Question

Which of the following statements True? a. Gram-positive bacteria have a single cell wall formed from peptidoglycan. b. Gram-positive bacteria have an outer membrane. c. The cell wall of Gram-negative bacteria is thick, and the cell wall of Grampositive bacteria is thin. d. Gram-negative bacteria have a cell wall made of peptidoglycan, while Grampositive bacteria have a cell wall made of phospholipids

Short answer

a. True, b. False, c. False, d. False

Step-by-step solution

Identifying the characteristics of Gram-positive bacteria

Gram-positive bacteria have a thick cell wall made of peptidoglycan. They don't have an outer membrane. Therefore, the statements a and b can now be assessed. Statement a is correct, Gram-positive bacteria do have a cell wall formed from peptidoglycan. However, statement b is incorrect - Gram-positive bacteria do not have an outer membrane. Their structure contains just one lipid bilayer, unlike the structure of Gram-negative bacteria.

Identifying the characteristics of Gram-negative bacteria

Gram-negative bacteria have a thin layer of peptidoglycan and an additional outer membrane. This makes them more resistant to antibiotics than Gram-positive bacteria. Thus, statement c is wrong - the cell wall of Gram-negative bacteria is thin, not thick, and the cell wall of Gram-positive bacteria is thick, not thin. Moreover, statement d is partially correct. Gram-negative bacteria do have a cell wall made of peptidoglycan, but it's thinner than the wall of Gram-positive bacteria. However, Gram-positive bacteria do not have a cell wall made of phospholipids, they have a cell wall made of peptidoglycan. Therefore, statement d is incorrect.

Key concepts

Gram-negative bacteria

Gram-negative bacteria are a unique group characterized by their cell wall structure. Unlike Gram-positive bacteria, they possess a thin peptidoglycan layer and an additional outer membrane. This outer membrane is critical because it contains lipopolysaccharides that can act as endotoxins, potentially causing strong immune responses in hosts.
The outer membrane serves as a protective barrier, making Gram-negative bacteria more resistant to certain types of antibiotics. This structure supports their survival in harsher environments compared to their Gram-positive counterparts.
Learning about the outer membrane's effectiveness can help in understanding how to treat infections caused by Gram-negative bacteria.

• The peptidoglycan layer is thinner compared to Gram-positive bacteria.
• They have an additional outer membrane that provides extra protection.
• Lipopolysaccharides in the outer membrane can trigger immune responses.

peptidoglycan

Peptidoglycan is a crucial component of bacterial cell walls, serving as a robust and vital structure for both Gram-positive and Gram-negative bacteria. It is composed of sugar chains cross-linked by peptides, forming a mesh-like layer that provides strength and rigidity to the cell wall.
In Gram-positive bacteria, the peptidoglycan layer is much thicker, contributing to their robust structure. This thick layer can be up to 90% of the cell wall composition in some Gram-positive bacteria.
Conversely, in Gram-negative bacteria, the peptidoglycan forms a thinner layer, which is part of a more complex multi-layered structure due to the presence of an outer membrane.

• Composed of sugars and amino acids.
• Forms a mesh-like structure crucial for cell wall integrity.
• Thicker in Gram-positive bacteria than in Gram-negative bacteria.

bacterial cell wall structure

Understanding the structure of bacterial cell walls is essential for grasping how bacteria survive, thrive, and resist treatment. The bacterial cell wall provides essential support, protecting them from environmental stress and maintaining their shape.
There are two major classes based on their staining characteristics, identified via the Gram staining method: Gram-positive and Gram-negative.
Gram-positive bacteria have thick cell walls primarily made of peptidoglycan, which helps them retain the crystal violet stain used in the Gram staining procedure.
Gram-negative bacteria, however, do not retain this stain and require a counterstain (usually safranin) because their thinner peptidoglycan layer is shielded by the outer membrane.

• A critical feature that differentiates Gram-positive and Gram-negative bacteria.
• Gram-positive bacteria have a thick peptidoglycan wall.
• Gram-negative bacteria have a thin peptidoglycan wall and an outer membrane.