Unveiling Prokaryotic Cell Structures and Functions

1. Bacterial Form and Function • Microbiology- Ch. 4 pp 87-101

2. Structure of a Prokaryotic Cell

3. Appendages- flagella, pili, fimbrae Cell envelope- glycocalyx, cell wall , cell membrane Cytoplasm- ribosomes, granules, nucleoid/chromosome. Prokaryote Structures:

4. Bacterial Appendages: • Pili (pl), pilus (s) • Only found in gram negative bacteria • hollow, hairlike structures of protein larger and more sparse than fimbriae. • allow bacteria to attach to other cells. • sex pilus, - transfer from one bacterial cell to another- conjugation. • fimbriae (pl) fimbria (s) • Adhesion to cells and surfaces • Responsible for biofilms. • Pathogenesis of gonococcus and E.coli • Flagella (pl), flagellum(s) • Motility- • long appendages which rotate by means of a "motor" located just under the cytoplasmic membrane. • Bacteria may have one, a few, or many flagella in different positions on the cell. • All spirilla, half of bacilli, rare cocci • Advantages- chemotaxis-positive and negative.

5. Flagella vary in number and arrangement. Polar arrangment- Monotrichious- 1 flagellum at one end Fastest; Pseudomonas -example Lophotrichious- tuft at one end Amphitrichious- bipolar Peritrichious- Multiple flagella; randomly dispersed around the bacterial cell E.coli -example Motility-

6. Structure of flagellaallows for 360 degree filament rotation

7. Flagellar arrangements

9. Detection of Motility • Stab line in semisolid motility agar growth out from the streak line indicates motility. A= motile; B=nonmotile • Motility plate • Hanging drop- from actively growing culture 18-24 hrs old. directional movement vs. “brownian movement

10. Bacterial Surface Structure-cell envelopeBacteria have some or all of the following structures: • Glycocalyx- capsule or slime layer • layer of polysaccharide (sometimes proteins) • Different composition in certain bacteria- • Streptococcus pneumoniae- capsule- tighter • Slime layer- looser, washes off • protects the bacterial cell from phagocytosis • associated with pathogenic bacteria -Staphylococcus aureus. • Glycocalyx- colonize nonliving materials- plastics, catheters, medical devices. • Cell wall – • peptidoglycan (polysaccharides + protein), • Support and shape of a bacterial cell. The three primary shapes in bacteria are: • coccus (spherical), • bacillus (rod-shaped) • spirillum (spiral). • Mycoplasma are bacteria that have no cell wall and therefore have no definite shape.

13. 2. Cell wall – peptidoglycan (polysaccharides + protein) Repeating glycan chains (N acetyl glucosamine and N acetyl muramic acid) with crosslinked peptides. Support and shape of a bacterial cell. The three primary shapes in bacteria are: • coccus (spherical), • bacillus (rod-shaped) • spirillum (spiral). • Mycoplasma are bacteria that have no cell wall and therefore have no definite shape.

15. Differences in Cell Wall Structure • Basis of Gram Stain Reaction • Hans Christian Gram- 1884 • Differential Stain • Gram Positive vs Gram Negative Cells • Gram Positive Cells- • Thick peptidoglycan layer with embedded teichoic acids • Gram Negative Cells- • Thin peptidoglycan layer, outer membrane of lipopolysaccharide.

16. Gram Stain Reaction • Hans Christian Gram- 1880s • Divides bacteria into 2 main groups- • Gram positive • Gram negative • Also- gram variable • Gram nonreactive • Gram positive bacteria • many layers of peptidoglycan and teichoic acids. • Form a crystal violet-iodine-teichoic acid complex • Large complex,difficult to decolorize

18. Gram negative cells • Very thin peptidoglycan • No teichoic acids • Alcohol decolorizer readily removes the crystal violet. • Alcohol also dissolves the lipopolysaccharide of the cell wall. • Gram variable cells • Some cells retain crystal violet; some decolorize and take up the safranin • 4 factors- • Genetics- variable amount of teichoic acid. • Age of culture- older cultures have variable amount of teichoic acid • Growth medium- necessary nutrients not available • Technique- • smear not thin or evenly made. • Staining procedure not done correctly- decolorizer left on too long.

