Transcript Differentiation and Stem Cells

Biology is the only subject in
which multiplication is the same
thing as division…
Regents Biology
2006-2007
Where it all began…
You started as a cell smaller than
a period at the end of a sentence…
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And now look at you…
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How did you
get from there
to here?
Getting from there to here…
 Going from egg to baby….
the original fertilized egg has to divide…
and divide…
and divide…
and divide…
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Why do cells divide…
 One-celled organisms


for reproduction
asexual reproduction (clones)
amoeba
 Multi-celled organisms

for growth & development
 from fertilized egg to adult

for repair & replacement
 replace cells that die from
normal wear & tear or from injury
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starfish
Dividing cells…
 What has to be copied
DNA
 organelles
 cell membrane
 lots of other
molecules

 enzymes
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plant cell
animal cell
Copying DNA
 A dividing cell duplicates its DNA
creates 2 copies of all DNA
 separates the 2 copies to opposite ends
of the cell
 splits into 2 daughter cells

DNA
cell
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nucleus
 But the DNA starts
loosely wound in
the nucleus
 If you tried to divide
it like that, it could
tangle & break
Organizing & packaging DNA
DNA
cell
nucleus
DNA has been
“wound up”
DNA in chromosomes in
everyday “working” cell
cell
nucleus
4 chromosomes
in
thisBiology
organism
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DNA in chromosomes in cell
getting ready to divide
Chromosomes of Human Female
46 chromosomes
23 pairs
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Chromosomes of Human Male
46 chromosomes
23 pairs
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Copied & Paired Up Chromosomes
centromere
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double-stranded
human chromosomes
ready for mitosis
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DNA must be duplicated…
chromosomes in cell
DNA in chromosomes
cell
nucleus
4 single-stranded chromosomes
duplicated chromosomes
duplicated
chromosomes
Biology chromosomes
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double-stranded
cell
nucleus
 MITOSIS

The nucleus
divides into two
 CYTOKINESIS

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The cell divides in
two
New “daughter” cells
 Get 2 exact copies of original cells
same DNA
 “clones”

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Mitosis in whitefish embryo
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onion root tip
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Remember where it all began…
You started as a cell smaller than
a period at the end of a sentence…
How did that
become you?
Billions and
billions of cells
that are all of a
specific type…
You have lots of cells that are each of a different type. They
become that different type through a process called
differentiation.
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Let’s connect the menu activity to differentiation.
Creating a menu
 Each of you had 11




cookbooks to work with.
You chose the recipe that
was necessary for your
particular event.
The food will be prepared.
Your party becomes a
specific type of party!
Once the party starts, you
can’t change the theme in
the middle.
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Inside the cell
 Every cell has 23 pieces of




DNA to work with.
Only the genes necessary
for a particular cell will be
“turned on” or expressed.
Those particular proteins
will be synthesized by the
cell.
The cell becomes a
specialized type of cell!
Once the cell differentiates,
it can’t develop into a
different kind of cell.
Remember where it all began…
You started as a cell smaller than
a period at the end of a sentence…
AD: Since these cells have the
potential to become all types of
cells they are totipotent.
Since all cells in
the embryo stem
from these cells,
we call these…
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Stem cells can also be adult.
 One example are stem cells in your bone marrow
that can become all kinds of blood cells.
AD: Since these cells have the potential to
become multiple types of cells, but not all,
they are pluripotent.
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How are stem cells like the stem of a plant?
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What do you remember?
 Humans, pets, and petunias all pass
through an early stage of development
called a(n) ………
 Embryo
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What do you remember?
 Cells become ………….. through the
process of differentiation.
 Specialized
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What do you remember?
 Most cells in the adult human body are
no longer capable of ………………..
 Differentiating
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What do you remember?
 Which is an example of a totipotent
cell?
A. Blastocyst
B. Bone cell
C. Fertilized egg
D. Lymphocyte
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What do you remember?
 Adult stem cells are best described as
A. Multipotent
B. Pluripotent
C. Totipotent
D. Unable to differentiate
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