Question

Which of the following components are found in the cell walls of gram-positive bacteria but not gram-negative bacteria? A. Cytoplasmic membrane B. Lipopolysaccharide C. Outer membrane D. Peptidoglycan E. Teichoic acid

Short answer

The component found in the cell walls of gram-positive bacteria but not in gram-negative bacteria is Teichoic acid (Option E)

Step-by-step solution

Identify the components of gram-positive bacteria cell wall

Gram-positive bacteria cell wall mainly consists of a thick layer of peptidoglycan and teichoic acid.

Identify the components of a gram-negative bacteria cell wall

The gram-negative bacteria cell wall is composed of a thin layer of peptidoglycan surrounded by an outer membrane that contains lipopolysaccharides.

Compare the components and identify those present in gram-positive but not in gram-negative bacteria

After comparing, it can be observed that teichoic acid is present in the cell walls of gram-positive bacteria but absent in gram-negative bacteria cell walls.

Key concepts

Gram-negative bacteria

Gram-negative bacteria are a type of bacteria that are characterized by their unique cell wall structure. The cell wall of gram-negative bacteria is more complex compared to gram-positive bacteria. This complexity is due to several key components:

• They have a thin layer of peptidoglycan, which is a structural molecule that provides strength and rigidity to the bacterial cell.
• Unlike gram-positive bacteria, they possess an outer membrane that is external to the peptidoglycan layer.
• This outer membrane contains lipopolysaccharides (LPS), which are large molecules that protect the bacteria and can trigger immune responses in host organisms.
• The outer membrane also contains proteins and other molecules that help in transport and interaction with the environment.

The presence of an outer membrane in gram-negative bacteria is significant because it adds an additional barrier that makes these bacteria more resistant to certain antibiotics, detergents, and other substances. This structural feature is why they often pose more challenges in medical treatments.

Peptidoglycan

Peptidoglycan is an essential structural component in the cell walls of bacteria. It is particularly important due to its role in maintaining cell shape, providing strength, and protecting against osmotic pressure:

• Peptidoglycan consists of sugars and amino acids that form a mesh-like layer outside the plasma membrane.
• In gram-positive bacteria, this peptidoglycan layer is thick and can consist of multiple layers, which is why gram-positive cells can retain the crystal violet stain used in the Gram stain procedure.
• In contrast, gram-negative bacteria have a much thinner peptidoglycan layer situated between their inner and outer membranes.

The thickness of the peptidoglycan layer in different types of bacteria can significantly impact how they react to antibiotics. For instance, many antibiotics, such as penicillin, target the synthesis of peptidoglycan, making it essential for bacterial cell wall integrity.

Teichoic acid

Teichoic acids are important polymers found in the cell wall of gram-positive bacteria. These acids play several crucial roles:

• Teichoic acids provide structural support by reinforcing the thick peptidoglycan layer.
• They can help in the regulation of cell wall expansion and division during bacterial growth.
• These molecules are also involved in attracting cations like calcium and magnesium, which are important for cellular processes.
• Teichoic acids may play a part in pathogenesis, acting as adhesins that allow bacteria to attach to host tissues.

In gram-positive bacteria, teichoic acids are either bound to the peptidoglycan layer (wall teichoic acids) or embedded in the cellular membrane (lipoteichoic acids). Their absence in gram-negative bacteria is one of the distinguishing factors between the two groups. Understanding the roles of teichoic acids aids in comprehending how gram-positive bacteria maintain their robust structure and interact with their environments.