CELL DIVISION Cell Division/Reproduction

Why?  Cells divide for many reasons:  In order to stay small Diffusion occurs at a faster, more efficient rate in smaller cells. Why would diffusion rate matter in cells? Remember what materials need to enter and exit the cell.  DNA limits their size DNA can only control cells up to a certain size.  Repair/replace old or damaged cells.  Growth and Development We start out as one cell, mitosis allows that 1 cell to turn into billions of cells.

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 Prokaryotic Cells

Cell Cycles  Contain a nucleus and organelles.  Repeating sequence of growth and division  Occurs in two cycles for two purposes  Mitosis  Occurs in somatic (ordinary body cells) for growth and repair  Creates 2 identical cells  Meiosis  Occurs in germ cells (ovaries and testes) to make gametes (sex cells).  Creates 4 similar cells. Eukaryotic Cells

Eukaryotic Cell Cycle  3 Stages  Interphase G1: First growth phase S: Synthesis phase G2: Second growth phase  Mitosis nuclear division Prophase Metaphase Anaphase Telophase  Cytokinesis Division of cytoplasm

Centromere

Interphase  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, second check- point.

Interphase (G1, S, G2)

Terms to know: (Start a VOCAB page)  Chromosome  Single piece of coiled DNA  Diploid  A cell that contains a set of chromosomes from mom and dad. (46 in Humans)  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 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 DNA related termsStructural Terms

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

Mitosis Step1: Prophase  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

Mitosis Step2: Metaphase  Chromosomes line up in the middle of the cell

Mitosis Step3: Anaphase  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.

Mitosis Step4: Telophase  Last stage of Mitosis  Chromosomes at each pole uncoil and become chromatin  Nuclear envelope reforms  Spindle fibers break down

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