01 Intro to the Cell Essay

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Unit 1 Introduction to the Cell historical light microscopy and the discovery of the cell, cell theory facts, hypotheses, theories and the scientific method
‘strands’ of cell biology – cytology, biochemistry, genetics basic properties of cells classes of cells prokaryotes - two kingdoms

eukaryotes membrane-bound compartments nucleus endomembrane system – ER, Golgi, lysosomes, vesicles mitochondria, chloroplasts origins of eukaryotic cells - endosymbiont theory cytoskeleton model organisms in cell biology
1

The Cell Theory: a Brief History
Robert Hooke 1635-1703
• first microscope
• viewed slices of cork
“cellula” (little rooms)

2

History, con’t
Antoni Van Leeuwenhoek 1632-1723
• worked with glass  huge improvement in quality of lenses  nearly 300x magnification became possible
• first to observe:
• single-celled organisms “animalcules”
• protists from pond water
• bacteria from his mouth
“father of microbiology”
• blood cells
• banded pattern in muscle cells
• sperm from ...

3

Drawings by Leeuwenhoek, 1670s

Fig 1-31

• progress stalled for a century or so ...
• limited resolving power
• emphasis on description rather than explanation
• 1830s – compound microscope
• improved magnification and resolution
• allowed visualization of objects less than 1 μm

5

What can we see?

fun website re relative sizes
Fig 1-6

fun website (from neutrinos to galaxies)

6

Beginnings of Cell Theory
1833 Robert Brown (botanist)
• noticed that every plant cell contained a round structure
• ‘kernel’ nucleus 1838 Matthias Schleiden (another botanist)
• all plant tissues are composed of cells
• embryonic plant always arose from a single cell
1839 Theodor Schwann (zoologist)
• similar observations in animal cells
• recognition of structural similarities btw plants and animals! • Cell Theory formulated by Schwann
7

Cell Theory
• all organisms consist of one or more cells
• the cell is the basic unit of structure for all organisms added 20 years later:
• all cells arise only from pre-existing cells

How can this only be a ‘theory’?

8

Facts and the Scientific Method fact: • something we know to be true …
• something we believe to be true … fact (scientific):
• an attempt to state our best current understanding,
• based on observations and experiments

• valid only until revised or replaced by a better understanding, based on more careful observations or more discriminating experiments

9

What is the Scientific Method?
• make observations
• use inductive reasoning to develop tentative explanation (hypothesis)
• make predictions based on your hypothesis
• make further observations or design and carry out controlled experiments to test your hypothesis
• interpret your results to see if they support your hypothesis 10

Then what is a theory?
• a hypothesis that has been tested critically
• under many different conditions
• by many different investigators
• using a variety of different approaches
• by the time an explanation is regarded as a theory it is widely accepted by most scientists in the cell
• the “solid ground” of science
• evolution, germ theory, cell theory

11

What is more solid than a theory?
• If a theory is thoroughly tested and confirmed over many years by such large numbers of investigators that there is no doubt of its validity … it may eventually be regarded as a law.
• gravity
• laws of thermodynamics
• laws that govern behaviour of gases

Biologists are very conservative about using the term law.

12

‘Strands’ of Cell Biology bio-chemistry fermentation done by cells!

synthesis of urea in lab
Hooke
looks at cork cytology 1600s

Brown every cell notes comes nuclei from a cell

Krebs cycle glycolysis

genetic code DNA
Dolly
double the helix sheep! 1930s

1800s

Leeuwenhoek
Schleiden & stains & dyes looks at lots Schwann formulate
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