10 Questions
What is the main purpose of the bacterial cell wall?
To maintain the shape of the cell
What is the composition of the Gram positive bacterial cell wall peptidoglycan layer?
N-acetyl muramic acid and N-acetyl glucosamine
Where are teichoic acids located in bacterial cell walls?
In the outer layer of Gram positive cell walls
Which molecules are responsible for cross-linking in the peptidoglycan layer of the cell wall?
Tetrapeptides linked by penta peptides
What is the significance of the thick peptidoglycan layer in Gram positive bacteria?
It provides resistance to certain antibiotics like penicillins
Why is digestion necessary for large molecules in bacterial cells?
Because large molecules cannot readily pass through membranes
Why can't Mycobacteria be gram stained?
High lipid content in the cell wall
Why are wall-less bacteria often produced when treated with lysozyme or antibiotics that interfere with peptidoglycan biosynthesis?
Because lysozyme and antibiotics target the cell wall
Which group of bacteria naturally lack a cell wall?
Mycoplasma
How does the lack of a rigid cell wall affect Mycoplasma?
It makes them susceptible to antibiotics
Study Notes
Cell Wall Function
- Maintains the shape of the cell
- Supports the weak cytoplasmic membrane
- Plays a role in cell division
- Responsible for staining properties of the organisms
- Rigid and protects the cell from osmotic lysis
Gram Positive Cell Wall
- Thicker peptidoglycan layer compared to Gram negative bacteria
- Composed of alternating N-acetyl muramic acid and N-acetyl glucosamine
- Cross-linked by identical pentapeptides and tetrapeptides
- Site of action for penicillins, cephalosporins, and lysozyme enzyme
Teichoic Acids
- Polymers of glycerol phosphate or ribitol phosphate
- Located in the outer layer of Gram positive cell wall
Cell Wall of Gram Negative Bacteria
- Outer membrane, peptidoglycan, and periplasmic space
- Digestion is necessary for molecules to pass through the outer membrane or cell membrane
Acid-Fast Bacteria
- Mycobacteria have an unusual cell wall with high lipid content (fatty mycolic acids)
- Cannot be Gram stained due to high lipid content
Wall-Less Forms of Bacteria
- Mycoplasma: the only group of bacteria that exist naturally without a cell wall
- Lacking a rigid cell wall, resulting in no defined shape
- Resistant to antibiotics that destroy bacterial cell walls
Induced Wall-Less Forms
- Produced when bacteria are treated with enzymes that are lytic for the cell wall (e.g. lysozyme)
- Or when antibiotics interfere with peptidoglycan biosynthesis
- Usually generates non-viable organisms
Test your knowledge on the structure and functions of bacterial cell walls. Learn about the differences between Gram positive and Gram negative bacteria cell walls, as well as the important roles they play in maintaining cell integrity and function.
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