20. Gram nonreactive cells • Have peptidoglycan but have very waxy- thick lipids –waterproof, dyes cannot enter either. • Examples- Mycobacterium- tuberculosis and leprosy. • Alternative staining- acid fast stain-

21. Cell wall deficient formsFigure 4.17 • L- forms ( Lister Institute where discovered) • Bacteria loses cell wall during the life cycle • Result of a mutation in cell wall forming genes • Induced by treating with lysozyme or penicillin which disrupts the cell wall • Protoplast- • G + bacterium with no c. wall, only a c. membrane • Fragile, easily lysed • Spheroplast- • G – bacterium loses peptidoglycan, but has outer membrane • Less fragile but weakened.

22. Surface structures continued: • Outer membrane • This lipid bilayer is found in Gram negative bacteria and is the source of lipopolysaccharide (LPS) in these bacteria • LPS is toxic and turns on the immune system. • Not found in Gram positive bacteria.

23. Cell membrane • Located just beneath cell wall • Very thin • Lipid bilayer, similar to the plasma membrane of other cells. Transport of ions, nutrients and waste across the membrane • Typical • 30-40% phospholipids • 60-70% proteins • Exceptions- • Mycoplasma- sterols • Archaea- unique branched hydrocarbons

25. Mesosome Extension of cell membrane • Folding into cytoplasm – internal pouch • Increases surface area. • Gram-positive bacteria-prominent • Gram negative bacteria- smaller,harder to see. • Functions- • Cell wall synthesis • Guides duplicated chromosomes into the daughter cells in cell division.

26. Photosynthetic Prokaryotes • Cyannobacterium- dense stacks of internal membranes with photosynthetic pigments.

27. Functions of Cell Membrane • Carries out functions normally carried out by eukaryote organelles. • Site for energy functions • Nutrient processing • Synthesis • Transport of nutrients and waste • Selectively permeable • Most enzymes of respiration and ATP synthesis • Enzyme synthesis of structural macromolecules • Cell envelope and appendages • Secretion of toxins and enzymes into environment.

28. Cell cytoplasm • Encased by cell membrane • Dense, gelatinous • Prominent site for biochemical and synthetic activities • 70-80% water- solvent • Mixture of nutrients- sugar, amino acids, salts • Building blacks for cell synthesis and energy

29. Bacterial chromosome • Singular circular strand of DNA • Aggregated in a dense area- nucleiod • Long molecule of DNA tightly coiled around protein molecules. • Plasmids- • Nonessential pieces of DNA • Often confer protection- resistance to drugs • Tiny, circular • Free or integrated • Duplicate and are passed on to offspring • Used in genetic engineering

30. Ribosomes • Site of protein synthesis • Thousands • Occurs in chains –polysomes • 70S • 2 smaller subunits • 30S and 50S

32. Inclusions • If nutrients abundant- stored intracellularly • Granules- • Crystals of inorganic compounds not enclosed by membranes • Sulfur granules- photosynthetic • Polyphosphate- corynebacterium • Metachromatic- Mycobacterium

33. Bacterial Internal Structures • Endospores • inert, resting, cells produced by some G+ genera: Clostridium, Bacillus and Sporosarcina • have a 2-phase life cycle: • vegetative cell – metabolically active and growing • endospore – when exposed to adverse environmental conditions; capable of high resistance and very long-term survival • Features of spores- size, shape, location=identification • sporulation -formation of endospores • hardiest of all life forms • Forms inside a cell- functions in survival • not a means of reproduction • withstands extremes in heat, drying, freezing, radiation and chemicals • germination- return to vegetative growth

35. Endospores • Resistance linked to high levels of calcium and dipicolinic acid • Dehydrated, metabolically inactive • thick coat • Longevity verges on immortality - 25,250 million years. • Resistant to ordinary cleaning methods and boiling • Pressurized steam at 120oC for 20-30 minutes will destroy

36. Bacterial Shapes, Arrangements, and Sizes • Variety in shape, size, and arrangement but typically described by one of three basic shapes: • coccus - spherical • bacillus – rod • coccobacillus – very short and plump • vibrio – gently curved • spirillum - helical, comma, twisted rod, • spirochete – spring-like

38. Bacterial Shapes, Arrangements, and Sizes • Arrangement of cells is dependent on pattern of division and how cells remain attached after division: • cocci: • singles • diplococci – in pairs • tetrads – groups of four • irregular clusters • chains • cubical packets • bacilli: • chains • palisades