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Cell Theory
What is meant by “alive”?
What is a cell,
and how do we know it?
Are all cells the same?
(Well, no....)
Refer to chapter 4 in text.
What does it mean to be “alive”?
It’s ALIVE!
Requires energy
(from food, or from inorganic sources)
Requires nutrients
(even if energy is from, say, the sun)
Metabolism
Builds molecules… breaks molecules down, requires excretion
Maintains homeostasis
e.g. pH, fluid and nutrient levels, temperature?...
Reproduction
(self replicating)
Growth and/or development
(If it divides but never gets bigger…)
Some undergo profound metamorphosis.
Response: to the environment, and long-term adaptation
e.g. shivering, phototropism, kinesis…
Evolution is a long-term response to the environment.
May be structural and/or behavioral.
By default, such things also show organization (cellular to systemic).
(Mader lists: organized, energy/homeostasis, response, reproduction, adaptation.)
To be alive a thing must meet all of these criteria to some extent.
http://www.ted.com/talks/martin_hanczyc_the_line_between_life_and_not_life?language=en#t-296044
TED talk
Cell Theory…
What do you remember about it?
Anton van Leeuwenhoek (1632−1723)
first “microscope”, saw “animalcules”.
Robert Hooke (1635−1702)
working with cork,
coined term “cell” →
Robert Brown (1773−1858)
plant cell nuclei are important to viability
↓
http://www.google.com/imgres?q=light+micrograph+of+cell+nucleus&hl=en&safe=
http://www.chemheritage.org/EducationalServices/pharm/chemo/readings/timeline/hooke.jpg
History of cell theory
Jakob Schleiden (1804−1881)
all plants are made of cells or cell products - 1838
Theodor Schwann (1810−1882)
all animal tissues are also made of cells – 1839
Schleiden and Schwann are credited with defining cell theory,
though Schleiden wasn’t quite right on cell origin.
Rudolf Virchow (1821-1902)
is credited with adding the point about cell divisionthe third point made here.
(He seems to have stolen the idea from Robert Remak...)
So, what are the 3 points of cell theory?
You won’t need all of the dates,
but note it took nearly 200 years to pull this together.
Remember science grows in fits and spurts.
Reference for further reading:
Paolo Mazzarello Nature Cell Biology 1, E13 - E15 (1999) doi:10.1038/8964 A unifying concept: the history of cell theory
Cell Theory
1. Living organisms are composed of cells.
Fluorescent stain of cell
Cell Theory
1 Living organisms are composed of cells.
2. Cells are the smallest units of life.
-Smaller things certainly exist,
and may be components of cells,
but are not, themselves, alive.
Cell Theory
1. Living organisms are composed of cells.
2. Cells are the smallest units of life.
3. Cells come from pre-existing cells.
(Cell division may be for reproduction,
or for growth and development
in a multicellular organism.)
Stained DNA showing mitosis
Can you think of any exceptions
to cell theory?
Any fuzzy edges?
(muscle cells/aseptate fungal hayphae/kelp, extracellular matrices, viruses, protocells…)
To see things down to about 1 μm…
germhistory.net/Leeuwenhoek.aspx
www.microscopeworld.com/MSWorld/parts.aspx
This is the type of optical
device van Leeuwenhoek
used.
This is more like the
compound
that you will use.
What if things are too small to see this way?
www.steve.gb.com/science/electron_microscopy.html
Transmission Electron Microscopy:
An electron beam (not light)
is magnified by electromagnetic ‘lenses’
(not glass lenses), and the image is
detected by a phosphor screen (not your eye).
The sample is preserved, stained, embedded,
sliced and mounted on a holder.
The image is a cross section.
original.britannica.com/eb/art-110970/Scannin...
Scanning Electron Microscopy:
An electron beam creates an
indirect image as the electron beam
bounces off of a gold-plated specimen
to the detector.
The sample is dried and gold plated.
The image is of the surface.
(Often these are colorized)
flickr.com/photos/alanjaras/80145985
How big is a cell?
Note for IB:
(small) molecules
cell membranes
viruses
bacterium
organelles (up to…)
(most) cells (up to..)
1 nm
10 nm
100 nm
1 μm
10 μm
100 μm
Notice, though, the exceptional
cells illustrated above that!
Why are cells so small?
-As a cell gets larger,
it requires more nutrients,
and produces more heat
and metabolic waste.
-Nutrients enter,
and wastes leave,
through the surface membrane….
Multicellularity
Once many cells are working together as one organism,
they can show specialization:
e.g., nerve, muscle, bone and skin cells.
The organism shows emergent properties
which arise from the contributions of the specialists:
The whole is greater than the sum of its parts.
(Remember in the inorganic chemistry...?)
e.g. sexual reproduction, complex immunity,
thought...
You were originally a single cell,
and all of your complexity arose from there.
Every nucleated cell in you body has the same information:
The difference is which genes are turned on or off.
Embryonic stem cells are totipotent or pluripotent…
… they can become anything in you.
www.bioedonline.org/.../slide01.cfm?tk=24&dpg=8
Specialization, (cont.)
You still have adult stem cells:
They may be multipotent
e.g., blood cells of all sorts arise from
blood stem cells in bone marrow.
(RBC’s couldn’t divide if they wanted to…)
… or unipotent:
- can only become one
type of cell, but are
able to divide, unlike
their successor cells.
e.g. muscle stem cells.
www.siteman.wustl.edu/PDQ.aspx?id=1202&xml=CD
...
Clinical uses of stem cells:
Current:
- bone marrow transplant for treating certain leukemias
Pending:
-replacement of neuron insulation (to date only in rats)
-in clinical trial stage for Stargardt’s disease
(juvenile macular degeneration) ↓ blog by trial participant
http://www.aisquared.com/blog/2013/08/looking-back-my-one-year-participation-in-a-stem-cell-clinical-trial
-pluripotent lines to repair cns damage
Stem cells are also used extensively in research
that is not directly connected to therapies.
Opposition arises due to
- concern about the sources of stem cells
- concern about unknown effects
- concern about possible whole-organism cloning
- others?
Compare (and contrast – implicit in any IB “compare” question)
light, SEM,and TEM, giving applications for each.
Provide the contributions of any 4 people
in the early study of cells.
Explain why cells are the size they are.
Are they all the same size?
Cell theory: Pretty solid, but…?
Give your stance on stem cell therapy,
along with your defense,
and at least one argument for the other view
that you feel is credible.
Cell Theory
van Leeuwenhoek
Hooke
Brown
Schleiden
Schwann
Virchow
light microscope
transmission electron microscopy
scanning electron microscopy
multicellularity
specialization
emergent
embryonic stem cells
totipotent
pluripotent
adult stem cells
multipotent
unipotent