Bacterial cell Parts and Functions
The bacterial cell surface (or envelope) can vary considerably in its structure, and it plays a central role in the properties and capabilities of the cell. The one feature present in all cells is the cytoplasmic , which separates the inside of the cell from its external environment, regulates the flow of nutrients, maintains the proper intracellular milieu, and prevents the loss of the cell’s contents. The cytoplasmic membrane carries out many necessary cellular functions, including energy generation, protein , segregation, and efficient active transport of nutrients. It is a typical unit membrane composed of proteins and lipids, basically similar to the membrane that surrounds all eukaryotic cells. It appears in electron micrographs as a triple-layered structure of lipids and proteins that completely surround the cytoplasm.
Lying outside of this membrane is a rigid that determines the shape of the bacterial cell. The wall is made of a huge molecule called peptidoglycan (or murein). In gram-positive bacteria the peptidoglycan forms a thick meshlike layer that retains the blue dye of the Gram stain by trapping it in the cell. In contrast, in gram-negative bacteria the peptidoglycan layer is very thin (only one or two molecules deep), and the blue dye is easily washed out of the cell.
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microbiology: Bacteria (eubacteria and archaea)
Microbiology came into being largely through studies of bacteria. The experiments of Louis Pasteur in France, Robert Koch in Germany, and others in the late 1800s established the importance of microbes to humans. As stated in the Historical background section, the research of these scientists provided proof for the germ theory of disease and the germ theory of fermentation. It was in their...
READ MOREPeptidoglycan occurs only in the Bacteria (except for those without a cell wall, such as Mycoplasma). Peptidoglycan is a long-chain of two repeating sugars (n-acetylglucosamine and n-acetyl muramic acid), in which adjacent sugar chains are linked to one another by peptide bridges that confer rigid stability. The nature of the peptide bridges differs considerably between species of bacteria but in general consists of four : l- linked to d-, linked to either diaminopimelic acid in gram-negative bacteria or l-, l-ornithine, or diaminopimelic acid in gram-positive bacteria, which is finally linked to d-alanine. In gram-negative bacteria the peptide bridges connect the d-alanine on one chain to the diaminopimelic acid on another chain. In gram-positive bacteria there can be an additional peptide chain that extends the reach of the cross-link; for example, there is an additional bridge of five in Staphylococcus aureus.
Peptidoglycan synthesis is the target of many useful , including the β-lactam antibiotics (e.g., ) that block the cross-linking of the peptide bridges. Some of the proteins that animals synthesize as natural antibacterial defense factors attack the cell walls of bacteria. For example, an enzyme called splits the sugar chains that are the backbone of peptidoglycan molecules. The action of any of these agents weakens the cell wall and disrupts the bacterium.
