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Cell Growth - Differentiation & Specialization
Stem Cells
How does your body grow bigger?
Heal an injury?
Cells reproduce!
The process by which a cell splits into two new daughter cells is
called cell division.
How many cells did we start out as?
Zygote
Blastocyst
Embryo
A Stem Cell Story
Fetus
Cell Differentiation is the process in which a cell develops into a
specific type of cell within a multicellular organism.
• Ex) Brain, muscle, bone, nerve cell
The original cell or stem cell changes in response to triggers from
the body or itself into different cells.
Stem Cells & Differentiation
WHAT ARE STEM CELLS?
Stem Cells are undifferentiated (unspecialized) cells that can…
• Create other kinds of cells that specialize through differentiation
• Create more stem cells
NOVA - Replacing Body Parts
CBS 60 Minutes - Growing Body Parts
TED Ed - Stem Cells
Research on stem cells
• Medical researchers believe
that stem cell therapy has the
potential to dramatically
change the treatment of
human disease.
• A number of adult stem cell
therapies already exist,
particularly bone marrow
transplants that are used to
treat leukemia.
Research on stem cells
Potential uses of stem cells
A Stem Cell Story
Potential problems
• One concern of treatment is the risk that transplanted stem cells
could form tumors and become cancerous if cell division continues
uncontrollably.
• Medical vs. Ethical Debate (embryonic cells)
Science Show - Stem Cells
What Can Stem Cells Do?
NOVA - Replacing Body Parts
All cells reproduce.
Cell Growth
Does an animal get larger because each cell
increases in size or because it produces more
of them?
Cell Growth
• As you might have guessed, living things grow
by producing more cells.
• The koalas have the same size cells, just one
has more then the other.
Limits to Cell growth
• The larger a cell becomes, the more demands
the cell places on its DNA. In addition, the
cell has more trouble moving enough
nutrients and wastes across the cell
membrane.
• The cell can’t grow. It must reproduce!
Cell Division
• The process by which a cell divides into two
new daughter cells is called cell division.
• Before cell division occurs, the cell
replicates, or copies, all of its DNA. This
replication solves the info. problem.
Cell Division
• What do you think would happen if a cell
were simply to split into two without any
advance preparation?
Chromosomes
• In eukaryotic cells, the genetic
information that is passed on from
one generation of cells to the next
is carried by chromosomes.
• The cells of every organism have
a specific number of
chromosomes.
• Each chromosome consists of two
identical “sister” chromatids.
When the cell divides, the “sister”
chromatids separate and go to
each of the new cells.
Chromosome
• Each pair of chromatids is attached at an area
called a centromere.
• Centromeres are usually located near the
middle of the chromatids, although sometimes
can be found at each end.
The Cell Cycle
• The cell cycle is the series
of events that cells go
through as they grow and
divide.
• During the cell cycle:
- A cell grows
- Prepares for division
- And divides to form two
daughter cells
Events of the Cell Cycle p)245
• There are four phases of the Cell Cycle.
• G1 phase – period where cell does most of
their growing
• S phase – chromosomes are copied and the
synthesis of DNA molecules takes place.
(DNA Replication)
• G2 phase – usually the shortest of the
phases. The phase where essential
organelles are constructed.
• and M phase – Cell Division.
I P on a MAT C
*preparation between split
Interphase
*mitosis
Steps of Cell Division
Prophase
Metaphase
Anaphase
Telophase
*cells split
Cytokenesis
Interphase
• Stage between cellular
division.
• Also known as the G1, S,
and G2 stages of the cell
cycle.
• In Interphase the cell is
allowed to grow, copy its
DNA and check for crucial
genetic mistakes.
Mitosis
• Mitosis (M phase) steps which include the
process for asexual cell division.
• Biologists divide the events of mitosis into
four phases:
- Prophase
- Metaphase
- Anaphase
- Telophase
Depending on the type of cell, the four phases
may last anywhere from a few minutes to
several days.
Prophase
-
The first and the longest phase of mitosis, prophase can take as much
as 50 to 60 percent of the total time required to complete mitosis.
- During prophase in animal cells, the centrioles
separate and take up positions on opposite
sides of the nucleus.
- The centrioles help organize the spindle,
fanlike microtubule structure that helps
separate the chromosomes.
Prophase
•
•
•
chromosomes
appear-chromatin
condenses to form
chromosomes
the nucleolus
disappears
the cell membrane
begins to break
down
Metaphase
• chromosomes align
along the equator of
the cell pulled by the
spindle fibers
• Spindle fiber that
are attached to the
poles connect to the
centromeres
• Short Phase
Early Anaphase
• chromosomes are
pulled to the poles
by the contraction of
the spindle fibers
chromatids are
separated at the
centromere
Late Anaphase
• chromosomes begin
to move to the
opposite poles
• Karyokinesis
• the energy for this
process is provided
by the mitochondria
Early Telophase
• the new cell wall
begins to form to
separate the new
cell the
chromosomes begin
to form a nucleus
Late Telophase
• the chromosomes
start to uncoil and
become less dense
• Nuclear membrane
reassembles
• Nucelolus reappears
• Plasma membrane
begins to separate
• Cell plate forms
• two new identical
cells are formed
Cytokinesis
• Cytokinesis is the
division of the
cytoplasm of a
parent cell.
• Microfilaments form
a ring around the
equator. When the
microfilaments
contract-pinches
makes a furrow
Cytokinesis
• You may either consider it
the end of Mitosis or the
beginning of Interphase.
• While each daughter cells
gets identical sets of DNA,
the cytoplasm and
organelles are only
roughly divided equally
between the two cells.
• Parent chromosome #=
Daughter chromosome#
Mitosis
• all four
stages of
mitosis can
be seen in
this picture.
note the
process by
which the
red and blue
chromosome
s separate.
MITOSIS
://www.youtube.com/watch?v=
VlN7K1-9QB0
http://www.youtube.c
om/watch?v=LEpTTol
ebqo
Regulating the Cell Cycle
• If we grow by cell division, then why do we stop
growing?
• Multi-cellular organisms cell growth is
controlled.
• For example, in the human body, most muscle
and nerve cells don’t divide at all once they
have developed, whereas skin cells and blood
cells divide rapidly.
Controls on Cell Division
• Look at Fig 10-7 on page 250. What is
happening in this figure? What would happen
if the cells continued to divide?
• When cells come into contact with other
cells, they respond by not growing.
• How does this relate to how your body
responds to a cut or a bone fracture?
Cell Cycle Regulators
• Scientists discovered
that cells in mitosis
contain a protein called
cyclin when injected in
a non-dividing cell,
would cause a miotic
spindle to form.
• Cyclins regulate the
timing of the cell cycle
in eukaryotic cells.
Other Cell Cycle Regulators
• Internal regulators- proteins that respond to
events inside the cell.
For example: several regulatory proteins make
sure that a cell does not enter mitosis until all
its chromosomes have been replicated.
- External regulators- proteins that respond to
events outside the cell.
For example: external regulators direct cells to
either speed up or slow down the cell cycle.
Uncontrolled Cell Growth
• Why is cell growth regulated so carefully?
• Cancer- a disorder in which some of the
body’s own cells lose the ability to control
division. Cancer cells do not respond to the
signals that regulate the division of most cells.
Skin Cells