Microbiology, 2021

3.3 • Unique Characteristics of Prokaryotic Cells 89
Figure 3.15
hypotonic environments.
In cells that lack a cell wall, changes in osmotic pressure can lead to crenation in hypertonic environments or cell lysis in
Figure 3.16
In prokaryotic cells, the cell wall provides some protection against changes in osmotic pressure, allowing it to maintain its
shape longer. The cell membrane is typically attached to the cell wall in an isotonic medium (left). In a hypertonic medium, the cell
membrane detaches from the cell wall and contracts (plasmolysis) as water leaves the cell. In a hypotonic medium (right), the cell wall
prevents the cell membrane from expanding to the point of bursting, although lysis will eventually occur if too much water is absorbed.
CHECK YOUR UNDERSTANDING
• Explain the difference between cell morphology and arrangement.
• What advantages do cell walls provide prokaryotic cells?
The Nucleoid
All cellular life has a DNA genome organized into one or more chromosomes. Prokaryotic chromosomes are
typically circular, haploid (unpaired), and not bound by a complex nuclear membrane. Prokaryotic DNA and
DNA-associated proteins are concentrated within the nucleoid region of the cell (Figure 3.17). In general,
prokaryotic DNA interacts with nucleoid-associated proteins (NAPs) that assist in the organization and