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Cell Division
Pages 55-62 “C” in book
Cells go through a cycle. During this cycle, the
cells make a copy of their DNA and a new cell is
created. This process is what allows a huge
pumpkin to grow from a tiny seed and become
larger and larger! The cells duplicate over and
over and over again and so the pumpkin gets
larger.
Be sure you only take notes on the
bold and underlined sections.
• You will have an assignment at the end of the
power point presentation and you will get
your notes and pictures from your book also.
The new cells are called daughter
cells.
• This cell cycle has a regular sequence of
growth and division. Each of the daughter
cells will begin the cell cycle again.
• There are three main stages: interphase,
mitosis, and cytokinesis.
Think of it as the phases or stages you
go through in your life:
• 1. Infant
3. Adolescence
2.Toddler
4. Adult
5. Old age
What does the cell cycle look like?
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See page 58 & 59 “C”
in your textbook.
1 & 2 Interphase
3. Prophase
4. Metaphase
5. Anaphase
6. Telophase
7. Cytokinesis
Stage 1-Interphase
• 1st stage of cell cycle. This is the period before cell
division. Some call it “resting stage” ------it is not!
• What happens during interphase? The cell grows,
makes a copy of its DNA, and prepares to divide
into two cells. There are also two structures called
centrioles that are also copied.
Stage 2 is Mitosis
• Mitosis is actually divided into smaller stages
that are quite easy to see. The chromosomes are
in different positions for each of the stages in
mitosis. The stages within mitosis are:
• A. Prophase
• B. Metaphase
• C. Anaphase
• D. Telophase.
• Let’s look at each one separately.
Prophase
• The chromatin (nucleic acid – DNA & RNA) in
the nucleus condenses and forms
chromosomes.
What else occurs during prophase?
• The pairs of centrioles move to the opposite
sides of the nucleus and spindle fibers form a
bridge between the ends of the cell. The
nuclear envelope breaks down and then it
disappears.
Next stage = Metaphase
• During metaphase the chromosomes line up
across the center of the cell. Each
chromosome attaches to a spindle fiber at its
centromere.
• Metaphase
Next comes Anaphase
• What happens—the centromeres split. The
two chromatids separate. One chromatid is
drawn by its spindle fiber to one end of the
cell. The other moves to the opposite ends of
the cell. The cell stretches out.
Now we are at telophase
• The chromosomes begin to stretch out and
lose their rod-like appearance. A new nuclear
envelope forms around each region of
chromosomes.
Last thing to occur is Cytokinesis
• The cell membrane pinches in around the
middle of the cell. The cell splits in two. Each
daughter cell ends up with an identical set of
chromosomes and about half the organelles.
During cytokinesis remember:
• The cytoplasm divides, the organelles are
distributed into each of the two new cells.
• Cytokinesis begins about the same time as
telophase so they often look alike. The two
daughter cells have the same number of
chromosomes as the parent cell.
• The cell then goes into - - - - - - - - - -
?
The cell cycle then goes back to the
Interphase stage
• Then it “rests” –but remember it is not really
resting but getting ready for the stages to
begin again.
Is there a difference between animal
and plant cells? Of course!!
• In animal cells during cytokinesis, the cell
membrane squeezes together around the
middle of the cell. The cytoplasm pinches into
two cells and each daughter cell gets about
half of the organelles.
So, what about the plant cell?
• It is different because plants cannot squeeze due to
their rigid cell walls. Instead a cell plate forms across
the middle of the cell. The cell plate gradually
develops into a new cell wall. A new cell membrane
develops between the two new daughter cells and
the cell walls form.
OK Review time--• Cell cycle:
Are you ready to see what you can
recognize?
• This is the __________________stage
• What happens here?
It’s Anaphase
• I think of it as little A’s being pulled towards
the ends of the cell’s poles. The sister
chromatids are actually separated and pulled
to opposite poles of the cell
Now this---name the stage
• What is happening?
Interphase!!!
• Did you get it right?
• Remember this is when the cell grows to its
mature size, makes a copy of its DNA and
prepares to divide into two cells. The
centrioles are also are copied.
How about this one?
• Remember that
• this one looks like another one that follows it and
they actually happen almost at the same time.
Telophase!!
• The chromosomes stretch out and lose their
rod-like appearance and a new nuclear
envelope forms around each region of the
chromosomes---then finally…….
•Cytokinensis
Now for your assignment:
• Using your journal and a textbook—turn to a new
page in the journal and use today’s date and the
topic of “The Cell Cycle”
• Turn to page 58-59 C in your book-using ½ page
each drawing-draw the stages and write what is
happening from your pages for each phases of
the stages. Basically you are copying what you
see into 3 pages of your journal. Get to work—Be
sure to draw them in order and color (Easier to
see what is going on).
Again---get to work!!!!