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Cell Division in Eukaryotes
• As you are sitting in class now, your
cells are growing, dividing and dying.
Cuts and bruises are healing
Muscle cells are
get larger when
you exercise.
RBC’s are being
produced in your
bones at a rate of
10-15 million per sec.
Worn out cells in the palm of your hand are being replaced.
Cell Division
How do you grow?
The number of cells in your body is increasing!!
How Do Cells Increase In
Number?
• In your body, all of your cells, except your
sex cells, divide by a process called mitosis.
• In mitosis, a parent cell divides to form two
identical daughter cells.
• The daughter cells have the same contents
of the parent’s nucleus.
Cell Cycle
• Most of a eukaryotic cell’s life is
spent in a phase called interphase.
• Interphase consists of three stages: G1, S,
and G2
– G1: a time of growth and maintenance
– S: DNA is replicated: this commits the
cell to divide
– G2: more growth as the cell prepares
for division
Cell Cycle
• Mitosis: division of the
nucleus:
– Four phases: prophase,
metaphase, anaphase and
telephase.
• Cytokinesis: division
of the cytoplasm
• After the cell divides
into 2 identical daughter
cells, the cycle starts
over again.
http://www.cellsalive.com/cell_cycle.htm
Cell Cycle
Interphase
• Chromatin coils up into chromosomes
• A copy of each chromosome in the nucleus is
produced
• These duplicated chromosomes are held
together by a centromere.
• Cells that no longer divide are always in
interphase.
Chromatin / Chromosomes
Interphase
Mitosis in Animal Cells
• A form of asexual
reproduction
• The nucleus of a cell
divides, producing 2
nuclei that are
identical to each
other
• Has 4 phases:
prophase, metaphase,
anaphase, telophase
Prophase
• Duplicated chromosomes become fully visible
• Organelles called centrioles move to opposite ends of
the cell
• The nucleolus and nuclear membrane disintegrate
• Threadlike spindles stretch across the cell between
the centrioles
Prophase
Metaphase
• Duplicated chromosomes line up across the
center, or equator, of the cell.
• Each centromere attaches to 2 spindle fibers
Metaphase
Anaphase
• Each centromere splits and the identical
chromosomes separate and move towards
opposite ends of the cell.
Anaphase
Telophase
• Spindle fibers disappear
• Chromosomes uncoil and are harder to see
• A nuclear membrane forms around each mass
of chromosomes
• A new nucleolus forms in each new nucleus
Telophase
Cytokinesis
• The cytoplasm and its contents divide
into 2 individual daughter cells.
• Each daughter contains a nucleus and
identical chromosomes.
Animal Cytokenesis
• Cytokenesis differs
significantly between
Animal & Plant cells.
• With animals, the
membranes pinch
together to form a
Cleavage Furrow,
which eventually fuses
to form two daughter
cells
Plant Cytokenesis
• With Plants, a cell wall must be formed between the 2
daughter cells.
• Vessicles containing Cellulose form and fuse between
the tow daughter cells, eventually forming a complete
cell wall.
Overview of Mitosis
Virtual Lab
• http://ridge.icu.ac.jp/gen-ed/celldivision.html
• Cell Reproduction
• http://bio.rutgers.edu/~gb101/virtuallabs_10
1.html
Mitosis in Plant Cells
• What’s Different?
• Plant Cells do not have centrioles
• A cell plate forms between 2 new nuclei
• New cell walls form along the cell plate, and
new cell membranes form inside the cell walls.
Plant Mitosis
"And do you, Michelle, take Andrew
until mitosis do you part?"
Regulating the Cell
• Not all cells grow and
divide at the same rate.
– most muscle and nerve
cells rarely divide
– skin cells and cells in
the bone marrow that
make blood divide
every few hours
Cyclins
• group of closely related proteins that
regulates the cell cycle in a eukaryotic cell.
• their concentration varies in a cyclical
fashion during the cell cycle
– they are produced or degraded as needed in
order to drive the cell through the different
stages of the cell cycle.