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1 Bacterial Cell Structure (continued) You are here.

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1 1 Bacterial Cell Structure (continued) You are here.

2 2 Peptidoglycan structure Bacteria typically face hypotonic environments Peptidoglycan provides support, Limits expansion of cell membrane Bacteria need other protection from hypertonic situations

3 3 Gram negative cell wall

4 4 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: transmembrane proteins –Barrier to diffusion of various substances Lipoprotein: anchors outer membrane to PG

5 5 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.

6 6 Periplasmic Space theory.html

7 7 Periplasmic space: A lot like cytoplasm, with –Peptidoglycan layer –Proteins that aid in transport –Proteins that break down molecules –Proteins that help in synthesis.

8 8 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

9 9 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”).

10 10 Flagella tk/ce/flagella-s.gif introduction/bacteria.html Flagella: protein appendages for swimming through liquid or across wet surfaces. Rotate like propellers. Different from eukaryotic flagella. Arrangements on cells: polar, Lophotrichous, amphitrichous, peritrichous.

11 11 Prokaryotic vs. eukaryotic flagella gifs/flagella.gif BIOL/Flagella.jpg Prokaryotic flagella : Made of protein subunits Protrude through cell wall and cell membrane. Stiff, twirl like a propeller Eukaryotic flagella : A bundle (9+2) of microtubules (made of protein) Covered by cell membrane Whipping action

12 12 Chemotaxis Bacteria change how they move in response to chemicals Bacteria move toward attractants (e.g. nutrients). Bacteria move away from repellants. In this figure, bacteria use up nutrients in the agar, then move outward to where more nutrients are, producing rings of growth.

13 13 Runs and Tumbles: bacteria find their way

14 14 Spirochetes have internal flagella Axial filament: a bundle of internal flagella –Between cell membrane and outer membrane in spirochetes –Filament rotates, bacterium corkscrews through medium Some bacteria move without flagella Gliding –No visible structures, requires solid surface –Slime usually involved.

15 15 Axial filaments imgrefurl= pF7UJ:&tbnh=90&tbnw=119&start=1&prev=/images%3Fq%3Daxial%2Bfilament%2Bbacteria%26hl%3Den%26lr%3D%26sa%3DG

16 16 Gliding Motility Movement on a solid surface. No visible organelles of locomotion. Cells produce, move in slime trails. Unrelated organism glide: myxobacteria, flavobacteria, cyanobacteria; appear to glide by different mechanisms. Cells glide in groups, singly, and can reverse directions. myxobacteria/trails.jpg

17 17 From the membrane in: the bacterial cytoplasm Cytoplasm is a gel made of water, salts, LMW molecules, and lots of proteins. DNA = nucleoid, w/ proteins Plasmids = small circular DNA Ribosomes: site of protein synthesis. Cytoplasm may also contain inclusions, gas vacuoles, extended membrane systems, or magnetosomes. But generally NO membrane-bound organelles.

18 18 Inclusions and granules Storage molecules found as small bodies within cytoplasm. Can be organic (e.g. PHB or glycogen) or inorganic (Sulfur, polyphosphate. –PHB, a type of PHA, degradable plastic (polyester); glycogen, a polymer of glucose. –Sulfur, a metabolic by-product; polyphosphate, polymer of PO 4 phosphate_removal.htm

19 19 Magnetosomes mtbphoto.html Membrane coated pieces of magnetite, assist bacteria in moving to microaerophilic environments. An organelle? North is down. Magnetospirillum magnetotacticum

20 20 How things get in (and out) of cells Eukaryotic cells –Have transport proteins in membrane –Have a cytoskeleton made of microtubules Allows for receptor mediated endocytosis, phagotcytosis, etc. Cell membrane pinches in, creates vesicle Prokaryotic cells –Have very little cytoskeleton –Can NOT carry out endocytosis –Entry of materials into cell by diffusion or transport processes ONLY.

21 21 Illustrations: entry into cells Both prokaryotes and eukaryotes. Only eukaryotes.

22 22 How molecules get through the membrane Small molecules like gases can diffuse through the bilayer. Larger or more hydrophilic molecules require transport proteins. Active transport requires metabolic energy.

23 23 Review of eukaryotic cells Mitochondrion Plasmalemma (cell membrane) nucleus, ribosomes lysozome endoplasmic reticulum golgi body science/cell_biology.html

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