Transcript Cell Division Chapter 8

Short Review– All organisms start life as a single cell.
-like begets like
These two phrases are the basis for
CELLULAR REPRODUCTION
(Cell Division)
What do you think would happen if cells didn’t look exactly like the one
they were replacing????
Cells have a life cycle much like the organisms they compose.
Millions of cells die or a digested by your body everyday.
Cellular Reproduction helps replace them so you don’t run out of cells.
Prokaryotic cells rely on cell division for reproduction only.
They use a process called: BINARY FISSION
-they literally “split into two”
-must duplicate all cytoplasm, cell membrane,
DNA material and ribosomes before they do.
Eukaryotic cells don’t rely on cell division for reproduction. They use it
for other purposes:
1. Growth—from infant to child to adult, seed to seedling to plant
-hormones involved in this process
-can be made in lab now and injected to help avoid midget
http://www.popularmechanics.co.za/wp-content/uploads/2012/11/Earlyhuman-embryo.jpg
http://www.nobelprize.org/nobel_prizes/medicine/laureates/2010/early_human_embryos
_photo.jpg
2. Replacement—of worn out
cells.
http://1.bp.blogspot.com/LMyk8uUjo8c/Tk9vibMiKeI/AAAAAAAAAEA/i4rSNR
K8XaA/s1600/Apoptosis.gif
http://tfloto.files.wordpress.com/2010/04/apoptosis.jpg
-cells have life times just like we
do. When they get worn out,
they need to be replaced with an
exact copy to make sure the
same job
continues to be done.
3. Repair—healing of wounds, broken bones
-cell division helps rejoin the skin or bone ends
-wound healing starts on outside and progresses inward
-bone healing begins with broken pieces and new cells
“fill in” the gap created by the break
-what purpose do stitches and pins have??
http://guineapigmall.com/files/brokenbones.jpg
http://images.ddccdn.com/enc/images/images/en/stitches19630.jpg
Eukaryotic cells have many parts in them that must be duplicated in
order to ensure each cell is identical.
One of those parts is the Chromosome…which carries the DNA inside
the nucleus of the cell.
A single chromosome must copy
it’s entire network of information
and pass it onto a new
Chromosome for the new cell.
The new copy of the chromosome
will remain attached to the old one
for most of the division process.
http://www.clt.astate.edu/mhuss/chromosome.jpg
The two copies of the chromosome are called “SISTER CHROMATIDS”
They are joined at the CENTROMERE, or the “middle” of the “X”
During division, they will separate at the centromere and information
will be the same in each new cell.
Centromere
Sister Chromatids
DNA is replicated in the first stage of cell division…INTERPHASE.
Scientists once believed that interphase was a resting stage for the cell,
but have since found out that it is actually a very busy stage.
Interphase has 3 steps:
G1—cell organelles, such as ribosomes and mitochondria, will
double in content. Cytoplasm will double, cell membrane will
double
S—this is the stage where the DNA will double. At the end of
the “S” stage, the sister chromatids will be formed.
G2—the cell prepares for division here by increasing the
membrane proteins, increasing the energy supply and
anything else it needs to do to divide.
At the end of Interphase, the cell is ready to begin the
actual act of dividing the cell into two new ones.
Cells spend the majority of their time in interphase.
(approximately 90% of their lifecycle)
Division of the nucleus is called MITOSIS
Requires 4 steps to happen:
1. Prophase—the nuclear membrane begins to disintegrate to
allow the chromosomes to move outside of it into the
cytoplasm. The chromosomes also shorten and
thicken and are finally visible under a microscope. The
mitotic spindle also begins formation during prophase.
2. Metaphase—chromosomes will move to the cell equator and
line up. Spindle fibers, formed in the spindle region,
will attach to the chromosome centromeres from each
end.
3. Anaphase—the spindle fibers begin to shorten, pulling the
sister chromosomes apart and in opposite directions.
4. Telophase—chromosomes finally reach opposite poles of the
cell and a new nuclear membrane forms.
At this point, we have divided the nucleus but still have just one cell.
CYTOKINESIS will complete the division process.
-is the division of the cytoplasm and other organelles besides the
nucleus
-happens two different ways in plants and animals
-Plants have the formation of a new cell wall from inside to out…
vesicles inside the cytoplasm join to form a new cell wall
-Animal cells have cytoplasmic cleavage from outside to in
microfibers in the cell membrane help constrict the cell like a
string around a balloon creates two ends
-Why can’t plants have cytoplasmic cleavage???
