Download Why do cells divide?

Why do cells divide?
QUIZ
1. Where does DNA synthesis occur ?(what
organelle?)
2. What does Helicase do? DNA polymerase
do?
3. What is the purpose of DNA synthesis?
4. Write down this DNA’s complimentary strand
1. G A T A C A
Since we say family members are “blood”
relatives, does that mean we share the same
blood?
•
You share no blood with anyone....not even your mother and
father! Your family shares DNA.
•
1⁄2 of your DNA came from your mother (egg) and 1⁄2 from your
father (sperm).
•
The process that made this possible is MEIOSIS which makes
the sperm and egg.
• A fertilized egg then grows into an organism by a different
process of cell division called MITOSIS.
 Cells divide to
maintain a workable
volume to surface
area ratio
Cells divide to maintain a workable
volume to surface area ratio
 Volume is the amount of
space inside of a cell.
 This would include the
cytoplasm and all of the
organelles.
Cells divide to maintain a workable
volume to surface area ratio
 Surface area is the total
amount of exterior which is
exposed to the environment
around the cell.
 This would include the
outside of the cell
membrane.
Cells divide to maintain a workable
volume to surface area ratio
 Volume increases faster
than surface area.
Cells divide to maintain a workable
volume to surface area ratio
 The surface area must
be large enough for a
sufficient amount
materials to enter the
cell.
 The materials must enter
quickly enough that all of
the cell will get what it
needs.
 Thus, a larger surface
area: volume ratio is
preferred.
Cells stay small to keep the rate of
diffusion fast!
Fill It In …
EXPLAIN which of the cell sizes pictured is
preferable.
Cells divide to make more cells
 Growth of a multicellular
organism requires the
addition of cells
 Larger organisms do not
necessarily have bigger
cells, but they will have
more cells than smaller
organisms.
Cells divide to make more cells
 Repair of damaged
tissues by replacement
of cells lost due to injury
or cell death requires
cell division.
 A healthy cell will divide
to replace the lost
cell(s).
Mitosis
Fill It In …
2 reasons that cells need to divide:
1.
2.
Cells divide to make more cells
 Cell division occurs at
different rates
depending on the
organism and the
type of cell.
Plant root cells would
divide more rapidly
because this is an area
of active growth
Cell division occurs at different rates
Some nerve cells enter
a phase of no division
 Called G0
 Why brain and nerve
damage is often
nonreversible
Cell division occurs at different rates
Some bacteria cells
divide very rapidly
For example, E. coli
can divide every 20
minutes in ideal
conditions.
How do cells divide?
Prokaryotic vs Eukaryotic Division
How do cells divide?
 The result of all cell
division is the
production of daughter
cells.
 In order for daughter
cells to contain enough
DNA, the genetic
material (DNA) of the
parent cell must be
copied.
How do cells divide?
 Prokaryotic division
differs from eukaryotic
division because
prokaryotic cells do not
contain a nucleus or
membrane-bound
organelles.
How do cells divide?
 Eukaryotic division
requires the replication
of the nucleus and
genetic material (DNA)
as well as the
allocation of the
organelles into each
daughter cell.
Fill It In …
Reason that prokaryotic cell division is
simpler than eukaryotic cell division …
Eukaryotic Cell Cycle & Mitosis
 Interphase is the
“normal” part of the
cell cycle.
 The cells spend most
of the cycle (life of the
cell) in interphase.
There are three stages in interphase
 G1 - Cell increases in
size and synthesize
new proteins and
organelles
There are three stages in interphase
 S - DNA is replicated
During most of interphase,
DNA exists in a “relaxed”,
stringy form called
chromatin
After being copied, there
are two complete copies of
the DNA in the cell.
These copies are attached
to each other.
There are three stages in interphase
 S - DNA is replicated
Each copy of DNA is called a
chromatid.
The two chromatids are attached
in a region celled the
centromere.
At this point in interphase, the
chromatids are
coiled/condensed
The entire structure is called a
doubled chromosome.
Structure of Chromosomes
There are three stages in interphase
 G2 - organelles and
molecules required
for cell division are
produced
Fill It In …
Differentiate between …
Chromatin Chromatid Chromosome -
Fill It In …
On the diagram of the cell cycle, HIGHLIGHT the
stages that are part of Interphase.
DRAW the
Cell Cycle
Stages of Mitosis (Eukaryotic Cell
Division)
 Prophase
Coiled chromosomes
become visible
Nuclear membrane is
broken down
Spindles (protein fibers that
attach to chromosomes and
aid in chromosome
movement) start to form
Stages of Mitosis (Eukaryotic Cell
Division)
 Metaphase
Spindle fibers attach to
the centromere regions
Chromosomes are
moved to the Middle of
the cell
Stages of Mitosis (Eukaryotic Cell
Division)
 Anaphase
Spindle fibers shorten
Doubled chromosomes
are separated into
chromatids
Chromatids begin to
move to opposite
poles/ends of the cell
Stages of Mitosis (Eukaryotic Cell
Division)
 Telophase
Spindle fibers are broken
down
Nuclear membrane
begins to form around the
clusters of chromatids at
each pole of the cell.
Cytokinesis
 Cytokinesis is the
separation of the
cytoplasm (including
all organelles) into
two identical daughter
cells.
Cytokinesis
 Animal cells constrict
in the middle to pinch
apart forming two
different cells.
Cytokinesis
 Plant cells also
produce a cell plate
dividing the two cells.
 This cell plate will
become the cell wall
MITOSIS Animation
Fill It In …
Summary of the cell cycle
1. Interphase
1. .
