Download Mitosis PPT

The Cell Cycle, Mitosis,
and Cancer
Why can’t we be one big cell?
• There are limits to cell growth:
• DNA “overload”
– DNA is the blueprint for proteins
– Big cells lead to “information overload”
• Cell/DNA cannot make all of the proteins
that it needs
Example—if we only had one copy of
the biology book for the whole school
Why can’t we be one big cell?
• Exchange of materials
– Diffusion is only fast/efficient over short
distances
– Getting enough nutrients, waste, etc.
in/out becomes too difficult in a big cell
Why can’t we be one big cell?
• Surface area to volume ratio
– Volume increases much faster than
surface area
– Cell membrane does not have enough
area to allow all nutrients and waste to
diffuse in and out efficiently
Parameters
Case
I
Case
II
Case
III
Case
IV
Length (L)
1
2
3
4
Face Area (L2)
1
4
9
16
Volume (L3)
1
8
27
64
Surface Area(L2 x 6 faces)
6
24
54
96
Area/Volume ratio
6
3
2
1.5
How do we grow and
get bigger if cells can
only be so big?
CELL DIVISION
Cell Division and the Cell Cycle
• Cell cycle: the ‘life cycle’ of a cell
–A “parent” cell grows, prepares,
and then divides to form two
identical “daughter” cells.
–Includes interphase and mitosis
1 parent cell
Cell grows,
DNA duplicates,
Cell pulls apart
2 identical
daughter cells
Cell Division
• Mitosis is asexual reproduction. Each cell
receives its own set of DNA, but there is
NO GENETIC DIFFERENCE between the
parent and daughter cells.
Where Does Mitosis
Occur?
Nails
Skin
Hair
Intestines
Bones
Muscles
In other words…
Mitosis occurs here,
there, and everywhere
(almost!)
—Old
McDonald
Cells that DO NOT Undergo Mitosis
Cell Division
• Mitosis occurs only in somatic
(body) cells
– Gametes (sex) cells undergo
another process, called meiosis.
– (We’ll talk about that later.)
Cell Division
• Humans have 23
chromosome pairs.
After mitosis,
how many TOTAL
chromosomes
does each cell
have?
The cell cycle
INTERPHASE: G1
• Cell
grows rapidly (G for growth)
- The cell grows, makes proteins,
and serves its purpose in the body
Interphase: S
•S
phase; DNA is copied
- S for “synthesis”
Chromosomes
New cells must be exactly like
the original - DNA is copied
before division can begin
Genetic information (DNA) is
found in the nucleus
Sister chromatid
centromere
Interphase: G2
• Cell grows more, makes more
organelles, and prepares for mitosis
(cell division) --- “get ready 2 go”
G2 checkpoint helps maintain
genetic (DNA) stability by
repairing/stopping the
replication of damaged cells.
---Important focus in
understanding cancer
END OF INTERPHASE
The Life of a Cell
Mitosis
(M phase)
Interphase
M phase
• Cell
divides into 2 identical
daughter cells
• Daughter cells are identical to each
other and to the parent cells
• Mitosis is divided into 4 phases
(P, M, A, T)
P = Prophase
• Longest phase of mitosis
• DNA (chromatin) coils up
and condenses to form visible
chromosomes
• Nuclear membrane breaks
up
• Spindle fibers form
•Centrioles (animals only)
begin to migrate to opposite
ends of the cell
M = Metaphase
• Chromosomes are
connected to
spindle fibers at
their centromeres
• Chromosomes line
up across the
Middle of the cell
Sister chromatid
centromere
A = Anaphase
• Centromeres split
Apart
• Spindle fibers pull
chromatids to
opposite poles of
the cell
T = Telophase
• Chromosomes
uncoil
• Spindle fibers
break down
• Two new nuclei
start to form
Cytokinesis
• Occurs after
mitosis
• Cytoplasm
divides
• Cells pinch apart
Cytokinesis in Plants
• In plants, a cell plate forms to divide
the cells and becomes the cell wall
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE/CYTOKINESIS
Put the following stages of mitosis
(interphase, prophase, metaphase, anaphase,
telophase/cytokinesis in order.
d
c
a
b
D, A, C, B, E
e
What happens when…
MITOSIS GOES WRONG…?
