to the next is carried
  by chromosomes.
• Every cell must copy its genetic information
  before cell division begins.
• Each daughter cell gets its own copy of that
  genetic information.
• Cells of every organism have a specific
  number of chromosomes.
            Prokaryotic
           Chromosomes
• Prokaryotic cells lack nuclei. Instead, their
  DNA molecules are found in the cytoplasm.
• Most prokaryotes contain a single, circular
  DNA molecule, or chromosome, that contains
  most of the cell’s genetic information.
 Eukaryotic Chromosomes
• In eukaryotic cells, chromosomes are located
  in the nucleus, and are made up of
  chromatin.
• Chromatin is composed of DNA and histone proteins.
• DNA coils around histone proteins to form
  nucleosomes.
• The nucleosomes interact with one another to
  form coils and supercoils that make up
  chromosomes.
     Chromosomes During
         Cell Division
• In preparation for cell division, DNA is replicated and
  the chromosomes condense
• Each duplicated chromosome has two sister
  chromatids, which separate during cell division
• The centromere is the narrow “waist” of the
  duplicated chromosome, where the two chromatids
  are most closely attached
LE 12-4
                                               0.5 µm




               Chromosome
               duplication
               (including DNA
               synthesis)

                        Centromere




                        Sister
                        chromatids


          Separation
           of sister
          chromatids




          Centromeres                Sister chromatids
   Phases of the Cell Cycle
• The cell cycle consists of
  o Mitotic (M) phase (mitosis and cytokinesis)
  o Interphase (cell growth and copying of
    chromosomes in preparation for cell division)
• Interphase (about 90% of the cell cycle) can
  be divided into subphases:
  o G1 phase (“first gap”)
  o S phase (“synthesis”)
  o G2 phase (“second gap”)
LE 12-5


               INTERPHASE




                              S
          G1
                        (DNA synthesis)




                       G2
    G1 Phase: Cell Growth
• In the G1 phase, cells
  increase in size and
  synthesize new proteins
  and organelles.
S Phase: DNA Replication
• In the S (or synthesis)
  phase, new DNA is
  synthesized when the
  chromosomes are
  replicated.
   G2 Phase: Preparing for
        Cell Division
• In the G2 phase, many of
  the organelles and
  molecules required for
  cell division are
  produced.
  M Phase: Cell Division
• In eukaryotes, cell
  division occurs in two
  stages: mitosis and
  cytokinesis.
  o Mitosis is the division of
    the cell nucleus.
  o Cytokinesis is the
    division of the
    cytoplasm.
  Important Cell Structures
    Involved in Mitosis
• Chromatid – each strand of a duplicated
  chromosome
• Centromere – the area where each pair of
  chromatids is joined
• Centrioles – tiny structures located in the cytoplasm of
  animal cells that help organize the spindle
• Spindle – long proteins (part of the cytoskeleton) that
  the centrioles produce
   o Helps move the chromosomes into place.
                Prophase
• During prophase, the
  first phase of mitosis,
  the duplicated
  chromosome
  condenses and
  becomes visible.
               Prophase
• The centrioles move
  to opposite sides of
  nucleus and help
  organize the spindle.
              Prophase
• The spindle forms
  and DNA strands
  attach at a point
  called their
  centromere.
              Prophase
• The nucleolus
  disappears and
  nuclear envelope
  breaks down.
            Metaphase
• During metaphase,
  the second phase of
  mitosis, the
  centromeres of the
  duplicated
  chromosomes line up
  across the center of
  the cell.
            Metaphase
• The spindle fibers
  connect the
  centromere of each
  chromosome to the
  two poles of the
  spindle.
               Anaphase
• During anaphase, the
  third phase of mitosis,
  the centromeres are
  pulled apart and the
  chromatids separate
  to become individual
  chromosomes.
              Anaphase
• The chromosomes
  separate into two
  groups near the poles
  of the spindle.
              Telophase
• During telophase, the
  fourth and final phase
  of mitosis, the
  chromosomes spread
  out into a tangle of
  chromatin.
             Telophase
• A nuclear envelope re-
  forms around each
  cluster of
  chromosomes.
                Telophase
• The spindle breaks apart,
  and a nucleolus becomes
  visible in each daughter
  nucleus.
              Cytokinesis
• Cytokinesis is the division of the cytoplasm.

