Bacterial cell wall
- 2. CELL WALL The cell wall is the outer most layer of the cell. In many cases the cell wall comes in direct contact with the environment. Function • Protection of the cell. • Maintains the shapes of the cell. • Maintains the osmotic integrity of the cell.
- 3. • Assist some cells in attaching to other cells or in eluding antimicrobial drugs. • Not present in animal cells, so can target cell wall of bacteria with antibiotics. • Providing attachment sites for bacteriophages. • Play an essential role in cell division. • Providing a rigid platform for surface appendages- flagella, fimbriae and pili.
- 5. Peptidoglycan • Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the cell membrane of most bacteria forming the cell wall. • The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N- acetylmuramic acid. • These subunits which are related to glucose in their structure are covalently joined to one another to form glycan chains.
- 6. • Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the peptidoglycan.
- 9. Gram Positive Cell wall • Usually thick, homogenous, composed mainly of peptidoglycan. • It accounts for 50-90% of the dry weight of the cell wall. • Contain large amount of teichoic acids (polymers of glycerol or ribitol joined by phosphate group).
- 11. Special components of Gram positive cell wall Teichoic acid
- 12. Teichoic acid • Teichoic acids are connected to either peptidoglycan or to plasma membrane lipids. • Absent in gram negative bacteria. Function of Teichoic Acid: . Antigenic determinant (receptor molecule for bacteriophages). . Participate in the supply of Mg to the cell by binding Mg++ . Regulate normal cell division. For most part, protein is not found as a constituent of the G+ cell wall except M protein on group streptococci.
- 13. Gram Negative Cell Wall • Multi layered and more complex than Gram positive cell walls. • Peptidoglycan of gram negative bacteria is thin and comprises only 10% or less of cell wall. • Outer membrane lies outside the thin peptidoglycan layer. • Most abundant protein is Braun’s lipoprotein.
- 15. Special components of Gram negative cell wall
- 16. Periplasm: • The region between the cytoplasmic membrane and the outer membrane is filled with a gel-like fluid called periplasm. • In gram negative bacteria, all secreted proteins are contained within the periplasm, unless they are specifically translocated across the outer membrane. • Periplasm is filled with the proteins that are involved in various cellular activities, including nutrient degradation and transport.
- 17. Outer membrane • Peptidoglycan layer is surrounded by outer membrane in the gram negative bacteria. • Its outside leaflet is made up of lipopolysaccharides, rather than phospholipids. • For this reason, the outer membrane is also called the lipopolysaccharide layer or LPS. • The outer membrane functions as a protective barrier and excludes many toxic compounds.
- 18. • Lipopolysaccharide molecule is extremely important from a medical stand point. • It consists of three parts, two of them are medically significant. 1. Lipid A…..embedded in membrane. 2. Core polysaccharide…..located on the surface of membrane. 3. O antigens….which are short polysaccharides extended out from core.
- 19. • Lipid A: The chemical makeup of lipid A molecule plays significant role in our body’s ability to recognize the presence of invading bacteria. • It is toxic in nature, as a result the LPS can act as an endotoxin, causing symptoms like fever, diarrhea and shock. • O-antigen: It is composed of carbohydrates, including glucose, galactose, mannose and some other sugars in varying combinations. • The O-antigens can react with their specific antibodies.