Presence of cell wall in bacteria

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The bacterial cell wall is made of thick, rigid peptidoglycan that maintains the cell’s shape, protects the cell interior, and prevents the cell from bursting during osmosis.

In most prokaryotic cells, the cell wall provides support and helps cells resist mechanical pressures, but they are not solid so that materials can pass through rather easily.

Cells that have a cell wall are better able to withstand subtle changes in osmotic pressure and maintain their shape. In hypertonic environments, cells can become dehydrated, causing crenation or shriveling of the cell.

a) An isotonic solution is a solution that has the same solute concentration as another solution. There is no net movement of water particles, and the overall concentration on both sides of the cell membrane remains constant. The image shows a cell with 20% solute (80% water) in a beaker containing 20% solute (80% water). Arrows in and out indicate that water moves both into and out of the cell. b) A hypertonic solution is a solution that has a higher solute concentration than another solution. Water particles will move out of the cell, causing crenation. The cell in this image still has 20% solute concentration (80% water) but the cell is now in a beaker containing 40% solute concentration (60% water). An arrow shows water moving out of the cell and the cell shriveling. C) A hypotonic solution is a solution that has a lower solute concentration than another solution. Water particles will move into the cell, causing the cell to expand and eventually lyse. The cell in this diagram still has 20% solute concentration (80% water) but is now in a beaker containing 10% solute concentration (90% water). An arrow shows water mving into the cell and the cell swelling.

In cells that lack a cell wall, changes in osmotic pressure can lead to crenation. Crenation happens particularly in hypertonic environments, whereas cell lysis happens in hypotonic environments.

By contrast, cells that possess a cell wall undergo plasmolysis rather than crenation. In plasmolysis, the plasma membrane contracts and detaches from the cell wall. There is a decrease in interior volume, thus allowing the cell to maintain some shape and integrity for a while. Likewise, cells that lack a cell wall are more prone to lysis in hypotonic environments.

a) In an isotonic solution there is no net movement of water particles. The cell membrane is attached to the cell wall. The drawing shows a rectangular cell; the cell membrane is just inside the cell wall. Arrows indicate that water is moving both in and out. B) In a hypertonic solution water partices move out of the cell. The cell membrane shrinks and detaches from the cell wall (plasmolysis). The diagram shows a cell that has shriveled. Points of the cell membrane are still attached to the cell wall but most of the cell membrane has pulled away from the cell wall resulting in a star-shaped cell. Arrows show water leaving the cell. In a hypertonic solution water particles move into the cell. The cell wall counteracts osmotic pressure to prevent swelling and lysing. The image shows the same rectangular cell as in the isotonic solution except that the cell and cell wall are bulging outwards a bit. Arrows show water entering the cell.

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.

Penicillin can be used to break down the peptidoglycan wall as it inhibits the construction of the bacterial cell wall making the bacteria more prone to bursting.

MCAT Presence of cell wall in bacteria

MCAT Presence of cell wall in bacteria

Practice Questions

 

Khan Academy

Virulence factors of Listeria monocytogenes

 

MCAT Official Prep (AAMC)

Official Guide B/B Section Question 27

Biology Question Pack, Vol 2. Question 43

 

Key Points

• Bacterial cell walls are primarily composed of thick, rigid peptidoglycan.

• Most prokaryotic cells have a cell wall that helps the organism maintain cellular morphology and protects it against changes in osmotic pressure.

• The cell membrane changes shape when placed into different solutions based on their concentration of solutes, but the cell wall does not change due to its rigid structure.

• Penicillin inhibits the production of peptidoglycan in the cell wall.


Key Terms

Peptidoglycan: a polysaccharide-protein molecule

Plasmolysis: contraction of the membrane of a plant cell as a result of the loss of water from the cell

Osmosis: movement of water from a high concentration to low concentration over a semi-permeable membrane

Hypertonic: where the concentration of solutes is higher outside the cell than inside it

Crenation: shrinkage and acquire a notched or scalloped surface of a cell

Lysis: the disintegration of a cell by rupture of the cell wall or membrane.

Hypotonic: solution outside of a cell has a lower concentration of solutes relative to the cytosol

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