Mitosis Overview
Objectives
• Name and describe the two types of
reproduction.
• Explain what happens during the cell
cycle.
• Explain what happens in the stages of
mitosis.
• Discuss how mitotic cell division in
unicellular and multicellular organisms
are controlled.
Terms to know:
-mitosis
-interphase
-metaphase
-telophase
-asexual reproduction
-sexual reproduction
-budding
-gametes
-cytokinesis
-prophase
-anaphase
-cell cycle
-chromosomes
-binary fission
-spores
-chromatin
Why must cells divide:
Cells must divide in order for an organism
to be able to:
• Grow
• Maintain and repair body tissues
• Reproduce
Function of mitotic cell division
• Mitosis is important for the growth,
maintenance, repair, reproduction of
eukaryotic body cells.
• Kidney, liver, skin, heart, pancreas cells
etc. all reproduce by mitotic cell divisions.
• Mitosis results in 2 daughter cells that
have the exact same DNA as the mother
cells.
Two major types of reproduction
1. Asexual reproduction: Only 1 parent
organism reproduces by itself, no sex
cells are involved. Offspring are
genetically identical to parent.
2. Sexual reproduction: Two parent
organisms reproduce to form a new
organism. Gametes or sex cells (sperm
and egg) are involved. Offspring are
contains genes from both parents.
Two types of reproduction:
• Asexual reproduction occurs in single
celled organisms, some plants, and some
animals.
• Sexual reproduction occurs in most
animals and plants.
Cell Division
• Before it becomes too large, a
growing cell must divide forming
two daughter cells.
• The process by which a cell divides
into two new daughter cells is called
cell division.
Cell Division
• Before cell division occurs, the cell
replicates, or copies, all of its DNA.
• This replication of DNA solves the
problem of information storage because
each new daughter cell gets one
complete set of genetic information.
• Thus, each daughter cell now contains
its own genetic “library”.
The cell cycle and mitosis
• During the cell cycle, a cell grows,
prepares for division, and divides to
form two daughter cells each of which
then begins the cycle again.
• Mitosis: A process of the cell cycle
that occurs when a cell with a distinct
nucleus divides to form two daughter
cells.
5 Phases of the cell cycle
1. The cell grows and develops (G1)
2. The genetic material is replicated
inside the parent cell (S)
3. The cell continues to grow and develop
(G2)
4. The nucleus divides in two separating
the genetic material into two equal
parts (mitosis)
5. The cytoplasm divides forming two new
daughter cells (cytokinesis)
Cell cycle and mitosis
Questions:
1. What does the nucleus contain and
why must it divide?
2. What kinds of cells can undergo
mitosis?
(eukaryotic or prokaryotic)
Mitosis and changes in the nucleus
• DNA is the genetic information
needed to make important cell
structures. It also determines how
the organism will look, behave, and
function.
• Before a cell divides, the DNA must
be replicated so that each new
daughter cell has a copy of the
information.
Mitosis and changes in the nucleus
• Before the cell divides, the DNA in
the nucleus appears as loose fibers
called chromatin.
• Before mitosis begins, the DNA
must be replicated.
• As the cell enters mitosis, the
chromatin coils up into structure
called chromosomes.
Mitosis and changes in the nucleus
• Imagine: Each strand of DNA within
each of your cells is about 6 feet
long. The DNA becomes so tightly
coiled into the chromosomes that it
can actually fit into a microscopic
cell!!
• Humans have 46 chromosomes in each
of our body cells.
What exactly is a chromosome?
Chromosomes are
composed of tightly
coiled DNA and
proteins called
histones, which
allow the DNA to
coil into these
compact structures.
Chromosomes
contain genes
which code for
various traits.
Chromatid
Mitosis and changes in the nucleus
• During cell division, before mitosis,
it is the chromosomes that
duplicate.
• Why must the chromosomes
duplicate before mitosis?
Interphase and Mitosis
• When a cell is not dividing, it is in
interphase.
• During interphase the cell:
– Grows in size
– Replicates its chromosomes (they
double in number)
– Metabolic activity is at its highest
Mitosis –Division of the nucleus
• Mitosis involve 4 phases.
1. Prophase:
2. Metaphase:
3. Anaphase:
4. Telophase:
Plainedge Made A Touchdown
Prophase
• The chromatin
thickens and
coils into
chromosomes
• The nuclear
membrane
disappears
• Mitotic spindle
fibers form
from centrioles
• Spindle fibers
align the
chromosomes
along the middle of
the cell nucleus.
This line is called
the metaphase
plate.
• This organization
helps to ensure
that in the next
phase, when the
chromosomes are
separated, each
new nucleus will
receive one copy of
each chromosome.
Metaphase
Anaphase
• The paired
chromosomes
separate at the
kinetochores and
move to opposite
sides of the cell.
• Kinetochore: part of
chromosomes where
spindle fiber attaches
• Motion results from a
combination of
kinetochore
movement along the
spindle microtubules
Kinetochore and Spindle Microtubules
Telophase
• Chromatids arrive at
opposite poles of cell, and
new membranes form
around the daughter
nuclei.
• The chromosomes
disperse and are no
longer visible under the
light microscope.
• The spindle fibers
disperse, and cytokinesis
or the partitioning of the
cell may also begin during
this stage.
Cytokinesis
• In animal cells,
cytokinesis results
when a fiber ring
composed of a protein
called actin around
the center of the cell
contracts pinching the
cell into two daughter
cells, each with one
nucleus.
• In plant cells, the rigid
wall requires that a
cell plate be
synthesized between
the two daughter cells.
Whitefish Mitosis
interphase
anaphase
prophase
metaphase
telophase
What Phase is this?
• Prophase
• Nuclear membrane is
gone.
• DNA condensed into
chromosomes
How about this?
• Anaphase
• Chromosomes are
being pulled apart to
opposite ends of the
cell.
What Phase is this?
• Telophase
• Nuclear membrane
has reappeared
• DNA is now in
chromatin form.
• Cell membrane
pinches cell into 2
new daughter cells.
What Phase is this?
• Metaphase
• Chromosomes are
lined up in the center
of the cell.
• Spindle fiber network
is visible
What Phase is this?
• Interphase
• Nuclear membrane is
visible
• DNA in form of
chromatin.
Related Websites
• http://www.cellsalive.com/mitosis.htm
• http://www.biology.arizona.edu/cell_bio/tutorials/cell_cy
cle/cells3.html
• http://www.sci.sdsu.edu/multimedia/mitosis/
• http://biologyinmotion.com/cell_division/
• http://www.life.umd.edu/CBMG/faculty/wolniak/wolniak
mitosis.html
• http://www.bio.unc.edu/faculty/salmon/lab/mitosis/mitosi
s.html