Transcript 15-16 Pre AP Cell Differentiaiton notes

Cell Differentiation=Cell Specialization
http://www.pbslearningmedia.org/resource/tdc02.sci.life.stru.different/cell-differentiation/
Lesson Essential Question
For today’s lesson we have one main
question to answer:
Why is Cell Differentiation an
important part of the development of
a multicellular organism?
Topics for Discussion:
1.
2.
3.
4.
5.
What is cell differentiation?
How are stem cells related to
differentiation?
What makes a cell a stem cell?
What are 2 main types of stem cells?
Identify misconceptions about stem cell
research.
What is Cell Differentiation?
Cell Differentiation=Cell Specialization
 It is a process.
 And in this process, a cell becomes
“specialized” for a specific structure or
function during multicellular development.

Why is cell differentiation directly related
to STEM CELLS?
Well, stem cells are the ones able to
differentiate
 Stem cells are unique cells.
 They have several abilities:

1. The can divide and renew
themselves for long
periods of time.
2. They can remain
undifferentiated in form.
3. They can develop into another
type of cell (differentiate).
Pause and Connect:
Take a minute and examine this diagram. In your
notebook write one sentence describing what this
diagram tells you as a biologist.
What, then, makes a blood cell different from a
skin or muscle cell, or a leaf cell from a root
cell in a plant?
The answer lies in the way each cell
“deploys” or utilizes its genome.
 In other words, the particular combination
of genes that are turned on (expressed) or
turned off (repressed) dictates cellular
structure and function.

What does this mean exactly? And
How does it happen?
All of the cells within a complex multicellular
organism, such as a human being, contain the
same DNA. Correct?
 BUT, each cell expresses this DNA differently.


Actually, a cell’s location within the embryo
helps determine how it will differentiate.

First, it is decided which
genetic information will
be expressed, thereby
indicating the type of
cell that is to be formed.

Then, through cell
differentiation, those
instructions are carried
out and specialized cells
are formed.

Thus, different cells can have very different
physical characteristics despite having the
same genome.
Think about this process as DNA
being a cookbook….

When you want to make
a specific dish, you select
that recipe from the
cookbook and carry out
its instructions….

The same way, cells only
express specific genes it
needs to carry its
function.
When does differentiation occur?

Differentiation occurs numerous times during
the development of a multicellular organism.

As the organism changes from a simple zygote
to a complex system of tissues and cell types.

Differentiation is a common process in adults
as well: adult stem cells divide and create fully
differentiated daughter cells during tissue repair
and during normal cell turnover.
Let’s Describe Major Types of Stem
Cells:
Embryonic Stem Cells





Totipotent: cell can develop
into all cell types.
Can self-renew indefinitely
Plentiful
Embryos used in research is
4-5 days old: it is a ball of
cells
Left over embryos from IVF
procedures. They are mostly
donated.
Adult Stem Cells
Multipotent: cell can develop
into a few cell types but not
all.
 Hard to find.
 Body cells (somatic) found in
organs and tissues.
 They are called “adult”
because they are found after
an embryo develops into a
fetus and are no longer an
embryonic stem cell.

Examples of Specialized Cellsblood cells
◦ Red blood cells carry Oxygen to body cells.
◦ White blood cells protect us from infection
by attacking foreign
substances.
White blood cell
Red blood cells
Muscle Cells

Muscle cells are specifically designed to
contract, to cause movement. Their long,
cylindrical shape is perfect for contracting.
Epithelial Cells

Epithelial cells are
found on biological
surfaces. They can be
designed for protection,
absorption, secretion,
etc.
In Plants:
Specialized “hair cells” on
roots are designed to
increase absorption of
water and nutrients,
through increased surface
area.
 Other cells in roots are
designed for growth, and
protection.


Plant stems have
cells that are
specialized for
transporting
water, nutrients,
etc. throughout
the plants.
Leaves of plants have many kinds of
specialized cells.
 Guard cells open and close to let out
water vapor and allow for gas exchange.
 Palisade cells have many chloroplasts for
carrying out photosynthesis.

Putting it all together….
In all previous examples, the particular
combination of genes that are turned on
(expressed) or turned off (repressed) has
dictated or determined:
1.
2.
How these cells work
And what they look like…
Stem Cell Debate and Misconceptions

Many people oppose stem cell research as they
believe that the 4-5 day old embryo is a living
human being.

What some do not understand is that unused
embryos are discarded regardless.

Some believe it is better to use these embryos for
research on how to cure human diseases rather
than discarding them away without purpose.
Misconceptions
Pregnancy, fetuses or babies are aborted or
harmed in stem cell research.
Fertilized Blastocysts donated from IVF labs
are used and no pregnancy is aborted.
 The fertilized embryos are removed from
women’s bodies and used for research.
The embryos are left over from IVF and are
frozen and are not implanted for pregnancy.

Misconceptions

A clone is grown in a lab without an embryo or
born from a mother and is the same age and
personality as you, and has no belly button.
A clone would need a fertilized embryo and
would have to be implanted in a woman’s
uterus. If you were cloned at 14, the clone
would be 14 years younger than you (a baby
you) and would have to have a mother to be
born, so yes, it would have a belly button.
Misconceptions
If the embryos were not used in stem cell
research they would have been used to make
children.
The embryos left over from IVF are discarded.
 Men and women who donate their embryos do
not know that their embryos are used for
research.
The embryos used in scientific research are
donated with written and informed consent
(permission) by the donors.

Lesson Essential Question
To answer our essential question:
Why is Cell Differentiation an
important part of the development of
a multicellular organism?
It is essential because one kind of cell
cannot perform all the activities required
for life.