CAUTION…
• You’re about to learn about one of biggest
human killers in all of the world.
• Responsible for 7.6 million deaths…
• …in 2007 alone.
• 7.6 Million is roughly equal to the entire
population of North Carolina.
• The deadly killer?
CANCER
Cancer
• Uncontrolled cell
division
• May be caused by:
– Environmental
factors
– Changes in enzyme
production in the
cell cycle
Normal Control of the Cell Cycle
• Enzymes (cyclins) control the cell cycle
– Series of enzymes monitor the cell’s progress
from phase to phase
Controlling Cell Division
- Cells have internal & external
regulators that control cell division
- Cancer cells do not respond to the
regulators, which leads to uncontrolled cell
growth
- Cancer cells can form tumors
* benign tumors
* malignant tumors (metastasize)
Unregulated Cell Growth
Celebrities with Cancer
• Cancer doesn’t discriminate – anyone is
susceptible, and anyone can be diagnosed.
• BUT, why is it that some groups seem to be
more prone to cancer than others?
Why do doctors think cancer might
be genetic?
• Certain mutations
within our cells
can
be inherited from
one of our parents
Genetics Involved in Cancer
• Two genes involved in cancer that we
will talk about are:
– Oncogenes
– Tumor Suppressor Genes
Oncogenes
• Oncogenes code for proteins that initiate/start cell
division (they tell the cell “Hey - start dividing!”)
Tumor Suppressor Genes
• Code for proteins that stop the cell from dividing
(they tell the cell “Hey – stop dividing!”)
Development of Cancer
• Cancer can develop when:
– an oncogene is mutated AND one TS
gene is mutated
– OR when both tumor suppressor genes
are mutated
• It’s like treading water – you use both arms to
stay above water, but even if you take away
one arm you can manage to stay afloat. But,
if you take away both arms, you have no
arms to tread water with and you sink.
Development of Cancer
• When two of these genes are mutated, cell
division is no longer regulated, and the cell
divides uncontrollably, forming a mass of
cells known as a tumor.
Why are tumors dangerous?
• Tumors can have a dangerous impact
when they form around tissues that
are sensitive and vital.
• They put pressure on nearby tissues
and organs.
THE EFFECTS OF A TUMOR
IN OUR BODY
Why are tumors dangerous?
• Cancerous cells can also invade
other tissues/organs, damaging or
disabling them in the process.
• This makes our tissues and organs
more susceptible to infections.
How does cancer spread?
• Cells that form a tumor are called
“malignant”
• Tumor cells continue to produce cells via
mitosis, and the tumor releases those
malignant cells into the blood stream
• In the blood stream, these cells are
exposed to the immune system…
How does cancer spread?
• Cells that survive the attacks from our
immune system travel through our body,
and they can adhere to muscle linings,
tissues, or other organs.
• Tumor formation begins in a new location
of the body as these malignant cells begin
to divide in the new location.
• This process is called metastasis
Metastatic Colon Cancer
Why is Cancer more common in
older people?
• With every cell division, the risk of DNA
mutation increases
Cells in their body have
already been through many
divisions and many cycles.
Each time a cell divides
and copies its DNA, it
increases the risk of a
genetic mutation
Take a skin cell versus a
bone cell. In which would a
mutation be more likely to
Cancer Treatments
Surgery
Doctors may choose to
physically remove a tumor
with surgery. They may also
remove some healthy tissue
as a preventative measure
to make sure that all
potentially malignant cells
are removed and that
metastasis is not an option.
Cancer Treatments
Chemotherapy
Chemo is a treatment for cancer that stops a
certain process in our body. What would you
guess it stops?
*Hint: it usually inhibits the oncogene in our cells
What are some side effects of chemotherapy?
Cancer Treatments
Not only does chemo stop the division of malignant
cells in our body, it stops division of ALL the cells
in our body. Thinking back to the side effects of
chemo, what cells are being affected? Where did
division stop?
Closing Question
How does mitosis
relate to cancer?