• The process of cytokinesis is different in animal
  and plant cells.
   Cytokinesis in Animal
           Cells
• The cell membrane is drawn in until the
  cytoplasm is pinched into two equal parts.
• Each part contains its own nucleus and
  organelles.
LE 12-9a




                                           100 µm
           Cleavage furrow




           Contractile ring of         Daughter cells
           microfilaments


              Cleavage of an animal cell (SEM)
    Cytokinesis in Animal
            Cells
• In plants, the cell membrane is not flexible
  enough to draw inward because of the rigid
  cell wall.

• Instead, a cell plate forms between the
  divided nuclei that develops into cell
  membranes.

• A cell wall then forms in between the two new
  membranes.
LE 12-9b




           Vesicles       Wall of                       1 µm
           forming        parent cell
           cell plate            Cell plate   New cell wall




                                               Daughter cells
               Cell plate formation in a plant cell (TEM)
    LE 12-10




Nucleus               Chromatin
                      condensing      Chromosomes                                                                      Cell plate           10 µm
          Nucleolus




  Prophase. The                    Prometaphase. We            Metaphase. The spindle is   Anaphase. The                   Telophase. Daughter
  chromatin is condensing.         now see discrete            complete, and the           chromatids of each              nuclei are forming.
  The nucleolus is                 chromosomes; each           chromosomes, attached       chromosome have                 Meanwhile, cytokinesis
  beginning to disappear.          consists of two identical   to microtubules at their    separated, and the              has started: The cell
  Although not yet visible         sister chromatids. Later    kinetochores, are all at    daughter chromosomes            plate, which will divide
  in the micrograph, the           in prometaphase, the        the metaphase plate.        are moving to the ends of       the cytoplasm in two, is
  mitotic spindle is starting      nuclear envelope will                                   the cell as their               growing toward the
  to form.                         fragment.                                               kinetochore micro-              perimeter of the parent
                                                                                           tubules shorten.                cell.
LE 12-6ca




INTERPHASE   PROPHASE   PROMETAPHASE
LE 12-6ca




INTERPHASE   PROPHASE   PROMETAPHASE
LE 12-6ca




INTERPHASE   PROPHASE   PROMETAPHASE
LE 12-6da




  METAPHASE   ANAPHASE   TELOPHASE AND CYTOKINESIS
LE 12-6da




  METAPHASE   ANAPHASE   TELOPHASE AND CYTOKINESIS
LE 12-6da




  METAPHASE   ANAPHASE   TELOPHASE AND CYTOKINESIS
     Virtual Onion Root Tip
          Mitosis Lab

Click here to start
             Binary Fission
• Prokaryotes (bacteria and archaea) reproduce by a
  type of cell division called binary fission
• In binary fission, the chromosome replicates
  (beginning at the origin of replication), and the two
  daughter chromosomes actively move apart
LE 12-11_1




                                                       Cell wall
                        Origin of
                        replication
                                                         Plasma
                                                         membrane
                                      E. coli cell   Bacterial
                                                     chromosome
 Chromosome                     Two copies
 replication begins.            of origin
 Soon thereafter,
 one copy of the origin
 moves rapidly toward
 the other end of the cell.
LE 12-11_2

                                                       Cell wall
                        Origin of
                        replication
                                                         Plasma
                                                         membrane
                                      E. coli cell   Bacterial
                                                     chromosome
 Chromosome                     Two copies
 replication begins.            of origin
 Soon thereafter,
 one copy of the origin
 moves rapidly toward
 the other end of the cell.



