- Assignment 2.1
The cells of all living organisms have several things in common. All cells have a cellular membrane that separates them from the outside world, a cell without a cell membrane is not a cell. All cells uses DNA as their genetic material. All cells follow the central dogma to make proteins, many of which are enzymes. All cells contain the same types of macromolecules: carbohydrates, proteins, nucleic acids, minerals, fats and vitamins. All cells regulate what enters and leaves the cell by plasma membrane proteins. All cells undergo and are the result of cell division.

The type of cell(s) an organism has is one of the most basic characteristics of that organism. We can divide cells into two very different types based on their internal structure. The two types are called Prokaryotic and Eukaryotic. Current data support the theory that Prokaryotic cells were the initial or primitive cell type on earth and that Eukaryotic cell types evolved from them. Prokaryotic cells are smaller and less complex than eukaryotic cells (see the bacterium below).

Eukaryotic cells have a different internal organization than Prokaryotic cells, in that Eukaryotic cells contain many membrane-bounded internal structures, or Organelles, whereas Prokaryotic cells contain no internal, membrane-bound organelles. Much like your body, which contains internal structures (organs) specialized to perform a particular function, Eukaryotic cells contain internal structures (organelles) that perform specialized biochemistry. The membranes surrounding these organelles compartmentalizes the biochemical reactions that occur inside. For example, one type of organelle we will examine is the Nucleus. The Nucleus is surrounded by a phospholipid bilayer and contains the cell's DNA. Transcription of genes (DNA -> mRNA) occurs inside the nucleus.

In Prokaryotic cells, there are no internal, membrane-bounded structures. The DNA of Prokaryotes is "loose" in the cytoplasm. There is no nuclear membrane therefore, no actual nucleus. The cytoplasm of Prokaryotic cells is full of enzymes, mRNA, ribosomes, and other cellular stuff. It is just not compartmentalized by membranes.

Prokaryotes - A tour of a Bacterium (Click the round red button to start, then click again).

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