1. The Fundamentals of Life
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1.2. Cell Theory
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The microscope
van Leeuwenhoek's microscope
 Antonie van Leeuwenhoek (1632-1723). |
 Leeuwenhoek's microscope. |
Antonie van Leeuwenhoek is credited with constructing the first microscope.
- Size: matchbox
- Held close to the eye
- Magnification: 400x
van Leeuwenhoek was the first to describe sperm and (probably) bacteria, which he called "animalcules" ("little animals").
 Sperms, as van Leeuwenhoek saw them. |
 van Leeuwenhoeks drawings of "little animals" (animalcules). |
Hooke's microscope
The light from an oil lamp (K) was focused on the specimen (M) with the help of a water-filled sphere (G).
Hooke also drew what he saw through his microscope.
- Publishes "Micrographia" with detailed drawings of the "little life".
- Coins the term "cell"
 Hooke's drawing of a flea. Note the amount of detail in the image! |
 This sample of bark from cork oak was what made Hooke think of monastery cells. |
In a sample from cork oak, Hooke sees what he describes looking like cells in a monastery. Although nobody at the time knew what a (biological) cell is, Hooke coined the term "cell".
A modern light microscope
The parts of a modern light microscope.
A modern light microscope works essentially the same way as Hooke's microscope, although the design has changed quite a bit.
What characterizes a cell?
All cells have
- a cell membrane,
- cytoplasm (fluid-like intracellular substance), and
- DNA (in one or several chromosomes).
 Scanning electron microscope image of some E. coli bacteria. Each cell is about 2 μm long. |
 Epithelial cells stained with methylene blue. The cells are approx. 60 μm across. |
 Plant cells from yellow onion stained with methylene blue. The cells are approx. 200 μm long. |
What the cell theory says
- All organisms consist of one or more cells.
- The cell is the fundamental living unit.
- New cells may only arise from other cells.
What do you need to build a cell?
Polysaccharides
Polysaccharides are made from sugar.
Examples:
- Cellulose
- Starch
- Glycogen
Proteins
 Proteins are very large molecules. |
 Proteins are made of amino acids strung together in a long, long chain. |
Lipids
Lipids are a diverse group of fat or fat-like molecules, insoluble in water.
Fats are made of glycerol and fatty acids.
Phospholipids have a hydrophilic head and two hydrophobic tails.
Cell membranes are made of phospholipids.
The cell membrane is a double layer of phospholipids.
Nucleic acids
Nucleic acids are made of nucleotides.
The nucleic acids are DNA and RNA.
Backbone
- Alternating sugar (S) and phosphate (P) residues.
Nucleobases
- A always base pairs with T (in RNA, T is replaced with U), and vice versa.
- G always base pairs with C
