The outer membrane is made of lipopolysaccharide and porins, and they have more periplasmic space. The function of the S layer is not yet known.Gram-negative bacteria contain low peptidoglycan content (10-20%) and high lipid content (20-30%). It is also the only layer observed surrounding the cytoplasmic membrane. This layer occurs outside the wall of gram-positive bacteria and is external to the outer membrane of gram-negative bacteria. In addition to these layers, some bacteria have a crystalline protein layer surrounding the bacteria cell. In some cases, they act as traps for restricting the flow of substrates away from the cell. In some cases, they act as traps for nutrients. These external layers may protect the bacterium against dehydration and loss of nutrition. Although capsules and slime layer are similar in composition a distinction can be made between them.Īlthough both capsule and most slimy layers are composed of polysaccharides slimy layers are not as tightly bound to the cell as a capsule. Thus, having a capsule is the major factor in determining the pathogenicity of a bacterium. Phagocytes engulfs a large particle to form an internal part known as a phagosome) by various protozoa and human white blood cells. The capsule protects the bacteria against phagocytosis (phagocytosis definition – the process by which certain cells i.e. In contrast, some bacteria have a cell wall composed of glutamic acid. It often is composed of polysaccharides attached externally to the cell wall. The chemical composition of the capsule varies among the species of the bacteria. Some bacteria form a protective layer called a capsule. This general term includes the complex polysaccharides or protein and includes capsules, slime layer, and S layers. Collectively these structures are called the glycocalyx. Various external layers may surround the bacterial cell wall, playing various roles, including protection of the cell. Gram Negative Bacteria Examples Bacterial Capsules, Slime Layer, and S Layers What is Glycocalyx? Here we are discussing some of the gram-positive and gram-negative bacteria examples as follows: Gram Positive Bacteria Examples List Of Gram Positive And Gram Negative Bacteria These hydrolytic enzymes function in the periplasm and break down large molecules into smaller ones on their way to be used to produce ATP and cellular constituents. Hydrolytic (Hydro- water, lytic- break down) enzymes are generally catabolic enzymes that break the chemical bond between atoms of large molecules in the presence of water The chemoreceptors bind with substances and direct the cell movement towards or away from these substances. The binding proteins facilitate the transport of substances to carriers into the cell by delivering substances to carriers that are bound to the cytoplasm. Moreover, many proteins are found in this region, which include binding proteins, chemoreceptors, and enzymes including those involved in the oxidation-reduction process. This is an important region in gram-negative bacteria where diverse reactions occur, including oxidation-reduction reaction, osmotic regulation, solute transport, protein secretion, and hydrolytic activities. The region between the cytoplasm and outer membrane is known as periplasm (also called periplasmic space or periplasmic gel). Hydrophilic and hydrophobic molecules can diffuse through the outer membrane but the cytoplasmic membrane excludes almost all hydrophilic substances except water. The porins usually occur in aggregates of three and form cross-membrane channels through which some molecules can diffuse. The permeability of the outer membrane to the nutrients is due to the outer membrane proteins (Omp), collectively called porins. Teichuronic acids are polysaccharides chains of uronic acids and N-acetylglucosamine, which fulfill the cell requirements for the acidic, anionic polysaccharides in the cell wall.įunctionally, the outer membrane of the gram-negative bacterial cell is a course molecular sieve. This enables them to conserve phosphate that is essential for ATP, DNA, and other cellular components. When phosphate concentration is low, gram-positive bacteria replace the phosphate-rich teichoic acids of the cell wall with teichuronic acids. Teichoic acids also bind cations such as Ca2+ and Mg2+ and act as a receptor site for some viruses. This low pH prevents autolysins from degrading the cell wall. Teichoic acids can bind protons, thereby maintaining the cell wall at a relatively low pH. The teichoic acid is bonded to the peptidoglycan, making them an integral part of the gram-positive cell wall structure. Teichoic acids contain carbohydrates such as glucose, phosphate, and alcohol (either glycerol or ribitol). The cell walls of most gram-positive bacteria also have teichoic acids, which are acidic anionic polysaccharides.
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