Gram-positive

Definition

Gram-positive bacteria are a group of prokaryotic cells that stain purple or dark blue when subjected to the Gram staining procedure. This characteristic is due to the unique structure of their cell wall, which is thick and composed primarily of peptidoglycan, a rigid polymer that provides structural support and protection to the cell.

5 Must Know Facts For Your Next Test

1. Gram-positive bacteria have a thick, multilayered cell wall composed primarily of peptidoglycan, which accounts for 30-90% of the cell wall's dry weight.
2. The peptidoglycan layer in Gram-positive bacteria is much thicker than in Gram-negative bacteria, typically ranging from 20 to 80 nanometers in thickness.
3. Gram-positive bacteria often have additional cell wall components, such as teichoic acids and lipoteichoic acids, which contribute to the overall structure and function of the cell wall.
4. The thick peptidoglycan layer in Gram-positive bacteria provides them with increased resistance to physical and chemical stresses, including certain antibiotics that target the cell wall.
5. The Gram staining procedure relies on the ability of Gram-positive bacteria to retain the crystal violet dye, while Gram-negative bacteria are unable to do so, leading to the characteristic purple or blue staining of Gram-positive cells.

Review Questions

• Describe the key structural differences between Gram-positive and Gram-negative bacterial cell walls.
  • The primary structural difference between Gram-positive and Gram-negative bacterial cell walls is the composition and thickness of the peptidoglycan layer. Gram-positive bacteria have a thick, multilayered peptidoglycan cell wall, which accounts for 30-90% of the cell wall's dry weight and can range from 20 to 80 nanometers in thickness. In contrast, Gram-negative bacteria have a much thinner peptidoglycan layer, with an additional outer membrane that is not present in Gram-positive cells. This structural difference is the basis for the Gram staining procedure, where Gram-positive cells retain the crystal violet dye and appear purple or blue, while Gram-negative cells do not.
• Explain how the Gram-positive cell wall structure contributes to the bacteria's resistance to certain antibiotics.
  • The thick peptidoglycan layer in Gram-positive bacterial cell walls provides increased resistance to physical and chemical stresses, including certain antibiotics that target the cell wall. The multilayered peptidoglycan structure acts as a barrier, making it more difficult for antibiotics to penetrate and disrupt the cell wall. This increased resistance can make Gram-positive bacteria more challenging to treat with cell wall-targeting antibiotics, as the drugs may have a harder time reaching their intended targets within the bacterial cells.
• Analyze the role of the Gram staining procedure in the identification and classification of prokaryotic cells.
  • The Gram staining procedure is a fundamental technique used to classify and identify prokaryotic cells based on their cell wall structure. By subjecting bacterial cells to a series of staining steps, Gram-positive cells retain the crystal violet dye and appear purple or blue, while Gram-negative cells do not. This distinction is directly related to the composition and thickness of the peptidoglycan layer in the cell wall. The Gram staining result is a crucial characteristic used in the initial identification and classification of bacteria, as it provides important information about the cell wall structure and can inform subsequent diagnostic and treatment decisions.

Related terms

Gram-negative:

Gram-negative bacteria are a group of prokaryotic cells that stain pink or red when subjected to the Gram staining procedure. Their cell wall structure differs from Gram-positive bacteria, with a thinner peptidoglycan layer and an additional outer membrane.

Peptidoglycan:

Peptidoglycan is a structural component of the bacterial cell wall, consisting of sugar molecules (N-acetylglucosamine and N-acetylmuramic acid) cross-linked by short peptide chains. It provides rigidity and shape to the cell.

Cell Wall: The cell wall is a rigid structure surrounding the cell membrane of prokaryotic cells, providing protection, shape, and structural support. It is composed of various materials, such as peptidoglycan, teichoic acids, and other polymers.