Cell Cycle

1. interphase
2. mitosis
3. cytokinesis

Cell Cycle

1. Interphase

           period of cell growth & development

  largest part of cell life

  cell prepares to divide

  DNA in the form of chromatin – thin threads of DNA

  3 Phases of Interphase

cell size doubles

enzymes & organelles double in number

rapid protein synthesis

*DNA Replicates*

                  3.  G₂ Phase

                        cell undergoes rapid growth that prepares it for mitosis

                        necessary enzymes & structures are synthesized

                        centrioles replicate

2.      Mitosis

               Division of cell nucleus

               Produces 2 identical nuclei with the same number of chromosomes

               A continuous process divided into phases

4 Phases of Mitosis

1.  Prophase

1^st phase

longest phase

divided into early, middle, & late stages

Early – chromosomes appear – double stands of DNA – 2 chromatids held

             together by a centromere

             nucleolus & nuclear membrane disappear

             centrioles move to opposite ends (poles) of the cell

Middle – spindle fibers form, composed of microtubules

                2 types of spindle fibers

                 1.  polar fibers – extend across the cell from centriole to centriole         

                                                                  from pole to pole

                       2.   kinetochore fibers – extend from the centromere of a

                                                              chromosome to the centrioles

                                                              controls chromosome movement

                                                              shorten to pull chromatids to poles

   Late – asters form – protein fibers that radiate from each centriole, not found

                                    in plant cells

                                    consists of astral rays and centrioles

2.      Metaphase

     Chromosomes line up along the middle (equator) of  the cell

     Kinetochore fibers move chromosomes to middle (equator) of cell

3.  Anaphase

            Centromeres divide

            Chromatids separate & move toward opposite poles, rapid movement

             Polar fibers, using ATP, push each other to opposite poles

             Kinetochore fibers shorten & pull chromatids toward the pole

             Cytokinesis begins – division of cytoplasm

4.  Telophase

           2 identical sets of chromatids are clustered at opposite sides of the cell

     Reverse of prophase

        Spindle disappears

        Nucleus reappears

        Nuclear membrane reappears

        Chromatids revert to chromatin

        Nucleolus reappears

     Cytokinesis completed

Mitosis Triggers

(causes of cell division)

1.      too much cytoplasm for the nucleus to control

2.      too much cytoplasm (volume) for the surface area – reduces cellular transport

                      Functions of Mitosis

1.      ensure genetic continuity – make sure every cell has all the genetic

      material – so all the cells have all the information they need

2.      growth

3.      repair

4.      asexual reproduction in unicellular organisms

5.      produces diploid cells – have all the genetic material

3. Cytokinesis

           Division of cytoplasm

           Begins during anaphase of mitosis

           Completed during telophase of mitosis

           Forms 2 cells – separates the 2 nuclei formed during mitosis

           Separates organelles

           The 2 cells are usually equal in size

      Animal cells – cytokinesis is completed by a cleavage furrow – pinching of

                              Cytoplasm

      Plant cells – cytokinesis is completed by a cell plate – forms from vesicles formed

                          by Golgi apparatus, forms cell wall