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					Cell Growth and Division
             Honors Biology
                Chapter 10
Cell Growth

Living things grow larger due to an
 increase in cells
Larger the cell, the more demands on the
 DNA and the more transport of water and
 nutrients across the membrane
The surface area to volume ratio must also
 be maintained.
 Cell Growth
Before the cell gets too big in size, it must
 divide into 2 new daughter cells via a process
 known as cell division
In order to divide, the cell must make a copy
 of its DNA so each cell has a set of
 instructions of how the body functions




DNA Replication
Cell Division

Occurs in 2 main stages
 1. mitosis – division of nucleus
 2. cytokinesis – division of cytoplasm
Considered to be asexual since the two
 daughter cells are genetically identical to
 the parent cell
Source of new cells as organism grows
 and develops
Chromosomes

Made of DNA and proteins
Cells of every organism have a specific
 number of chromosomes
 humans = 46 carrot = 18 fruit fly = 8
Chromosomes are only visible during cell
 division, these structures form to compact
 the DNA to make it easy to divide
 Chromosome Structure
 Each chromosome consists of 2 identical “sister” chromatids
 When the cell divides, the sister chromatids separate from
  each other. One chromatid goes to each of the 2 new cells
 Each pair of chromatids are attached by the centromere. The
  centromere is usually located near the middle of the chromatid
 The human body contains 46 chromosomes and 46
  centromeres, each of which contain 2 chromatids


                      Short arm




                      Long arm


                         One chromosome with 2
                         identical sister chromatids
 Cell Cycle

 During the cell cycle, a cell grows, prepares for
  division, and divides to form 2 new identical
  daughter cells, each of which then begin the cycle
  again.
 The cell cycle consists of 4 phases
  1. M Phase: (mitosis phase) mitosis and cytokinesis
  2. G1 Phase: (gap phase) growth and activity
  3. S Phase: (synthesis phase) DNA replication
  4, G2 Phase: (gap phase) growth and activity
 G1, S and G2 all used to be group together and
  called interphase
 Cell Cycle          G1 Phase




M Phase




                                S Phase
          G2 Phase
Interphase
 Cell spends more time in interphase than M
  phase
1. G1 Phase – Most growing occurs. Cells
  increase in size and synthesize new proteins
  and organelles
2. S Phase – Chromosomes are replicated. Key
  proteins are synthesized
3. G2 Phase – Shortest of the three phases.
  Organelles and molecules required for division
  are produced. When the cell completes this
  phase it is ready to enter the M phase and begin
  the process of cell division
 Mitosis
 Involves the centrioles (cell organelles made of
  proteins and microtubules) of the cell
 Occurs in four stages
  1. prophase – chromosomes appear and nuclear
  envelope breaks down
  2. metaphase – chromosomes line up across
  center of cell
  3. anaphase - sister chromatids separate into
  separate cells
  4. telophase – chromosomes gather at opposite
  ends of two cells and two new nuclear envelopes
  begin to form
                                During Interphase the chromosomes are
Interphase                      not visible. The cell grows and replicates its
                                DNA and centrioles
                                         Spindle
                                         forming
    Centrioles




                  Nuclear    Chromatin   Centromere                         Centriole
                                                        Chromosomes
                 envelope
                                                      (paired chromatids)
                       Interphase        Prophase               Spindle

                  Cytokinesis                                  Centriole


                                            Individual            Metaphase
                            Telophase     chromosomes

      Nuclear                     Anaphase
     envelope
     reforming
Prophase
 Longest phase of mitosis
 Chromatin condenses and chromosomes
  become visible
 The nuclear envelope begins to break down
 Centrioles separate and take positions on
  opposite sides of the cell
 The spindle, a microtubule structure that helps
  separate the chromosomes, begins to form
Prophase
                                         Spindle
                                         forming
    Centrioles




                  Nuclear    Chromatin   Centromere                         Centriole
                                                        Chromosomes
                 envelope
                                                      (paired chromatids)
                       Interphase        Prophase               Spindle

                  Cytokinesis                                  Centriole


                                            Individual            Metaphase
                            Telophase     chromosomes

      Nuclear                     Anaphase
     envelope
     reforming
Metaphase

Chromosomes line up across the center of
 the cell.
Microtubules connect the centromere of
 each chromosome to the two poles of the
 spindle
Metaphase
                                         Spindle
                                         forming
    Centrioles




                  Nuclear    Chromatin   Centromere                         Centriole
                                                        Chromosomes
                 envelope
                                                      (paired chromatids)
                       Interphase        Prophase               Spindle

                  Cytokinesis                                  Centriole


                                            Individual            Metaphase
                            Telophase     chromosomes

      Nuclear                     Anaphase
     envelope
     reforming
Anaphase
The centromeres that join the sister
 chromatids of the chromosome split and
 allow the sister chromatids to separate
 and become individual chromosomes
The chromatids continue to move until
 they have separated into two groups near
 the poles of the spindle
Anaphase ends when the chromatids stop
 moving
Anaphase
                                        Spindle
                                        forming
   Centrioles




                 Nuclear    Chromatin   Centromere                         Centriole
                                                       Chromosomes
                envelope
                                                     (paired chromatids)
                      Interphase        Prophase               Spindle

                 Cytokinesis                                  Centriole


                                           Individual            Metaphase
                           Telophase     chromosomes

     Nuclear                     Anaphase
    envelope
    reforming
Telophase
 Final stage of mitosis
 Chromosomes begin to loosen and into a tangle
  of dense material
 Two new nuclear envelopes begin to reform
  around the two clusters of chromosomes
 The spindle begins to break apart and a
  nucleolus becomes visible in each daughter
  nucleus
 Mitosis is now complete, 2 nuclei are formed, but
  the cells are not yet separated
Telophase
                                         Spindle
                                         forming
    Centrioles




                  Nuclear    Chromatin   Centromere                         Centriole
                                                        Chromosomes
                 envelope
                                                      (paired chromatids)
                       Interphase        Prophase               Spindle

                  Cytokinesis                                  Centriole


                                            Individual            Metaphase
                            Telophase     chromosomes

      Nuclear                     Anaphase
     envelope
     reforming
Cytokinesis
 Separation of cytoplasm within a single cell
 Typically occurs at the same time as telophase
 Cell membrane is drawn inward until the
  separation of the cytoplasm into two nearly
  equal parts
 Each part contains its own nucleus and
  organelles
 In plants, a cell plate forms midway between the
  divided nuclei and a cell wall begins to appear in
  the cell plate
Cytokinesis
                                         Spindle
                                         forming
    Centrioles




                  Nuclear    Chromatin   Centromere                         Centriole
                                                        Chromosomes
                 envelope
                                                      (paired chromatids)
                       Interphase        Prophase               Spindle

                  Cytokinesis                                  Centriole


                                            Individual            Metaphase
                            Telophase     chromosomes

      Nuclear                     Anaphase
     envelope
     reforming
Mitosis and Cytokinesis Video Segment


    ..\..\bio CD\Chapter 10A.mpg
Did you know????

 All of the DNA in an adult human body
 could fit inside one ice cube, but if
 unwound, stretched out and joined end to
 end, it could reach from the earth to the
 sun and back again approximately 400
 more times.
Homework Assignment
This will be due tomorrow, start it in class
 now because it is a long assignment!!!

Suppose you were small enough to hitch a
 ride on a chromosome located in an
 animal cell that goes through mitosis and
 cytokinesis. Describe what you would see
 happening during EACH phase of the
 process

				
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