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Chapter 8
Cells must divide for
 Growth
 Repair
Cells cannot just continue to
grow larger for two reasons:
 Exchanging materials
 The surface area of the cell membrane must be large
enough to support the volume of the cell.
 Otherwise, the cell struggles keeping up with the
exchange rate of food, oxygen and water across the
 Information overload
 Too many demands on the DNA to get its information
where it is needed.
Mitosis The process by which a cell divides, forming two
“daughter” cells
 These daughter cells are identical to the parent cell
Which cells ?
 Eukaryotic somatic (body) cells undergo mitosis
 Prokaryotic cells go through a process called binary
 Made up of DNA wrapped tightly around histone
 DNA + histones = chromatin fiber and looks like
“beads on a string”
 During mitosis chromatin condenses and coils to form
 Sister chromatids- Each side of a duplicated
 Centromere- Center of a chromosome, holds sister
chromatids together
Chromosome number varies for
each species
 Humans= 46
 Cat= 38
 Fruit fly= 8
The cell cycle
 Mitosis is part of the cell’s life cycle
 This cycle includes the following stages:
 Interphase
 Mitosis
 Cytokinesis
 The longest phase of the cell cycle
 The cell prepares to divide
 3 phases, or checkpoints, in Interphase
Phases of Interphase
 G1 - intense cell growth, cells contents duplicated
 S - DNA is replicated (copied)
 G2 - more growth and final preparation for cell division
 G0- cell enters this phase when something is wrong and it
either can’t or won’t divide. Ex: unstable environment,
DNA was copied incorrectly, more cells not needed at that
The Cell Cycle
After a cell goes through all the
checkpoints, it is ready to divide!
 The Mitotic phase of the cell cycle includes
 Prophase
 Metaphase
 Anaphase
 Telophase
 Nuclear envelope disappears
 Chromatin condenses
 Chromosomes are first visible
 Centrioles split and move to opposite sides of the cell
 Chromosomes line up in the middle of the cell
 Spindle fibers connect to chromosomes at the
 Metaphase = Middle
Metaphase (plant cell)
 Sister chromatids pulled apart to opposite sides
 Spindle fibers shorten
 Anaphase = Away, or Apart
 Two sets of genetic information on either side of the
 Nuclear envelope reforms around each set
 Chromosomes no longer visible (unravel into
chromatin again)
 After mitosis is complete, the cell has one thing left to
do- split! (cytokinesis)
 Splitting of the cytoplasm
 Forms two new distinct “daughter” cells
 Two cells are genetically identical
 In animals- Cell membrane “pinches off”
 In plants- Cell plate forms
 In animals: Cell membrane “pinches off”
 In plants: Cell plate forms
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