Why do cells need to divide?
How do cells divide? What needs to happen to
make an exact copy of this cell?
• Does an organism grow because its cells get larger or
because it increases the number of cells?
• What limits the size that a cell can reach?
• How does the surface area change when a large cell
divides into smaller cells that have the same total
volume?
• Are cells dividing all the time?
• Do all cells divide at the same rate?
• What must duplicate/replicate before a cell divides?
Types of Reproduction
• Asexual Reproduction
– Cloning of an individual
cell
– Produce genetically
identical offspring
– Occurs in bacteria, body
cells
• Sexual Reproduction
– Occurs when two
reproductive cells join
– Make genetically diverse
cells since the offspring
get traits from both
parents
Vocabulary
Chromatin- long strand of
DNA
Chromatid- each strand of a
duplicated chromosome
Centromere- the area where
two chromatids are
joined. Splits during
anaphase.
Kinetochore- a protein on
chromosomes where
spindle fibers attach.
Centrioles- tiny structures
in the cytoplasm of
animal cells that help
organize the spindles. (2
centrioles =centrosome)
Spindle fiber- a fanlike
microtubule structure
that helps separate the
chromatids
• Spindle- a fanlike
microtubule structure
that helps separate the
chromatids -composed
of centrioles and
spindle fibers
Cell Cycle- Interphase
• G1 – Cell Growth-increase
in size, routine functions
(longest)
• S – DNA replication-
Synthesis of new DNA/
chromosomes replicated
• G2- Preparing for Cell
Division- replication
of organelles,
microtubules and
other molecules for
cell division
• http://iknow.net/cell_div_education.html
M Phase (minutes to days)
• Mitosis
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
Pro=before
Meta=after
Ana=back
Telo= end
• Cytokinesis
– Division of the
cytoplasm and
organelles
Mitosis- phases
• Prophase
– Chromosomes become
visible (coil)
– nuclear membrane
dissolves
– Spindle forms
– Nucleolus disappears
Prophase
Metaphase
• Chromosomes line up
along the equator
• Spindle fibers connect
centromeres (of
chromatids) to opposite
poles
Anaphase
• Centromeres divide
• Chromosomes move
toward opposite poles
– Each Sr. Chromatid is
pulled toward opposite
pole
• Spindle fibers shorten
Telophase
• Reverse of Prophase
• Nuclear membrane
forms at each pole
• Chromosomes uncoil
• Spindle fibers dissolve
• Cytokinesis begins
Cytokinesis
• Cytoplasm divided in
half
• Cell membrane pinched
by a belt of protein
threads or contractile
ring
Plant vs Animal Cell Division
Animals
• Centrioles
• Pinching or cleavage of cell
membrane
Both
Equal sized offspring cells
Identical copy of original cell’s
chromosomes
Plants
• No centrioles
• Vesicles fuse forming a cell
plate
• A new cell wall forms on
either side of the cell plate
Animal and Plant Cell Division
• http://iknow.net/cell_div_education.html
•
•
•
•
Prophase- a “pro” is #1
Metaphase- “M” middle
Anaphase- Away
Telephase – Two nuclei
• http://glencoe.mcgrawhill.com/sites/dl/free/0078802849/164155/00
053413.html