Eukaryote Cells and Prokaryote Cells
Cells are the basic units of living organisms. Some organisms are
single cells (e.g. bacteria and yeast) and some are made of many cells
(e.g. animals). Generally, cells are capable of harvesting
energy and useful materials from their surroundings, synthesizing various
molecules that they need for their life cycle, duplicating themselves,
and eliminating waste byproducts of all this activity.
One way of thinking about a cell is as a little factory, importing some
raw materials, perhaps exporting some finished materials, and in the process
producing quite a bit of garbage! We want to think about these factories
and the machines in them from a physics point of view - this means doing
experiments to measure their physical propreties, and then thinking about
mathematical models for them.
We will just note that all living things are divided into two
broad classes, based on the structures of their cells:
-
Prokaryotes - cells which have no internal compartments, and therefore
which have their contents all mixed together in one space. Most important,
the DNAs of prokaryote chromosomes are just mixed together with everything
else in the cell. Prokaryotes are unicellular organisms.
Famous examples include
Escherichia coli (the most heavily
studied and best understood organism in biology)
Bacillus subtilus (another heavily
studied bacterium)
-
Eukaryotes - organisms made of cells with internal compartments, most importantly
a cell nucleus which contains the genetic DNAs, or chromosomes.
Some eukaryotes are just one cell (yeast) and some eukaryotes have many
cells (humans). But all eukaryotes have a cell nucleus!
Famous examples include yeast, fungi and plants, e.g.
Saccharomyces cerevisiae (baker's yeast)
Aspergillus nidulans (common mold, a type
of fungus)
Zea mays (corn)
and animals
Caenorhabditis elegans (a heavily studied
nematode)
Drosophila melanogaster (fruit fly - not
the common house fly!)
Mus musculus (house mouse)
Homo sapiens (you)
Xenopus laevis (a big south american toad)
Notopthalamus viridescens (great eastern
red-spotted newt)
So, there are prokaryote cells and eukaryote cells. A lot of what
we discuss will apply to both (e.g. the structures and many of the functions
of biomolecules in prokaryotes and eukaryotes are nearly the same).
But when we come to discuss the structure of cells, we will see that the
structure of our cells is much closer to those of baker's yeast than to
E. coli.
You may wonder about the ordering of the animals above. They are
roughly in order of increasing amount of DNA per cell. And newts
don't have a bit more DNA - they have about 10 times the DNA of human cells.
You might also be interested to know that tulips have about 5 times as
much DNA per cell as humans.
Additional reading: Chapter 5 of Darnell, Lodish and Baltimore