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Gram-positive bacteria have a thick layer of peptidoglycan within the cell wall, and Gram-negative bacteria have a thin layer of peptidoglycan. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope.
The cell wall of some Gram-positive bacteria can be completely dissolved by lysozymes which attack the bonds between N-acetylmuramic acid and N-acetylglucosamine. In other Gram-positive bacteria, such as Staphylococcus aureus, the walls are resistant to the action of lysozymes. [4] They have O-acetyl groups on carbon-6 of some muramic acid ...
The outer red layer in this diagram is the capsule, which is distinct from the cell envelope. This bacterium is gram-positive, as its cell envelope comprises a single cell membrane (orange) and a thick peptidoglycan-containing cell wall (purple). The bacterial capsule is a large structure common to many bacteria. [1]
Gram staining is a bacteriological laboratory technique [7] used to differentiate bacterial species into two large groups (gram-positive and gram-negative) based on the physical properties of their cell walls. [8][page needed] Gram staining can also be used to diagnose a fungal infection. [1]
The cell envelope comprises the inner cell membrane and the cell wall of a bacterium. In Gram-negative bacteria an outer membrane is also included. [1] This envelope is not present in the Mollicutes where the cell wall is absent. Bacterial cell envelopes fall into two major categories: a Gram-positive type which stains purple during Gram ...
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Peptidoglycan. Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like layer (sacculus) that surrounds the bacterial cytoplasmic membrane. [1] The sugar component consists of alternating residues of β- (1,4) linked N -acetylglucosamine (NAG) and N -acetylmuramic ...
The general secretion (Sec) involves secretion of unfolded proteins that first remain inside the cells. In Gram-negative bacteria, the secreted protein is sent to either the inner membrane or the periplasm. But in Gram-positive bacteria, the protein can stay in the cell or is mostly transported out of the bacteria using other secretion systems.