II. THE PROKARYOTIC CELL: BACTERIA
B. CELL STRUCTURE OF THE DOMAIN BACTERIA: An Overview
The overall purpose of this Learning Object is to list the various structures that make up a typical bacterium. These will be considered in detail in subsequent Learning Objects.
2. single-celled, microscopic organisms (Two exceptions have been discovered that can reach sizes just visible to the naked eye. They are Epulopiscium fishelsoni, a bacillus-shaped bacterium that is typically 80 micrometers (µm) in diameter and 200-600 µm long, and Thiomargarita namibiensis, a sperical bacterium between 100 and 750 µm in diameter.)
3. generally much smaller than eukaryotic cells.
4. very complex despite their small size.
In this section we are going to look at the various organelles or structures that make up a bacterium. We will not deal with the Archaea in this course but rather will concentrate on the Bacteria.
Structurally, a typical bacterium usually consists of:
- a cytoplasmic membrane surrounded by a peptidoglycan cell wall and maybe an outer membrane;
- a fluid cytoplasm containing a nuclear region (nucleoid) and numerous ribosomes; and
- often various external structures such as a glycocalyx, flagella, and pili.
Because a cytoplasmic membrane surrounds all cells in nature, we will start with this structure. Next we will study the bacterial cell wall. Then we will look at structures located within the cytoplasm. Finally we will examine those structures that lie external to the cell wall.
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