1. Unit 7: Continues our exploration of
the common characteristics of all life,
growth and development: How cells
divide
2. Connection to Rivers
Obviously for life to
continue it must grow, and
reproduce.
This is true for river
organisms as well as any
other life forms.
Cultural eutrophication
creating Algal Blooms.
(rapid growth of algae
populaitons)
4. What Causes an Algal Bloom?
Excessive organic
pollution provides a
tremendous amount of
nitrogen and phosphorus
to the water.
Algae thrive/grow in these
conditions.
This is one example of cell
division gone amuck. (get
it…a muck!)
5. Cell Division-What important event must take
place before cells can successfully divide?
DNA replication!
Why?
Each new cell needs a copy
of the genetic information for
life.
What does the genetic
information in the DNA
sequence of neucleotides
code for?
The amino acid sequence to
synthesize (make) Proteins
6. WHY DO CELLS Need to
DIVIDE?
1. What happens to skin cells after you
get a cut?
2. What might happen if someone’s skin
cells did not continue to divide and
multiply as the person grew up?
3.How do bacteria reproduce? Can they
have sex?
7. WHY DO CELLS DIVIDE?
1. After you get a cut the good skin cells divide and
multiply to repair the broken tissue.
2. Skin grows and protects our internal organs. Your
skin, due to shedding of skin cells, replaces itself every
7 years. Actually, you skin sheds every 28-45 days!
~40,000 cells per hour, The dead skin needs to slough
off to allow the new cells to the top. We shed about 40
lbs. of skin in a lifetime!
3. Sorry bacteria, no sex. They use asexual cell
division to multiply! REPRODUCE!
8. Cells Divide for 3 Main
Reasons:
1. UNICELLULAR (one celled) ORGANISMS (both prokaryotic
and eukaryotic):
Reproduction of a new generation
(asexual reproduction)
MULTICELLULAR ORGANISMS:
2. Growth/Development
3. Repair of tissues
9. Why do cells Divide?
Close your packet and with your table
partner review the three main reasons
that cells divide.
10. Cell Division
In order to
understand cell
division you need
to realize that it
entails more than
DNA Replication.
There are many
steps that go into
a successful
division!
11. The Cell Cycle-What is a
cycle anyway?
The in a eukaryote cell, there
Cell Cycle :
is a repeating sequence of cellular
growth and division during the entire
life of an organism.
12. What cells might need to
use this cycle?
ANY CELL THAT NEEDS:
Growth
Tissue Repair
Asexual Reproduction
13. Introduction to The 4 Stages
of the Cell Cycle
1. Growth 1 (G1)
2. Synthesis (S)
3. Growth 2 (G2)
4. Mitosis (M)
14. In Summary:
The 4 Stages of the Cell
Cycle
INTERPHASE is long and consists of the first 3 stages in the cycle:
Growth 1 (G1)- cells grow and function normally here
Synthesis (S)- DNA is replicated
Growth 2 (G2)- preparation for nucleus division
MITOTSIS (M) is short and consists of 2 parts:
Mitosis - nucleus divides
Cytokinesis - cytoplasm divides
A closer look…
15. The 4 Stages of the Cell Cycle
(1)
Stage 1: G1 (Growth 1) - A cell grows
rapidly, and carries on routine functions.
Cells that do not divide (like some
nerve cells) stay in this stage
FOREVER!
For-e-ver!
16. The 4 Stages of the Cell Cycle
(2)
Stage 2: S (Synthesis) -
DNA is copied during this
stage
Who remembers what it
is called when DNA
makes an exact copy of
itself?
DNA Replication!
17. The 4 stages of the cell cycle
continued.
Stage 3: G2 (Growth 2) - In G2 phase, preparations
are made for the nucleus to divide
The first 3 steps, G1, Synthesis, and G2 are also
considered collectively as Interphase in a cell cycle,
more on this later.
Stage 4: M (Mitosis) - The process during cell
division when the nucleus of the cell is divided into
two nuclei. The DNA in each nuclei is identical!
(Cytokinesis) - The process during cell division
when the cytoplasm divides.
Cyto = Cytoplasm, and Kinesis = movement
18. Close your packet and review the cell
cycle with your table partner:
Remember there are 4 stages.
Which stages comprise interphase?
Which stage does the cytoplasm
divide?
