Gram-positive cell wall


Bacteria are microscopic organisms that can be classified into two major groups based on the structure of their cell wall: Gram-positive and Gram-negative. The cell wall is a rigid layer that surrounds the cell membrane and protects the bacterial cell from environmental stress and mechanical damage. The cell wall also determines the shape of the bacterial cell and provides attachment sites for various molecules and structures.

The Gram-positive cell wall is named after the Danish bacteriologist Hans Christian Gram, who developed a staining technique in 1884 to differentiate between different types of bacteria. The Gram stain involves applying a series of dyes to a bacterial smear and observing the color under a microscope. Gram-positive bacteria retain the primary dye (crystal violet) and appear purple, while Gram-negative bacteria lose the primary dye and take up the counterstain (safranin) and appear pink.

The reason for this difference in staining is the composition and thickness of the cell wall. The Gram-positive cell wall is thick (15–80 nm) and more homogenous than that of the thin (2 nm) Gram-negative cell wall. The Gram-positive cell wall contains large amount of peptidoglycan, a polymer of sugar and amino acids that forms a mesh-like layer that gives strength and rigidity to the cell wall. Peptidoglycan constitutes about 40–80% of the dry weight of the Gram-positive cell wall.

In addition to peptidoglycan, the Gram-positive cell wall contains other components that are unique to this group of bacteria. These include teichoic acids, teichuronic acids, polysaccharides, proteins, and lipids. These components account for up to 50% of the dry weight of the wall and 10% of the dry weight of the total cell. They play various roles in the structure, function, and interaction of the Gram-positive bacteria with their environment.

In this article, we will explore the composition and role of these components in more detail, starting with teichoic acids and their functions.