Mitotic Cell Division - Exercise 7
Objectives
-Know the stages of the cell cycle.
-Know why mitosis is important.
-Know what types of cells do mitotic division.
-Distinguish differences between an animal and a
plant cell during mitotic division.
-Identify the different stages of mitosis under the
microscope and in models.
NOTE: YOU DO NOT NEED TO IDENTIFY CELLS IN A POLAR VIEW.
Where one chromosomes is double stranded
helices replicates so that we now have 2 helices
joined by region called center mere or
kinetochore and each of these are now called
twin chromatid or sister chromatid because
one DNA double helix replicated itself.
0.5 µm
Chromosomes
Chromosome arm
Centromere
DNA molecules
Chromosome
duplication
(including DNA
synthesis)
Sister
chromatids
Separation of
sister chromatids
Centromere
Sister chromatids
MITOSIS is a growth mechanism providing for the
production of clone daughter somatic cells and is
partially responsible for the processes of
embryonic development, growth, and healing.
Objective to create two nuclei (cells). Mitosis is to
duplicate a set of chromosomes in a parent cell to
two daughter nuclei. All cells have identical
genome because raise from one fertilize ovule in a
process called mitosis.
-Duplication of cells (46 chromosomes)
-Produces somatic cells
AUTOSOMES
• Autosomes these are the non sex determining
chromosomes. These are your cells that are involved in
mitotic division, such as, liver, skin, bone cells.
• Humans- have a total of 46 chromosomes. Twenty two pairs
of autosomes and one pair of sex chromosomes.
• Cell division in eukaryotes typically involves the distribution
of duplication sets of chromosomes in a parent cell to two
daughter nuclei (Mitosis or karyokinesis) and the division of
the cytoplasmic contents of a parent cell into two daughter
cells (cytokinesis). Cell division is only one stage (the last
(4th) stage – M) of the cell cycle.
• Mitosis is when nuclear material divides (Division of
nucleus) and cytokinesis is when cytoplasm divides.
Interphase
• G1: First growth event. The newly formed cell actively produces RNA and
protein as it grows – cell growth.
• G0: Period of no growth and it occurs prior to S phase, if it is going to
happen.
• S-phase: Cell stops producing RNA and switches to DNA replication.
Chromosomes are duplicated during the S-phase of the cell cycle. Think of
S as Synthesis of DNA.
• G2: Once the DNA has been duplicated, the cell enters another round of
RNA and protein synthesis and growth – more cell growth.
• When cells are in G1, S, and G2, they are often said to be in “interphase” –
which literally means, between mitotic division.
• Finally the cell will divide, and this stage is called M phase. Chromosomes
are too thin to see in the interphase stage under the microscope.
THE CELL CYCLE
• G1 phase- growth phase where cell makes components for DNA
synthesis.
• S phase-DNA synthesis, chromosomes replicate. DNA replicates
(synthesis)
• G2 phase-growth phase where cell makes components for DNA
synthesis.
• G0 phase-non-dividing cells. Neurons stay in this state.
• INTERPHASE-time between cell divisions-everything that is not
mitosis.
• Mitosis (M-phase)- cell divides:
– Prophase
– Metaphase
– Anaphase
– Telophase & Cytokinesis
Interphase is usually about 90%, and mitosis is the remaining
10% of the cell cycle.
MITOSIS
• A single (2n,diploid) cell divides to form two
genetically identical (2n,diploid) daughter cells.
• 4 stages: Prophase, Metaphase, Anaphase,
&Telophase (Cytokinesis)
Plant cell division
• It is necessary to obtain tissues that contain cells that are actively
dividing. One such tissue is the root tip.
• Note: The viewpoint your looking at cells is called a lateral view.
• Each cell can be considered to be a single frame of a motion picture.
Also know the parts of the cells when dividing.
• Onion root tip (Allium cepa). Most of the cells you see will not be in
the M stage of the cell cycle. That is, most cells will be in interphase.
Animal Cell Division
Mitosis is animal cells in most readily seen in early embryonic stages.
The blastula stage of an embryo is more or less a spherical ball of cells,
and cell division occurs in every imaginable plane of the embryo.
Whitefish blastula.
NOTE!!!
