1 Bacterial Cell Structure (continued) You are here.

2 Peptidoglycan structure

3 Bacteria and Osmotic pressure Bacteria typically face hypotonic environments –Insides of bacteria filled with proteins, salts, etc. –Water wants to rush in, explode cell. Peptidoglycan provides support –Limits expansion of cell membrane –Growth of bacteria and mechanism of penicillin Bacteria need other protection from hypertonic situations –Water leaves the cell; cell membrane shrinks –Lack of water causes precipitation of molecules, death

4 Effect of osmotic pressure on cells Hypotonic: water rushes in; PG prevents cell rupture. Hypertonic: water leaves cell, membrane pulls away from cell wall. In this example, the ENVIRONMENT relative to the inside of the cell.

5 Cell Wall Exceptions Mycobacterium and relatives (Gram + cells) –Wall contains lots of waxy mycolic acids –Attached covalently to PG Mycoplasma: no cell wall –Parasites of animals, little osmotic stress Archaea, the 3 rd domain –Pseudomurein and other chemically different wall materials (murein another name for PG)

6 Gram negative cell wall

7 Outer membrane Lipid bilayer membrane –Inner and outer leaflets Inner leaflet made of phospholipids; outer leaflet is made of lipopolysaccharide (LPS) LPS = endotoxin –Proteins for transport of substances Porins: tri-subunit, transmembrane proteins –Barrier to diffusion of various substances Lipoprotein: anchors outer membrane to PG

8 Structure of LPS cell_envelope.htm extends from cell surface. contains odd sugars e.g. KDO. Gln-P and fatty acids take the place of phospholipids.

9 Periplasmic Space theory.html

10 Periplasm The periplasm is the “stuff” in that space, present in Gram + bacteria also. –A hydrated gel including the PG –Binding proteins that aid in transport –Hydrolytic enzymes for breaking down large molecules –Chemoreceptor proteins that help direct swimming –Enzymes for synthesizing PG, OM

11 Glycocalyx: capsules and slime layers resources/visbulk.asp capsule cell “Sugar covering”: capsules are firmly attached, slime layers are loose. Multiple advantages to cells: prevent dehydration absorb nutrients protection from predators, WBCs protection from biocides (as part of biofilms) attachment to surfaces and site of attachment by others. S-layers are highly structured protein layers that function like capsules

12 Fimbriae and pili oralenv/images/sex1.jpg Both are appendages made of protein Singular: fimbria, pilus Both used for attachment Fimbriae: to surfaces (incl. host cells) and other bacteria. Pili: to other bacteria for exchanging DNA (“sex”).

13 Flagella tk/ce/flagella-s.gif introduction/bacteria.html Protein appendages used for locomotion. Made of subunits Rotate like propellers. Different from eukaryotic flagella. Arrangements on cells: polar, lophotrichous peritrichous.