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Cell Division and Mitosis

Cell division is necessary for maintenance, growth, and reproduction

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Cell Cycle

  • The cell cycle is like the life cycle of the cell.
  • It is a different length in each type of cell. Some plant cells have a cell cycle of 19 hours and some animal cells have a cell cycle of about 16 hours.
  • The cell cycle has 3 parts: Interphase Mitosis, and cytoplasm division

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Interphase

  • Interphase is the longest part of the cell cycle
  • Interphase is a period of growth and development. Cells that are not dividing (like nerve cells) stay in interphase.
  • If an actively dividing cell, the DNA is copied during interphase.

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DNA, Chromosomes, Chromatids

  • DNA is the molecule that contains genes and genetic information.
  • DNA is organized into chromosomes.
  • During interphase, chromosomes are copied.
  • When the cell is ready to divide, the chromosomes coil tightly into two thickened identical strands called chromatids.
  • Identical chromatids are held together at the centromere.

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In humans...

  • We have 23 pairs of chromosomes
  • Every single cell in your body has the same 23 pairs of chromosomes

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  • Your cells are different because they use different parts of the DNA in the chromosomes

  • Sex cells or GAMETES are the only cells that do not have 23 pairs of chromosomes, they just have 23 chromosomes, or half the number of chromosomes of body or somatic cells
    • This is accomplished through MEIOSIS, which we will learn about later

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Mitosis

  • Mitosis follows interphase and is the first step in cell division.
  • Mitosis is the process in which the cell’s nucleus divides to form two identical nuclei.
  • There are four phases of

nuclear division.

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Prophase

  • Chromatid pairs are visible
  • Nuclear membrane breaks apart
  • Two centrioles (in animal cells) move to opposite sides of cell. Centriole is part of the centrosome, which makes microtubules.
  • Spindle fibers form between centrioles.

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Metaphase

  • meta means middle!
  • chromatid pairs line up along the MIDDLE of the cell
  • Spindle fibers from either side of the cell attach to the centromere

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Anaphase

  • Centomeres divide
  • Spindle fibers shorten and pull chromatids away from their sister chromatids
  • As unduplicated chromatids move to opposite side of the cell, they are now called chromosomes

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Telophase

  • Spindle fibers start to disapear
  • Chromosomes start to uncoil
  • Two new nuclei form

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Cytokinesis

  • Division of the cytoplasm
  • Two new cells are formed, each with half of the cytoplasm of the original cell
  • Both of the new cells start in interphase again

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Cytokinesis in Plant Cells

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Remember!!!

  1. Mitosis is the division of a cell’s NUCLEUS
  2. Mitosis produces two nuclei that are identical to each other and to the original nucleus.
  3. Cytokinesis is the division of a cell’s CYTOPLASM

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Asexual Reproduction

  • Single celled Eukaryotes and other organisms that reproduce asexually, use mitosis and cytokinesis to reproduce
  • Prokaryotes (Bacteria) do not have a nucleus, so they cannot undergo mitosis, instead BINARY FISSION
  • In asexual reproduction, all new organisms are indentical to each other and to the original organism