Transcript adult stem cells

Team Starting Question
• Where did we all come from?
• How did the different types of
cells that we are made from
originate?
• How did our bodies become
organized?
Homunculi in Preformationism
Preformationism, a philosophical theory of heredity,
claimed that either the egg or the sperm (exactly which was a
contentious issue) contained a complete preformed individual
called a homunculus. Development was therefore a matter of
enlarging this into a fully formed being.
The term homunculus was later used in the discussion of
conception and birth, Nicolas Hartsoeker discovered
"animalcules" in the semen of humans and other animals. This
was the beginning of spermists' theory, who held the belief that
the sperm was in fact a "little man" (homunculus) that was
placed inside a woman for growth into a child. This seemed to
them to neatly explain many of the mysteries of conception. It
was later pointed out that if the sperm was a homunculus,
identical in all but size to an adult, then the homunculus may
have sperm of its own.
The spermists' theory also failed to explain why children
tend to resemble their mothers as well as their fathers, though
some spermists believed that the growing homunculus
assimilated maternal characteristics from the womb
environment in which they grew.
Homunculi in sperm as drawn by N.
Hartsoecker in 1695
1. Preformationism is the idea that
A. Embryos develop from a single cell.
B. Humans develop from a fully formed but
small body.
C. Small human forms were carried in the
egg only.
D. None of the above.
2. Spermists believed all of the
following except:
A. Sperm contained “animalcules.”
B. Sperm contained fully formed humans.
C. Sperm combined with the egg to produce
a zygote.
D. All people were contained within Adam.
We now know that we came from a single
cell produced by the union of an egg and a
sperm during fertilization!
That cell looks like this.
It is known as a zygote.
How is the first cell of an organism
produced? Reproduction!
Sexually
• involves two cells
(egg & sperm) joining
to make a new cell
(zygote) that is NOT
identical to the
original cells
Asexually
• involves a single cell
dividing to make 2
new, identical
daughter cells
So how did we get from a single
cell to where we are now?
Embryo
• Video human embryonic development
3. Humans develop from
A.
B.
C.
D.
A homunculus
A single cell known as a zygote
A sperm
An egg
4. How many layers of cells are
there in the gastrula?
A.
B.
C.
D.
1
2
3
4
5. Together, the layers of early
cells in the gastrula
A. Form just a few types of tissues
B. Form all of the different types of tissues
C. Form different types of tissues only in
humans
"It is not a simple life to be a single
cell, although I have no right to say
so, having been a single cell so long
ago myself that I have no memory
at all of that stage of my life."
—Lewis Thomas (1913–1993) author,
biologist, physician
NEWS FLASH! A MAMMAL IN YOUR
BIOME IS HAVING A BABY!
Investors want the public to know the details
to improve interest in the biodome!
What do we need to know about
cells to help us report on the
baby’s development?
Cells must divide for:
a) growth and development
b) repair of damaged tissue
c) replacement of worn/used tissue
d) Reproduction (in many simple
living things such as bacteria)
To grow from one cell to many, a
cell must make copies of itself.
• These copies must contain all
the right materials for life to
continue.
• For example, each “daughter”
cell produced from a “parent”
cell must have all the DNA of
the parent?
• A complete copy of DNA is
crucial because it contains the
instructions that tells the cell
how to work.
DNA (the friend that
won’t go away)
1. DNA contains
sequences of
chemical letters.
2. These letters code
for particular
proteins.
3. Proteins are the
machines and tools
of the cell.
 Therefore, having
the right DNA code is
essential if the cell
wants to be able to
function correctly
Scientists can actually watch cells divide under
the microscope, and they have been able to
figure out the rules of division by carefully
observing the process, much as someone could
gradually learn the rules of a game like football
or chess by watching it played repeatedly.
There are two kinds of cell division:
MITOSIS
• mitosis is for growth and
maintenance
• a duplication process
• produces two genetically
identical "daughter" cells from
a single "parent" cell
• replaces cells lost through
everyday wear and tear
(replenishment of skin cells)
• takes place in cells in all parts
of the body, keeping tissues
and organs in good working
order
MEIOSIS
• meiosis is for sexual
reproduction
• only a few special cells are
capable of meiosis: those that
will become eggs in females
and sperm in males
Help!
Someone
dropped the slideslet’s put mitosis back in the
correct order!
What did you
notice about the
chromosomes?
The instructions for
making cell parts
are encoded in the
DNA, so each new
cell must get a
complete set of the
DNA molecules.
DNA must be copied or replicated before
cell division.