During which stage does the DNA
replicate?
What stage insures that each new cell
gets an identical nucleus?
Which three steps make up something
called interphase?
19. Before we go into detail about the
steps of Mitosis, let’s take a look
at Chromosomes
Can you recall the function of a
Chromosome?
Consider them as the packages
for your genes (protein recipes)
What are they made of?
20. Chromosome-
Chromosomes are formed from
DNA .As you recall genes and
genetic information (genes) are
located on chromosomes in the
nucleus of a cell!
There can be hundred or
thousands of genes on each
chromosome.
During mitosis, chromosomes
condense to visibly form the
“super-coil” pictured to the right.
21. The “X” Shape of a newly
replicated Chromosome (DNA has
replicated.)
22. The “X” Shape of a Chromosome,
defined:
Sister Chromatids-
2 exact copies of one
strand of replicated
DNA, joined in the
center by a
centromere.
23. When cells are actively dividing they go
through the Cell Cycle/Mitosis (mitosis has its
own 4 steps + interphase.)
Step 1- I nterphase
Step 2- P rophase
Step 3- M etaphase
Step 4- A naphase
Step 5- T elophase
The first letter of the 5 steps in order is I-
P-M-A-T. That’s a crazy acronym that’s fun
to say…Try it and keep a straight face.
24. Let’s figure out what exactly is taking place
during each step of mitosis. Check out these
cells in their various stages of division.
25. What do you notice about the nucleus during
interphase ? Where are the chromosomes?
26. Preparation for Mitosis:
Step 1- Interphase (I for I ntermediate-
the cell is not actively dividing.)
During interphase, (G 1 , S, G 2 )
the cell grows to its mature size
and makes copies of its DNA. Each
copy is called a Sister Chromatid
these form during interphase,
although they are not visible.
27. The next step is called prophase , what do
you notice about the contents in the nucleus
now?
28. Step 2 of Mitosis: P rophase- P for
P icture (we can see the chromosomes
as they become visible in a light
microscope.)
The 3 things that happen during
prophase include:
Nuclear membrane breaks
down
Centrioles separate. Spindle
fiber network is formed. Like a
spider thread connected to the
chromosomes.
Chromosomes are thick and
dense inside the fading nuclear
envelope.
29. Now the cell enters the step called
metaphase, what do you notice
happening to the chromosomes now?
30. Step 3: Metaphase ( M for m iddle as the
chromosomes m igrate to the m iddle of
the cell.)
Metaphase, or “Middle”-
Chromosomes line up in the
middle of the cell
The centromere that holds
the sister chromatids
together attaches to the
spindle fibers
The cell is ready to split.
31. Step 4: Anaphase: Now look at the
chromosomes and describe what is
taking place. Pretty cool huh?
32. Step 4: A naphase (A is for a ction,) the newly
replicated chromosomes separate and move
away from each other.
Chromatids separate at the
centromere and move
towards opposite sides of
the cell.
The moment they separate
from each other the
separated sister
chromatids are now called
chromosomes.
Now each new cell will have
its own copy of the DNA!
Yippee!
34. Step 5: Telophase ( T is
for T wo)
Separated chromosomes
have moved completely
away from each other and
New Nuclear Membranes
begin to form around these
two groups of separated
chromosomes.
Now the cell membrane also
starts to pinch in two!
36. After Mitosis: Cytokinesis
Cytoplasm splits
Cytokinesis (literally
means that the
cytoplasm moves)
The final step in the
cell cycle. The
cytoplasm splits, and
two cells are now
present, identical to
one another!
37. What do you think happens next?
Remember it’s a cycle.
Cells will start the cycle over.
2 cells become 4, 4 become 8 and so
on.
If the cell cycle last 24 hours, how many
cells will be present in 2 weeks if you
start with just one cell?
38. Do we know our “C’s”???
Discuss these questions with your table
partner…
You started off with one cell, what is the
goal of mitosis?
What is a c hromosome?
What is a c entromere?
What is a c entriole?
What is a c hromatid?
39. Let’s look at some cells undergoing
Mitosis with the microscope.
We will examine prepared
slides of the root tip of an
onion plant.
Root tips grow very fast
Many of the cells were
actually caught in the act
of dividing when the slide
was made.
Using your microscope
skills see how many of
the stages of mitosis you
can see.