• A professor could ask you what are the
different stages of mitosis? In that case, you
would write down prophase, metaphase,
anaphase, and telophase.
• A professor could ask you the different stages
of the cell cycle? In that case, you would
include interphase (G1, S, G2), and mitosis
(P,M,A,T).
Question
How can you tell whether
you’re looking at a plant
cell or an animal cell?
THE CELL CYCLE
Growth period: production
of proteins and cytoplasmic
organelles
INTERPHASE
• The only significant genetic event occurring here
is the replication of DNA (all the chromosomes
duplicate).
• In interphase the chromosomes are not visible.
They exist in thread-like strands known as
CHROMATIN
• Cell is not diving. Very prominent nucleus (no
chromosomes) cell makes protein and lots of
RNA.
Interphase
These cells have obvious nuclear membranes and the
nuclear material is still dispersed as chromatin.
PROPHASE CELLS
When mitosis begins, several changes occur in the cell. The chromosomal material (called chromatin) in the
nucleus starts to condense, and eventually reaches thickness that makes them visible under the light
microscope.
As prophase proceeds, the chromosomes continue to get shorter and thicker, and eventually begin to move
toward the equator of the cell, midway between the poles. Prophase is typically the longest phase of
mitosis.
interphase
prophase
-Chromosomes condense and become visible
-Nuclear membrane breaks down
-Nucleoli vanish
Prophase
Several cells are seen in various stages of prophase. Note the
presence/absence of a nuclear membrane and the spindle apparatus,
and the chromatin beginning to condense as visible chromosomes.
METAPHASE CELL
Chromosomes are short and thick will reach the center of the cell called the equatorial plane or metaphase plate.
The duplicated chromosomes are separated from one another, except at one point called the kinetochore
(centromere). When the duplicate chromosomes are in this attached condition, as they have been since they
were duplicated, each strand is called a sister chromatid.
At the conclusion of metaphase each centromere, holding two identical sister chromatids, is attached to two
spindle fibers, one from each pole.
-chromsomes line up on the center line of the cell
-centromeres duplicate
-spindle fibers attach to centromeres
Metaphase
The two cells in the center are in metaphase. In each, notice the
chromosomes are aligned at the cell’s equator and the well
formed spindle apparatus.
ANAPHASE CELL
Anaphase begins with the separation of sister chromatids of each duplicated chromosome. Each chromatid
is moved by motor molecules that ratchet along the spindle fibers toward the polar ends.
The original chromosome and its exact duplicate are pulled to opposite poles of the cell. This happens for
each different chromosome that the cell possesses; thus, each pole will eventually obtain exactly the same
set of chromosomes that were in the original nucleus. In anaphase the chromatids are separated.
• -Sister chromatids move to opposite poles of the cell
• -Spindle fibers pull the chromosomes apart by the
centromeres
Early Anaphase
The spindle apparatus has begun to separate the
chromosomes in the upper cell. The cell near the bottom of the
field as in metaphase.
Late Anaphase
• The chromosomes are close to the centrosomes, which
means they have moved apart just about as far as they
will go.
TELOPHASE CELL
Plant cell
Animal cell
The events of telophase are essentially the reverse of the those of prophase.
At the end of this, there are two nuclei, each having identical sets of
chromosomes.
TELOPHASE
• Sister chromatids reach the opposite poles
and begin returning to the interphase state.
• Nuclear membrane and nucleoli reform.
• Spindle fibers disperse.
• Cytokinesis occurs.
• A cell plate (plants) or a cleavage furrow
(animals) forms.
Cytokinesis : division of cytoplasm
• Animal cells : cleavage
– Cleavage furrow
• Division begin as a shallow groove in the cell surface near the
metaphase plate
– Contractile ring (on the cytoplasmic side of the furrow)
• Composes of actin microfilaments and the protein myosin
– Cleavage furrow deepens until the parent cell is pinched in
two
• Plant cells : cell plate formation
– Vesicles from the Golgi collect at the middle of the cell
producing a cell plate
– Cell wall material carried in the vesicles is deposited on the
plate as it grows, until it fuses with the membrane along the
perimeter of the cell
Late Telophase and Cytokinesis
The cleavage furrow has nearly divided the two cells, so cytokinesis is
almost complete. Telophase will continue with the chromosomes
dispersing as chromatin and the nuclear envelope reforming.