Each new cell will then have an identical
copy of the DNA.
Mitosis: Let's Split!
Mitosis is the most dramatic event in a cell's life.
Cellular structures that have always been there
suddenly disintegrate, new structures are constructed,
and it all culminates in the cell splitting in half.
Mitosis is divided into six phases:
1. Prophase
The first five phases do the job
2. Prometaphase
of splitting the nucleus and its
3. Metaphase
duplicated genetic
4. Anaphase
information in two, while in
the final step, the entire cell is
5. Telophase
split into two identical
6. Cytokinesis
daughter cells.
MITOSISPROPHASE
MitosisPrometaphase
MitosisMetaphase
Mitosis-Anaphase
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Mitosis-Telophase
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CYTOKINESIS
• cleavage of the cell into equal halves
• in animal cells – constriction of actin filaments
produces a cleavage furrow
• in plant cells – plasma membrane forms a cell
plate between the nuclei
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MITOSIS
Typical eukaryotic cell cycle begins when the cell is
produced by mitosis and runs until the cell undergoes
its own mitosis and splits in two.
The cycle is divided into distinct phases:
G1 (gap 1)
S (synthesis)
G2 (gap 2)
M (mitosis)
C (cytokinesis)
Mitosis only occupies a fraction of the cycle.
The rest of the time-phases G1through G2—is known as interphase.
INTERPHASE
 Scientists used to think of interphase as a resting
phase during which not much happened, but
they now know that this is far from the truth.
 It is during interphase that chromosomes—the
genetic material—are copied, and cells typically
double in size.
 In contrast, most of these activities cease during
mitosis while the cell focuses on dividing.
 Not all cells in an organ undergo mitosis at the
same time.
 While one cell divides, its neighbors work to keep
the body functioning.
A typical animal cell cycle lasts roughly 24 hours,
but depending on the type of cell, it can vary in
length from less than 8 hours to more than a
year. Most of the variability occurs in G1.
G1 Phase
 First
growth stage
 Cell increases in size
 Cell prepares to copy its DNA
Synthesis Phase
 Copying of
all of DNA’s
instructions
 Chromosomes duplicated
G2 Phase
 Time
between DNA synthesis &
mitosis
 Cell continues growing
 Needed proteins produced
M Phase
 Cell
growth & protein production
stop
 Cell’s energy used to make 2
daughter cells
 Called mitosis or karyokinesis
(nuclear division)
How does the cell "know" when a
step has been completed and it's
time to move on to the next?
Control of the Cell Cycle
The cell cycle is controlled at three checkpoints:
1. G1/S checkpoint
-the cell “decides” to divide
2. G2/M checkpoint
-the cell makes a commitment to mitosis
3. late metaphase (spindle) checkpoint
-the cell ensures that all chromosomes are
attached to the spindle
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Apoptosis
•Apoptosis is programmed cell death and involves
a sequence of cellular events involving:
•fragmenting of the nucleus,
•blistering of the plasma membrane, and
•engulfing of cell fragments by macrophages
and/or neighboring cells.
•Cell death is a normal and necessary part of
development: frogs, for example, must destroy tail
tissue they used as tadpoles, and the human
embryo must eliminate webbing found between
fingers and toes.
•Death by apoptosis prevents a tumor from
developing.
Red Light! Green Light!
You are a cell!
 To proceed you must note the name of the
phase and what you must do as a cell
before you continue!
 As a group of 6- 3 will be the cell
checkpoints at G1/S , G2/M, and late
metaphase
 If you do not do so correctly, you could
turn into something much worse!

Sometimes go signals are
produced when they
shouldn't be, or stop signals
aren't sent or heeded. Both
scenarios can result in
uncontrolled cell division
and cancer. Mitosis then
becomes a weapon turned
against the body, spurring
the growth of invasive
tumors.
Cancer Metastasis
There is only one type of cell that is completely
generic—its gene expression is tuned so broadly that it
has unlimited career potential to become any kind of
cell in the body.
These undifferentiated cells cease to exist a few days
after conception.
They are embryonic stem cells.
http://www.hhmi.org/biointeractive/media/human_emb_dev-lg.mov
Long after our embryonic stem cells have differentiated, we
all still harbor other types of multitalented cells,
called adult stem cells.
These cells are found throughout the body, including in
bone marrow, brain, muscle, skin, and liver.
They are a source of new cells that replace tissue damaged
by disease, injury, or age.
Researchers believe that adult stem cells
lie dormant and largely undifferentiated
until the body sends signals that they are
needed.
Then selected cells morph into just
the type of cells required.