                                 Origin               Origin
 Replication continues.
 One copy of the origin
 is now at each end of
 the cell.
LE 12-11_3
                                                                  Cell wall
                                    Origin of
                                    replication
                                                                     Plasma
                                                                     membrane
                                                  E. coli cell   Bacterial
                                                                 chromosome
             Chromosome                    Two copies
             replication begins.           of origin
             Soon thereafter,
             one copy of the origin
             moves rapidly toward
             the other end of the cell.



                                             Origin               Origin
             Replication continues.
             One copy of the origin
             is now at each end of
             the cell.




             Replication finishes.
             The plasma membrane
             grows inward, and
             new cell wall is
             deposited.


             Two daughter
             cells result.
   The Evolution of Mitosis
• Since prokaryotes evolved before eukaryotes, mitosis
  probably evolved from binary fission
• Certain protists exhibit types of cell division that seem
  intermediate between binary fission and mitosis
LE 12-12
                                              Bacterial
                                              chromosome


           Prokaryotes

                                       Chromosomes


                                            Microtubules



                                           Intact nuclear
                                           envelope
           Dinoflagellates (Type of plankton)


                                            Kinetochore
                                            microtubules


                                            Intact nuclear
                                            envelope

           Diatoms (Type of Algae)

                                           Kinetochore
                                           microtubules

                                           Centrosome


                                           Fragments of
                                           nuclear envelope
           Most eukaryotes
     The Cell Cycle Control
            System
• The sequential events of the cell cycle are directed
  by a distinct cell cycle control system, which is similar
  to a clock
• The clock has specific checkpoints where the cell
  cycle stops until a go-ahead signal is received
LE 12-14
                            G1 checkpoint




                                Control
                                system         S
                     G1




                          M               G2




      M checkpoint
                          G2 checkpoint
• For many cells, the G1 checkpoint seems to
  be the most important one
• If a cell receives a go-ahead signal at the G1
  checkpoint, it will usually complete the S, G2,
  and M phases and divide
• If the cell does not receive the go-ahead
  signal, it will exit the cycle, switching into a
  nondividing state called the G0 phase
LE 12-15




                                                  G0

     G1 checkpoint




                             G1                               G1


           If a cell receives a go-ahead   If a cell does not receive a
           signal at the G1 checkpoint,    go-ahead signal at the G1
           the cell continues on in the    checkpoint, the cell exits the
           cell cycle.                     cell cycle and goes into G0, a
                                           nondividing state.
• An example of external signals is density-
  dependent inhibition, in which crowded cells
  stop dividing
• Most animal cells also exhibit anchorage
  dependence, in which they must be
  attached to a substratum (connective tissue)
  in order to divide
LE 12-18a
                             Cells anchor to dish surface and
                             divide (anchorage dependence).



                             When cells have formed a complete
                             single layer, they stop dividing
                             (density-dependent inhibition).



                             If some cells are scraped away, the
                             remaining cells divide to fill the gap and
                             then stop (density-dependent inhibition).




                                           25 µm
            Normal mammalian cells
LE 12-18b




                 Cancer cells do not exhibit
                 anchorage dependence
                 or density-dependent inhibition.




                               25 µm
  Cancer cells
    Loss of Cell Cycle
  Controls in Cancer Cells
• Cancer cells do not respond normally to the
  body’s control mechanisms
• Cancer cells form tumors, masses of abnormal
  cells within otherwise normal tissue
• If abnormal cells remain at the original site,
  the lump is called a benign tumor
• Malignant tumors invade surrounding tissues
  and can metastasize, exporting cancer cells
  to other parts of the body, where they may
  form secondary tumors
LE 12-19




                                                              Lymph
           Tumor                                              vessel


                                                               Blood
           Glandular                                           vessel
           tissue
                                                                        Metastatic
                                               Cancer cell              tumor
A tumor grows from a   Cancer cells invade   Cancer cells spread         A small percentage
single cancer cell.    neighboring tissue.   through lymph and           of cancer cells may
                                             blood vessels to            survive and establish
                                             other parts of the          a new tumor in another
                                             body.                       part of the body.

								
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