MITOSIS:
CELL DIVISION
Why do cells divide?
 Growth
 Repair
 Replace dead cells
What cells divide often?
 Skin
 Stomach lining
 Red Blood cells
 Embryo
 Plant roots
 Hair
 Nails
What cells rarely/never
divide?
 Nervous System
 Liver
Why do we age?
 Eventually cells stop being replaced
 “Apoptosis”
 Cell death
 “We die because out cells die.”
 William R. Clark
“C” Terms
 Chromosomes
 Long threads of genetic
material
 Found in nucleus
 Chromatid
 One side of a duplicated
chromosome
“C” Terms
 Centromere
 Structures that hold
sister chromatids
together
 NOTE
 2 sister chromatids =
1 duplicated
chromosome
“C” Terms
 Chromatin
 DNA tnagled around a histone (a protein)
 Condensed chromatin = chromosome
Huh?
C. Duplicated
chromosome
A. DNA
B.
histone
Chromatin
“C” Terms
 Centrioles
 Small protein bodies
 In cytoplasm
 Animal cells only
Cell Division in a Nutshell
 Before:
 Chromosome duplicates = 2 sister chromatids
 During:
 Sister chromatids separate
 After:
 2 “daughter” cells
 Genetically identical
Cell Cycle
 Mitotic phase
 10%
 Interphase
 90%
Interphase
 Made up of three
phases:
 G1, S, G2
 What happens?
 Things necessary to divide
Interphase
 G1 Phase
 Cell Growth
 8-10 hours
 S Phase
 DNA replication
 Chromosome replication
 6-8 hours
 G2 Phase
 More Cell Growth
 Centriole replication
 4-6 hours
Mitotic Phase
 Mitosis
 Division of nucleus (chromosomes)
 Occurs after interphase
 Cytokinesis
 Division of cytoplasm
 Creates 2 daughter cells
 Occurs at the end of mitosis
Mitosis Phases
 Interphase
 Prophase
 Prometaphase
 Metaphase
 Anaphase
 Telophase
Task
 Draw a diagram of mitosis
 Label 6 phases & give each a short
description
Interphase
 “Resting Phase”
 Cell NOT dividing
 Precedes mitosis
 Prepares cell for division
 How?
Early Prophase
 Centrioles:
 Make spindle fibres
 Move towards opposite
plates
 Chromosomes now
visible
Late Prophase
 Centrioles reach poles
 Nuclear membrane
(envelope) & nucleolus start
to disappear
Metaphase
 Spindle fibres attach to
centromeres
 Duplicate
chromosomes line up at
equator
 Guided by spindle fibers
Anaphase
 Spindle fibers retract
 Pull sister chromatids apart
 Towards opposite polls
Telophase
 Chromatin reappears
 Nuclear membrane &
nucleolus reappear
 Cytokinesis occurs
 Result
 Two daughter cells
What phases do you see?
A
C
B
D
Cytokinesis
 Why would it occur differently in animal and
plant cells?
 Plant cells have a rigid cell wall!
Cytokinesis
Animal Cells
 Cell membrane pinches
inward
 Creates cleavagefurrow
 Think:
 Pull a string around a balloon
Plant Cells
 Cell Plate forms between
two new nuclei
 Becomes cell wall
Cytokinesis
Cytokinesis
Plant vs. Animal – Another
Difference?
 Centrioles not present in plant cells
 What makes spindle fibers in plant
cells?
 Form from cytoskeleton
Concept Map