2. .
3. .
2. Mitosis
1.
2.
3.
4.
3. .
.
.
.
.
Mitosis & Cancer
 Typically, cell division
is controlled by genes
in the cell, contact
with other cells, and
available nutrients in
the environment.
 (molecules are found
on the surface of the
cell)
Mitosis & Cancer
 Cancer is a class of
diseases characterized
by uncontrolled cell
division and the ability
of these cells to invade
other tissues
(metastasis).
Mitosis & Cancer
 Cancer occurs when the
genes that control cell
division do not function
properly.
 This may occur because
of an inherited genetic
defect, a spontaneous
genetic mutation, or
mutation caused by
environmental factors.
Cancer and the
Cell Cycle
Cancer
Cancer Institute
The Cell Cycle and Cancer
The Stages of the Cell Cycle
CancerCancer cells do not respond to the signals that
regulate cell division
Creates a tumor (or mass of cells) that can
migrate throughout the body
Cyclin- regulates the cell cycle
There are several factors that regulate the cell
cycle and assure a cell divides correctly.
1.Before a cell divides,
the DNA is checked
to make sure it has
replicated correctly. (If
DNA does not copy
itself correctly, a gene
mutation occurs.
2. Chemical Signals tell a cell when to start and
stop dividing.
Neighboring cells communicate with dividing
cells to regulate their growth also.
Cancer is a disease of the cell cycle. Some of
the body’s cells divide uncontrollably and tumors
form.
Tumor in Colon
Tumors in Liver
DNA mutations disrupt the cell cycle.
Mutations may be
caused by:
1. radiation
2. smoking
3. pollutants
4. chemicals
5. viruses
While normal cells will stop dividing if there is a mutation in the
DNA, cancer cells will continue to divide with mutation.
Cell Suicide or Apoptosis
Cell damage—
no repair
First
mutation
Second
mutation
Third
mutation
Fourth or
later mutation
Uncontrolled growth
Due to DNA mutations, cancer cells ignore the
chemical signals that start and stop the cell
cycle.
Due to DNA mutations, cancer cells cannot communicate
with neighboring cells. Cells continue to grow and form
tumors.
Skin cancer
ABCD of Cancer
Regions of Highest Incidence
Regions of Highest Incidence
U.K.:
UK:
Lung
cancer
Lung
cancer
JAPAN:
Stomach
cancer
CHINA:
Liver
cancer
CANADA:
Leukemia
US:
Colon
cancer
AUSTRALIA:
Skin cancer
Cancer by State
BRAZIL:
Cervical
cancer
Mitosis and Cancer
1. Typically, cell division is controlled by genes in the cell,
contact with other cells, and available nutrients in the
environment.
2. Cancer is a class of diseases characterized by
uncontrolled cell division and the ability of these cells to
invade other tissues.
How Cancer Develops
Treating Cancers
Cancer treatments include surgery, chemotherapy,
radiation, or lasers.
SUMMARY
Normal Cell Division
1. DNA is replicated
properly.
2. Chemical signals start
and stop the cell cycle.
3. Cells communicate with
each other so they
don’t become
overcrowded.
Cancer Cells
1. Mutations occur in the
DNA when it is
replicated.
2. Chemical signals that
start and stop the cell
cycle are ignored.
3. Cells do not communicate
with each other and
tumors form.
Vocabulary
 cancer: term used to indicate a disease
characterized by abnormal cell growth
 mutagen: environmental factor that causes
mutations
 carcinogen: cancer-causing agent
 tumor: mass of growing tissue
benign: does NOT invade surrounding cells
malignant: spreads into nearby tissues
 metastasis: spread of malignant cells
 oncogene: gene that causes cancerous growth
Fill It In …
Cancer is caused by uncontrolled _______
___________, which may occur because
of
1.
2.
3.
Check Yourself!
1. Why is a large surface area: volume ratio preferable?
2. Name three reasons cells must divide.
3. Why is eukaryotic cell division more complex than
prokaryotic cell division?
4. What are the two basic stages of the cell cycle?
5. How is the genetic material “prepared” for cell division
during interphase?
6. How many daughter cells are produced as a result of
mitosis, and how do these cells compare to the parent
cell?
7. How are mitosis and cancer connected?
Check Yourself!
1. Why is a large surface area: volume ratio preferable?
KEEPS THE RATE OF CELL DIFFUSION FAST
Check Yourself!
2. Name three reasons cells must divide.
GROWTH
REPAIR
(ASEXUAL REPRODUCTION)
Check Yourself!
3. Why is eukaryotic cell division more complex than
prokaryotic cell division?
EUKARYOTIC CELLS CONTAIN A NUCLEUS AND
MEMBRANE-BOUND ORGANELLES
Check Yourself!
4. What are the two basic stages of the cell cycle?
INTERPHASE & MITOSIS
Check Yourself!
5. How is the genetic material “prepared” for cell division
during interphase?
CHROMATIN CONDENSES AND FORMS TWO
CHROMATIDS CONNECTED BY A CENTROMERE
THIS FORMS A DOUBLED CHROMOSOME
Check Yourself!
6. How many daughter cells are produced as a result of
mitosis, and how do these cells compare to the parent
cell?
2 CELLS ARE PRODUCED
THEY ARE GENETICALLY IDENTICAL TO THE
PARENT CELL
Check Yourself!
7. How are mitosis and cancer connected?
CANCER IS CHARACTERIZED BY UNCONTROLLED
CELL DIVISION