PBIO 100 LECTURE NOTES

Undergraduate Program in Plant Biology, University of Maryland

LECTURE 6- MITOSIS - CELL DIVISION

I. Growth of cells

• A. Three aspects
  • 1. Cell reproduction (cell division) animals get layer of cells
    2. Cell enlargement - plants get larger
    3. Cell differentiation
• B. Site of cell growth in plants - meristems

II. Two parts to cell division

• A. Mitosis (animated) - [for a Quick Time^® movie of mitosis in animal cells visit this site at the University of Texas and follow the stages of the process] - division of nucleus (each daughter cell has complete set of blueprints)
  B. Cytokinesis - division of cytoplasm

III. Phases of mitosis: To see stages of mitosis, go down the page. Be sure to compare plant vs. animal cells - See also mitotic cell divisions in onion showing chromosome structure

• A. Interphase (scroll down to see pictures)
  • 1. Not part of mitosis; a preparatory stage
    2. Respiration, protein synthesis, growth occurs
    3. Genetic material is duplicated (DNA replicates) itself
    4. Cells usually small with no large vacuoles
• B. Prophase
  • 1. Nuclear envelope disappears
    2. Nucleolus disappears
    3. Chromatin condenses (shortens and thickens) to become chromosomes
    4. Later, spindle starts to form (spindle composed of microtubules - like muscles)
• C. Metaphase
  • 1. Chromosomes line up on equator
    2. Each centromere attached to spindle fiber
    3. Very end of metaphase - centromeres divide
• D. Anaphase
  • 1. Sister chromatids are pulled to opposite end of cell by contraction of spindle fibers
    2. Each chromatid is now considered one chromosome
• E. Telophase (reverse of prophase)
  • 1. Nuclear envelops reforms (2)
    2. Chromosomes lengthen and become indistinct (chromatin)
    3. Nucleolus reappears

IV. Cytokinesis begins

• A. Usually follows mitosis
  • 1. Plants
    • a) Cell plate forms in middle of cell from aggregating vesicles from Golgi - 2 plasma membranes
      b) Later, cell wall material is laid down from Golgi
  • 2. Animals

V. Key thing to remember is the purpose of mitosis: the exact duplication of cellular "master plan" in nucleus

• A. Constant number of chromosomes for each species
  • 1. Humans = 46
    2. A sunflower = 4
    3. A fern = 1250
    4. Most plants 20-40 chromosomes
• B. Daughter cells diploid (2n), not haploid (n)
  C. Importance of chromosome number and mitosis
  • 1. Following cell division, each daughter cell must contain the same number of chromosomes as the parent cell
    2. Since genes are located on the chromosomes, each new cell must contain the same number of genes as the parent cell

VI. OPTIONAL: Timing of mitotic cycle in pea root tip

     Stage               Time        %

     Interphase          17 hours  90.3%

     Prophase             1.3       6.9

     Metaphase            0.24      1.3

     Anaphase             0.07      0.4

     Telophase            0.22      1.2

         TOTAL           18.83 hours

Link to other sites

A beginner's guide to molecular biology: A scary title but really filled with wonderful stuff on cells!
Mitosis in plant cells-Pictures and descriptions from Dr. Wolniack's laboratory
Cell Division: A review
Mitosis: Compare plant and animal mitosis
Cell Division and Mitosis

Last revised: Feb 5, 1999, Straney