Transcript The Cycle of a Dividing Cell

Biology 1110 Laboratory
Laboratory # 9
The Cell Cycle and Mitosis
Support/Review Materials
All of the micrographs in this presentation were photographed in the MnWest
Biology laboratory unless otherwise noted.
The microscope symbol that you see indicates
power. A left mouse click on the microscope
viewing magnification. Give it a try.
a change in microscope
most often increases the
The object of the cell cycle is
to produce two “daughter”
cells from the single
“mother” cell.
DNA, the genetic material,
contains all of the
instructions to run the cell.
The necessity of DNA
duplication during
interphase should be
obvious.
Mitosis takes up about 10%
of a typical cell cycle.
Through the phases of
mitosis the cell’s nucleus
divides to form the two
“daughter” nuclei.
With the two “daughter “
nuclei formed, the cell is
ready to separate into two
separate cells.
The mitotic phases
accomplish the nuclear
division. They are:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
We will study interpase and
the mitotic phases in both
animal and plant dividing
cells.
The two low power micrographs below are whitefish
blastulas. A blastula is an early stage an embryo consisting of
many cells.
Growth of the embryo involves rapid cell cycles that can be
readily studied microscopically.
Cell Cycle
Whitefish Blastula
These two low power micrographs
contain numerous cells in the
interphase (see )of the cell cycle.
During the interphase the nuclear
membrane is present and the
nuclear content consists of the
granular chromatin.
The chromatin contains the DNA
(genetic material) that must be
duplicated.
Let’s take a closer look
InterPhase
The nucleus is intact,
surrounded by a nuclear
membrane.
The granular chromatin is
clearly visible.
It is this chromatin that will
give rise to the
chromosomes as we move
into the mitosis.
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Remember that the purpose of the mitosis is to
produce the two “daughter” nuclei.
The division of the nucleus is accomplished
through the four mitotic phases. They are:

1. Prophase

2. Metaphase
3. Anaphase
4. Telophase
The typical dividing cell
spends about 90% of its time
in a period called
interphase.
During the interphase, the
cell is growing, carrying out
its normal metabolic
functions, duplicating its
DNA, and getting ready for
the next division.
Mitosis – Prophase Events
The major events of the prophase
include the following:
- the nuclear membrane disintegrates.
- the chromatin condenses (wraps
up) forming the chromosomes.
- the mitotic spindle begins to form.
Let’s take a closer look



The high power
micrograph demonstrates
two cells in prophase.
The chromatin is
condensing, giving rise to
the rod-like chromosomes.
The chromosomes are
deeply stained and clearly
visible.
Metaphase of Mitosis
After the prophase the cell moves into
the metaphase.
In the metaphase the chromosomes
lineup at the midplane of the cell.
Metaphase
The chromosomes are contained
within the mitotic spindle. The fibers
of the mitotic spindle are clearly
evident in both
micrographs.
Let’s take a closer look


On high power we
clearly see the lined
up chromosomes
contained within the
mitotic spindle.
The spindle fiber
attach to the
chromosomes
Mitotic spindle
In this metaphase diagram we can
see the chromosomes lined up
within the mitotic spindle.
We also note that the a spindle
fiber attaches to each chromosome
from each direction.
Note that each chromosome
consists of two identical
chromatids (“sister” chromatids).
From this we understand that the
cell contains two full sets of genetic
instructions.
Anaphase of Mitosis
As the cell enters the anaphase of
mitosis, the two chromatids of each
chromosomes begin to separate.
The spindle fibers begin to retract
and pull the chromatids
(chromosomes) towards each pole of
the cell.
The separation of anaphase separates
the two identical sets of DNA; the
two identical sets of instructions.
Anaphase
The anaphase diagram
clearly shows the
separation of chromatids.
The spindle fibers pull the
two sets of genetic
instruction apart.
The formation of the two
“daughter” nuclei is well
underway.
Direction of movement
Telophase of Mitosis
Telophase is the last phase of
mitosis.
The mitotic spindle has finished
its job and disintegrates.
The two daughter nuclei are
forming.
The cell will separate into the
two “daughter” cells.
Go to high power
Both of these animal cells have taken on the shape of the number 8.
Note the cleavage furrow (constriction) at the pointer. This
constriction will continue until the two “daughter” cells separate.
The illustration demonstrates the
major events of the telophase.
The mitotic spindle disintegrates.
The two “daughter” nuclei are
forming.
The “mother” cell is dividing to
produce the two “daughter” cells.
This division is called the
cytokinesis.
“daughter” nuclei forming
spindle
You may remember from a
previous lab that plant meristems
are tissues where rapid cell division
supports primary growth.
Meristematic tissue is found in
stem tips and root tips.
We are going to study dividing
cells in the Allium (onion) root tip
Let’s take a high power
look at this root tip.
Interphase in a Plant Cell
Take a look at this interphase
cell.
The black arrow is pointing
to the plant cell wall.
The red arrow is pointing at
the nucleus.
Within the membraneenclosed nucleus we see the
grainy chromatin material.
You can see the chromatin
starting to condense to form
chromosomes in these early
prophase cells.
Can you find a third prophase
cell in the micrograph?
There are also many interphase
cells for you to look at.
You will see quite a similarity to
the events of the animal cell cycle.
Later in prophase the rodlike forming chromosomes
become much more
apparent.
Late Prophase
Later in the prophase, the
chromatin codensation
,forming the rod-like
chromosomes is well
demonstrated.
Forming Chromosomes
Like in the animal cell, the metaphase chromosomes line up
at the midplane.
Remember that each chromosomes contains two sets of
genetic instructions.
The separation of the two chromosomes groups (two sets of
instructions)can be clearly seen in the identified cells.
The formation of the two “daughter “ nuclei is well under
way.
Cytokinesis (division of the cell) is occurring in the identified
plant cells.
The rigid plant cell wall prevents the type of division we saw in
animal cells.
The “daughter” cells are formed
as first a cell plate and then new
cell wall forms between the
“daughter” nuclei.
The cycle is complete.
Daughter Nuclei
Cell Plate
You should be able to find all studied stages and phases in
the micrographs below.
Interphase.
Note the distinct
nucleus.
The granular chromatin
is present in the nucleus.
Early Prophase.
The chromosomes are
starting to form from the
chromatin.
Later Prophase.
Chromosomes almost fully
formed.
Mitotic spindle is developing
The fully formed
metaphase chromosomes
line up at the midplane of
the spindle.
Late metaphase; early
anaphase.
The separation of the
chromosome groups is
starting.
This anaphase model
shows clear separation of
the two chromosome
groups.
“Daughter” nuclei forming
Cytokinesis (cell division)
nearly complete
Spindle
disintegrates
Two “daughter” cells entering the
next interphase
Try it again