CELL DIVISION Unit 3 Part 2 – The Cell

Cell Cycles  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 Prokaryotic CellsEukaryotic Cells

Eukaryotic Cell Cycle  3 Stages:  Interphase G1 – Growth S – DNA Synthesis G2 – Growth  Mitosis – Division of Nucleus P – Prophase M – Metaphase A – Anaphase T – Telophase  Cytokinesis Division of cytoplasm

Terms to know for Mitosis  Chromatin  The stringy, filamentous, working form of DNA.  ReplicatChromosome  One of the 2 copies of coiled DNA.  ed Chromosome  The 2 identical copies of a of DNA molecule attached by the centromere.  Sister Chromatid  1 individual strand of the attached identical copies of DNA.  Non-Replicated Chromosome  Single strand of DNA; unattached and coiled.  Spindle Fibers  Fibers that are attached to centrioles to help pull apart chromosomes  Centrioles  Organelles that aid in pulling apart chromosomes  Centromere  Structure that holds the replicated chromosomes together

Sister Chromatids Replicated Chromosome Centromere Non-Replicated Chromosome Chromosome

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.  This is when the cell functions as the type of cell it is and then prepares to divide.  The LONGEST phase of the cell cycle.  90% of the cell’s life is spent in Interphase. The cell does not look unique. The nucleus and the nucleolus are visible; The nuclear membrane is intact and visible.

Interphase (G1, S, G2)

Mitosis (PMAT)  Mitosis:  The nucleus of a cell is divided into two nuclei with the same number of chromosomes (2n = diploid.)  Consists of 4 phases Prophase Metaphase Anaphase Telophase

Prophase  Longest phase of Mitosis.  Chromatin coils and forms chromosomes.  Nuclear envelope breaks down.  Centrioles migrate toward opposite ends.  Spindle fibers form and attach to the centromeres.

Metaphase  Chromosomes line up in the middle of the cell.

Anaphase  Centromeres of each chromosome split.  Spindle fibers contract and separate the two sister chromatids pulling them to opposite poles.  Each chromatid becomes a separate (non-replicated) chromosome in each daughter cell.

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

Cytokinesis  NOT part of mitosis.  The cytoplasm divides into two cells.  Cell membrane reforms.  In plant cells the cell wall reforms and the cell membrane is laid down.

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