New cell
wall
forming
Cells cannot just divide whenever they want.
There is a special unit of control mechanisms that help signal cells to
start and stop division.
1. The growth hormones present in cells trigger cell growth. Without
the hormones present, the cell will not start the mitosis process.
These are chemical messengers in the cells produced by the
body. Each cell type has a specific growth hormone for it.
What class of macromolecules do hormones belong to?
2. Cells must be touching other cells in order for division to start.
3. When the cell division process has
completed it’s job, Contact Inhibition
will signal a stop to the division.
This is triggered by one cell touching
another cell.
When Cell Cycle control mechanisms are not obeyed…
CANCER…occurs.
Cancer cells are no different than other cells in your body, they just
Don’t pay any attention to directions to stop dividing.
Therefore, cancer
cells will continue
the division process
even after healing or
replacement has
occurred and the
extra cells will
stack up on one
another causing the
formation of a tumor.
Two types of tumors can form:
Benign—these are localized tumors and will not spread. They
stay in the area they were started in. This does not make them a
“safe” cancer…if they are in an area where the tumor can block
the function of a vital organ they can cause death.
Malignant—these tumors will spread away from the point of
origin and can start new tumors in other parts of the organism.
They are not always fatal, but can be more difficult to attack in
some instances than benign tumors are.
Malignant tumors metastize…meaning they can spread to
other parts of the organism and continue the division process
producing more tumors far away from the point of origin.
There are 4 different types of cancer:
1. Carcinoma—cancer of the skin or external or internal coverings
of the body…like the intestinal lining.
2. Sarcoma—cancer of the muscles and bones (body support system)
Does not include the bone marrow.
3. Lymphoma—cancer of the lymph nodes, glands and lymph system
4. Leukemia—cancer of the blood and blood forming tissues such as
bone marrow
Types of Cancer:
Carcinoma—
Basal cell carcinoma
Malignant melanoma
Sarcoma--
Sarcomas– of the upper palate (human mouth) and a cat femur
Lymphomas—
Hodgkin’s Lymphoma
http://www.inflammation-information.com/images/hodgkinslymphoma.jpg
http://cancertreatmentwecareindia.com/lymphoma/images/_41381321_lymphoma.gif
Lukemias—
Abnormal
leukemia cell
http://disability-claims.net/images/leukaemia.gif
http://www.medindia.net/patients/calculators/images/most-commoncancers.jpg
Skin cancer is the most common of all cancers.
--accounts for nearly half of all cancers in the United States
-- More than 2 million cases of basal and squamous cell skin cancer
are found in U.S. each year.
--Melanoma, the most serious type of skin cancer, will account for
more than 75,000 cases of skin cancer in 2012.
From-http://www.cancer.org/cancer/cancercauses/sunanduvexposure/skin
-cancer-facts
--Melanoma is the fifth most common cancer for males and seventh most common for females.2
--The number of women under age 40 diagnosed with basal cell carcinoma has more than
doubled in the last 30 years; the incidence of squamous cell carcinoma among women under
age 40 has increased almost 700 percent.22
An estimated 45,060 new cases of invasive melanoma in men and 31,630 in women will be
diagnosed in the US in 2013.2
http://www.skincancer.org/skin-cancer-information/skin-cancer-facts#men/women
Cancer treatments vary according to type…
Surgery will cure some cancers. Benign tumors can, in some
instances, be cut away and not return.
Radiation—”burn” cancer cells using targeted beams of high energy
light. Generally only attacks actively dividing cancer cells.
However, may target actively dividing “good” cells as well.
Can cause nausea and hair loss among other side effects.
Chemotherapy—”poisons” cells using drugs to target actively dividing
cells. Target cell in different stages of division. Why target the
stages of cell division??
Drug
Action
Vinblastin
Prevents spindle formation
Periwinkle/Madagascar
Taxol
Freezes spindle after forms
to prevent function
Bark of Pacific Yew
Bryostatin 1
no effect on normal cells
only cancer
Bugula neritina
(ocean invert)
Esteinascidin 743 promising with difficult cancers
Source
Esteinascidia turbinata
(sea squirt)
Side effects of chemo differ from drug to drug as does effectiveness on
different types of cancer.
Best type of cancer treatment is PREVENTION.
Eat a diet high in fiber and low in fats.
Exercise regularly.
Don’t worship the sun or tanning beds.
If you must be outside, wear protective
creams and clothing.
Be tested for cancer regularly and/or be aware of signs of cancer.