Bacteria Lecture 4: Glycocalyx and Cell Membrane Structure

1. Bacteria Lecture 4

2. (Glycocalyx)

3. Shapes of bacteria Cocci - spherical Bacilli - rod Spiral - twisted rod, spirochete Coccobacilli

5. Cell Membrane Structure • Phospholipid bilayer with embedded proteins • Functions in: • Prevents leakage of cytoplasmic constituents out of the cell. • Prevents foreign things from getting in (for the most part). • Site of many proteins that transport things into and out of the, cell nutrient processing and synthesis. • Escherichia coli has >200 membrane proteins. • Some of these proteins allow a bacterium to sense its surrounding environments(e.g., as in chemotaxis).

6. flagella • Rotates 360o • Made of Flagellin protein • 1-2 or many distributed over entire cell • Functions in motility

7. Flagellar arrangements monotrichous – single flagellum at one end lophotrichous – small bunches arising from one end of cell amphitrichous – flagella at both ends of cell peritrichous – flagella dispersed over surface of cell, slowest

9. Axial filaments • Spiral cells that move by means of an axial filament (endoflagellum) are called spirochetes. • Axial filaments are similar to flagella, except that they wrap around the cell. • Motility

11. Pili (fimbrae) • Rigid tubular structure made of pilin protein • Found only in Gram negative cells • Functions • adhesion • joins bacterial cells for DNA transfer (conjugation)

12. Conjugation

13. Glycocalyx • Coating of molecules external to the cell wall, made of sugars and/or proteins • 2 types • capsule - highly organized, tightly attached • slime layer - loosely organized and attached • functions • inhibits killing by white blood cells (Phagocyctosis) • attachment

14. 2 Types of Glycocalyx

15. Fig 4.10

16. Peptidoglycan (cell wall) • unique macromolecule composed of a repeating framework of long glycan chains cross-linked by short peptide fragments • provides strong, flexible support to keep bacteria from bursting or collapsing because of changes in osmotic pressure

18. Peptidoglycan

19. 4 groups based on cell wall • Gram positive cells • Gram negative cells • Bacteria without cell walls • Bacteria with chemically unique cell walls

20. Gram positive Gram negative Thick Thin

21. Gram positive cell wall • Consists of • a thick, homogenous sheath of peptidoglycan 20-80 nm thick • tightly bound acidic polysaccharides, including teichoic acid and lipoteichoic acid

22. LPS Gram negative cell wall • Consists of • an outer membrane containing lipopolysaccharide (LPS) • thin shell of peptidoglycan • periplasmic space (Endotoxin)

24. Glycocalyx

25. Chromosome Single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell. DNA is tightly coiled around a protein, aggregated in a dense area called the nucleoid

26. Plasmid Small circular, double-stranded DNA. Free or integrated into the chromosome. Duplicated and passed on to offspring. Not essential to bacterial growth & metabolism. May encode antibiotic resistance, tolerance to toxic metals, enzymes & toxins. Used in genetic engineering- readily manipulated & transferred from cell to cell. Each bacterium may have more than one plasmid

27. Ribosomes • made of 60% ribosomal RNA & 40% protein. • consist of 2 subunits: large & small. • procaryotic differ from eucaryotic ribosomes in size & number of proteins. • site of protein synthesis. • All cells have ribosomes.

28. Ribosomes

29. Inclusions, granules intracellular storage bodies. vary in size, number & content. bacterial cell can use them when environmental sources are depleted. Examples: glycogen, poly-b-hydroxybutyrate, gas vesicles for floating, sulfur and polyphosphate granules.

30. Endospores Resting, dormant cells, metabolically inactive produced by some Gram positive bacteria : Clostridium, Bacillus & Sporosarcina. Have a 2-phase life cycle – vegetative cell & an endospore. sporulation -formation of endospores germination- return to vegetative growth . Hardiest of all life forms. Withstand extremes in heat, drying, freezing, radiation & chemicals not a means of reproduction. Resistance linked to high levels of calcium dipicolinic acid , “thick coat” Pressurized steam at 120oC for 20-30 minutes will destroy spores.

31. Endospores

32. Rickettsias Prokaryoteswithunusualcharacteristics Mycoplasmas - naturally lack a cell wall - obligate intracellular pathogens Chlamydias - obligate intracellular parasites.

33. Archaea: the other prokaryotes • Constitute third Domain Archaea • Contain unique genetic sequences in their rRNA • Have unique membrane lipids & cell wall construction • Live in the most extreme habitats in nature, extremophiles • Adapted to heat salt acid pH, pressure & atmosphere • Includes: methane producers, hyperthermophiles, extreme halophiles, and sulfur reducers

34. Bacterial identification • Macroscopic morphology – colony appearance • Microscopic morphology • Physiological / biochemical characteristics • Serological analysis • Genetic & molecular analysis

35. Eukaryotic cells

36. Eukaryotes • DNA in nucleus, surrounded by membrane • DNA in several chromosomes • Other organelles include endoplasmic reticulum, Golgi, lysosomes, mitochondria, chloroplasts • Cell walls chemically simple (none in animal cells) • 10-100 um in diameter

37. 3 Eukaryotic cells

38. Flagella • long, sheathed cylinder containing microtubules in a 9+2 arrangement • covered by an extension of the cell membrane • 10X thicker than procaryotic flagella • function in motility • similar in overall structure to flagella, but shorter and more numerous • found only on a single group of protozoa and certain animal cells • function in motility, feeding & filtering Cilia

39. Cell wall • rigid & provide structural support & shape • fungi have thick inner layer of polysaccharide fibers composed of chitin & a thin layer of mixed glycans • Algae – varies in chemical composition; substances commonly found include cellulose, pectin, mannans, silicon dioxide, & calcium carbonate

40. Transport process

41. Lysosomes • vesicles containing enzymes • involved in intracellular digestion of food particles & in protection against invading microbes

42. Mitochondria • Cristae hold the enzymes & electron carriers of areobic respiration • Divide independently of cell • Contain DNA and prokaryotic ribosomes • Function in energy production