Cell Structure

1. Cell Structure Chapter 3 (Part I)

2. Morphology of Prokaryotic Cells Prokaryotes exhibit a variety of shapes Most common Coccus Spherical Bacillus Rod or cylinder shaped Cell shape not to be confused with Bacillus genus

3. Other shapes Coccobacillus Short round rod Vibrio Curved rod Spirillum Spiral shaped Spirochete Helical shape Pleomorphic Bacteria able to vary shape

4. Pairs or chains of cells Pairs = diplo Example: Neisseria gonorrhoeae Chains = strepto Example: Streptococcus pyogenes

5. Clusters of cells Clusters = Staphylo Example: Staphylococcus aureus

6. Bacteria form multicellular associations myxobacteria These organisms form a swarm of cells Allows for the release of enzymes which degrade organic material biofilms �A biofilm can be defined as an aggregation of bacteria, algae, fungi and protozoa enclosed in a matrix consisting of a mixture of polymeric compounds, primarily polysaccharides, generally referred to as extracellular polymeric substance (EPS).� Vu et al., 2009. Organisms in biofilms are frequently resistant to antibiotics

7. Structural Features of Bacteria Cytoplasmic membrane Thin fluid mosaic structure Surrounds cytoplasm of cell Defines boundary Serves as a semi permeable barrier

8. Structure is a phospholipid bilayer with embedded proteins

9. Membrane is embedded with numerous proteins Numerous proteins are present Proteins function as receptors and transport gates Provides mechanism to sense surroundings Proteins are not stationary (fluid mosaic model)

10. Cell Wall Bacterial cell wall Rigid structure External to- and surrounds cytoplasmic membrane Determines shape of bacteria Prevents cell from bursting (physical strength) Unique chemical structure Distinguishes Gram-positive cells from Gram-negative cells

11. Rigidity: peptidoglycan (PTG) Compound found only in bacteria Basic structure of peptidoglycan: Alternating series of two subunits N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) Joined subunits form glycan chain Glycan chains held together by string of four amino acids (tetrapeptide chain)

12. Peptidoglycan Structure

13. Gram positive cell wall Relatively thick layer of PTG As many as 30, regardless of thickness, PTG is permeable to numerous substances Teichoic acid component of PTG

14. Gram-negative cell wall More complex than G-positive cell walls Contain thin layer of PTG PTG sandwiched between outer membrane and cytoplasmic membrane Region between outer membrane and cytoplasmic membrane is called Periplasm Lipoproteins link O.M. to PTG

15. Outer membrane Constructed of lipid bilayer Much like cytoplasmic membrane but outer leaflet made of lipopolysaccharides not phospholipids Outer membrane also called the lipopolysaccharide LPS layer LPS LPS severs as barrier to a variety of molecules However, small molecules or ions pass through channels called porins Portions of LPS are medically important O-specific polysaccharide side chain Lipid A

16. O-specific polysaccharide side chain Directed away from membrane Used to identify certain species or strains E. coli O157:H7 refers to specific O-side chain Lipid A Portion that anchors LPS molecule in lipid bilayer

17. Periplasm Region between C.M. and O.M. Filled with gel-like fluid (periplasm) In Gram negative bacteria, the periplasm contains all secreted proteins unless they contain signals that allow them to be specifically translocated across the O.M. Tremendous biological activity occurs in the periplasmic space