Post on 13-Mar-2020
Chapter 10
Cell Growth and Division
Cell Division
Before a cell becomes too large, it undergoes cell division,
in which the cell divides and becomes 2 “daughter” cells.
Before cell division occurs, the cell replicates all of its DNA.
Each daughter cell then receives its own copy of DNA, or
genetic information.
Each daughter cell has an increased ratio of surface area to
volume which allows for sufficient exchange of materials
with the environment.
Cell Division
In eukaryotes, cell division occurs in 2 main stages:
Mitosis- the first stage
Cytokinesis- the second stage- division of the cytoplasm
Many organisms, particularly unicellular organisms,
reproduce via mitosis and cytokinesis. This is a form of
asexual reproduction, since the cells produced by mitosis are
genetically identical to the parent cell.
Mitosis is also the source of new cells when a multicellular
organism grows and develops.
Chromosomes Chromosomes carry the genetic information of an individual
organism, and are responsible for passing genetic information between generations.
Organisms have a characteristic number of chromosomes Humans have 23 pairs or 46 chromosomes.
Before cell division, chromosomes are replicated and form two identical “sister” chromatids. When the cell divides, the sister chromatids separate from each other. One chromatid goes to each of the two new cells. Each pair of chromatids is attached at the centromere, near the middle of the chromatid.
Centromere
Sister Chromatids
The Cell Cycle
The Cell Cycle- a series of events that cells go through.
During the cell cycle, a cell grows, prepares for division, and
divides to form two daughter cells, each of which begins the
cell cycle again.
Consists of 4 phases
M Phase- includes mitosis and cytokinesis
S Phase- chromosome replication, synthesis of DNA occurs
G1 – cells do most of their growing. In this phase, cells increase in size
and synthesize new proteins and organelles.
G2 – the shortest phase of interphase, organelles and molecules required
for cell division are produced. At the end of this phase, the cell is ready to
enter the M phase and begin cell division.
Inte
rph
ase
The Cell Cycle
M Phase
4 Phases of Mitosis
Prophase- first and longest phase (~50-60%) of mitosis.
Chromosomes become visible. Centrioles separate and move
toward poles.
Centrioles lie within The centrosome and helps
organize the spindle
which works to separate
the chromosomes.
Near the end of prophase,
the nuclear envelope begins
to break down.
Spindle
forming
Centriole
4 Phases of Mitosis
Metaphase- chromosomes line up across the middle of the
cell. Microtubules connect the centromere of each
chromosome to the two poles of the spindle.
Microtubules
connect to
centromere of
chromosome.
4 Phases of Mitosis
Anaphase- the centromeres that join the sister chromatids
split, allowing the sister chromatids to separate and become
individual chromosomes. Anaphase ends when
chromosomes reach opposite poles and stop moving.
New individual
chromosomes-
formed from sister
chromatids
4 Phases of Mitosis
Telophase- final phase of mitosis- nuclear envelope
re-forms, spindle breaks apart, and nucleus becomes visible.
Cytokinesis
Cytokinesis- Cytoplasm divides. Cytokinesis typically
occurs simultaneously with telophase. Each part now
contains its own nucleus, DNA, and cell organelles.
In plants, a cell plate forms between the divided nuclei and
gradually develops into a separating membrane.
Binary Fission
Binary Fission-
cells grow to double
their size and divide
to form two cells.
Occurs in
prokaryotes and
single celled
eukaryotes.
Single celled
eukaryotes must still
go through mitosis
prior to division.
Exit Slip
Name in order the stages of the cell cycle, beginning with the
G1 phase.
Warm Up Exercise
When you came in, you picked up a bag with 7 images from
the cell cycle.
Place the images in order as best you can, then compare with a
partner.
Once you have reached a consensus, write the letters on your
warm up sheet, and label each phase.
Finally, explain what happens during that specific phase of cell
division.
Regulating the Cell Cycle
Different types of cells go through the cell cycle at different
rates.
Experiments show that normal cells will reproduce until they
come into contact with other cells.
When cells come into contact with other cells, they respond by
not growing. This is called contact inhibition.
This demonstrates that controls on cell growth and division can
be turned on and off.
Contact Inhibition
Cell Cycle Regulators
Cells in mitosis are regulated by a series of proteins called
cyclins which increases and decrease during the cell cycle.
Internal Cell Regulation: proteins that respond to events
inside the cell. Allow the cell cycle to proceed only when
certain processes have happened inside the cell.
External Cell Regulation: proteins that respond to events
outside the cell. Direct cells to speed up or slow down the
cell cycle. (ie: growth factors)
Cyclins
A sample of cytoplasm
is removed from a cell
in mitosis.
The sample is injected
into a second cell in
G2 of interphase.
As a result, the second
cell enters mitosis.
Uncontrolled Cell Growth
Cancer- a disorder in which some of the body’s own cells
lose the ability to control cell growth.
Cancer cells do not respond to the signals that regulate the
growth of most cells. As a result, these cells divide
uncontrollably and form masses of cells called tumors that can
damage the surrounding tissues.
Uncontrolled Cell Growth
Benign- cancer cells typically remain clustered together and
are relatively harmless.
Malignant- cancer cells break away and metastasize from
the tumor. These can be carried elsewhere in the body.
Carcinogens- substances known to promote the
development of cancer.
Cancer/Stem Cell Discussion
Reading on pg. 253
BioDetectives video- Skin Cancer: Deadly Cells
Exit Slip
Anticancer drugs prevent microtubules from forming spindle
fibers. Why do you think these drugs might be effective
treatments for cancer?