Unit 3 Part 2 – The Cell

PROKARYOTIC CELLSEUKARYOTIC CELLS  No nucleus.  No membrane bound organelles. (ex. mitochondria, vacuole, chloroplast) A.) Cell division takes place in 2 steps:  1.) DNA is copied.  2.) Cell splits by binary fission.  Contain a nucleus and organelles.  Have a cell cycle. Repeating sequence of growth and division.

 5 Stages G1  First growth phase S  Synthesis phase G2  Second growth phase Mitosis  Cell division Cytokinesis  Division of cytoplasm

 This is when the cell is preparing to divide.  The LONGEST phase of the cell. cycle  90% of the cell’s life is spent in Interphase  G1 – first growth phase: The cell doubles in size and the organelles double.  S – synthesis phase: the DNA that makes up the chromatin is copied (DNA replication) this is the longest phase of interphase.  G2 – second growth phase: Growth and preparation for mitosis.

 Mitosis The nucleus of a cell is divided into two nuclei with the same number of chromosomes. Consists of 4 phases  Prophase  Metaphase  Anaphase  Telophase

 Chromosome Single piece of coiled DNA.  Replicated Chromosome A single piece of DNA that has been copied through DNA replication.  Sister Chromatids 2 identical strands of DNA.  Non-Replicated Chromosome Single strand of DNA before it is copied.  Spindle Fibers Fibers that extend from the centrioles and help to pull apart chromosomes.  Centrioles Organelles that aid in pulling apart replicated chromosomes.  Centromere Structure that holds the replicated chromosomes together.

Sister Chromatids Replicated Chromosome Centromere Non-Replicated Chromosome

 Longest phase of MITOSIS Chromatin coils and forms chromosomes Nuclear envelope breaks down Spindle fibers form and stretch from one end of the cell to the other  They attach to the centrioles  They help to pull the cell apart

 Chromosomes line up in the middle of the cell.

 Centromere of each chromosome splits.  Two sister chromatids separate and move to opposite poles.  Each chromatid becomes separate (non-replicated) chromosome in each daughter cell.

 Last stage of Mitosis.  Chromosomes at each pole uncoil and become chromatin.  Nuclear envelope reforms.  Spindle fibers break down.

 NOT part of mitosis.  The cytoplasm divides into two cells.  Cell membrane reforms.  In plant cells the cell wall reforms.

Video 1  Click the image to play the video segment. Video 1 Animal Cell Mitosis