Polar view
The cell in the center doesn’t fit any of the description
because it is begin viewed from one end (pole) rather than from
above.
Cleavage furrow
The cleavage furrow (CF) has begun to form.
Cytokinesis in animal and plant cells
Cell Division
• Reproduction
A singlecelled
eukaryote
(amoeba)
reproduces
– Equal distribution of genetic
material to two daughter cells
• Growth
– Sexually reproducing
organisms develop from a
single cell (zygote)
Sand dollar
embryo after
the egg
divided to
form 2 cells
• Repair
– Replace cells that die from
normal wear and tear or
accidents
Dividing bone
marrow cells
produce new
blood cells
Interphase
Early Prophase
Late Prophase
Metaphase
Early Anaphase
Late Anaphase
Telophase - Cytokinesis
Interphase 2
Animal Vs. Plant Cells
-What are some differences between an animal cell and a
plant cell?
Animal Vs. Plant Cells
-What are some differences between an animal cell and a plant cell?
Plants have a cell wall, after telophase plant cells divide by forming a cell
plate, and animal cells form a cleavage furrow. Plant cells are rectangular,
and animal cells are more circular.
Mitosis - Review
Page 8 – Lab Book
• 1. Why are the onion root tip and the whitefish blastula useful tissues
for the study of cell division?
• 2. Distinguish between mitosis and cytokinesis.
• 3. If a cell has 16 chromosomes when it is in G1, how many
chromosomes will there be in each daughter cell following a mitotic cell
division?
• 4. What are the genetic consequences of mitotic cell division for the
resulting daughter cells?
• 6. How do plant and animal cells differ in the execution of cytokinesis?
Why don’t plant cells undergo cytokinesis in the same manner as animal
cells?
Page 8 – Lab Book
• 1. Why are the onion root tip and the whitefish blastula useful tissues for the study
of cell division? These two tissues were actively dividing, so we (classmates)
could find cells under going mitosis at different phases.
• 2. Distinguish between mitosis and cytokinesis. Mitosis is the division of the
nucleus (nuclear division) produces 2 identical nuclei. Cytokinesis is the division
of the cytoplasm – produces 2 cells.
• 3. If a cell has 16 chromosomes when it is in G1, how many chromosomes will
there be in each daughter cell following a mitotic cell division? 16
• 4. What are the genetic consequences of mitotic cell division for the resulting
daughter cells? Every cell is genetically identical to each other. Produces 2
identical nuclei, each with the same number and types of chromsomes as the
parent cell.
• 6. How do plant and animal cells differ in the execution of cytokinesis? Why don’t
plant cells undergo cytokinesis in the same manner as animal cells?
Figure 12.8 Cytokinesis in animal and plant cells
Page 9 – Lab Book
• 7. List several important values or attributes that
mitotic cell division provides to multicellular life. In
other words, in what ways is mitotic cell division
useful for life?
• 8. List the 4 stages of the cell cycle and describe the
primary cellular activity in each stage.
Cell Division
• Reproduction
A singlecelled
eukaryote
(amoeba)
reproduces
– Equal distribution of genetic
material to two daughter cells
• Growth
– Sexually reproducing
organisms develop from a
single cell (zygote)
Sand dollar
embryo after
the egg
divided to
form 2 cells
• Repair
– Replace cells that die from
normal wear and tear or
accidents
Dividing bone
marrow cells
produce new
blood cells
Questions
1. How many daughter cells are produced by mitosis?
2. How does the number of chromosomes in each
daughter cell compare with the number of
chromosomes in the original parent cell after mitosis?
3. When are chromosomes replicated?
4. During cytokinesis plant cells form a _________
while animal cells form a ____________.
Questions
1. How many daughter cells are produced by mitosis? 2
2. How does the number of chromosomes in each
daughter cell compare with the number of chromosomes
in the original parent cell after mitosis? Same number
and type of chromosomes.
3. When are chromosomes replicated? Interphase,
specifically S-phase
4. During cytokinesis plant cells form a cell plate while
animal cells form a cleavage furrow.