Chapter 4

1. Chapter 4 Prokaryotic organisms

2. Prokaryotic cell • Includes bacteria and archaea • Thousands of species of bacteria differ by morphology (shape), chemical composition, nutritional requirements, biochemical activities, and sources of energy • Bacteria divide by binary fission (asexual reproduction)

3. Size, shape, and arrangement • Most bacteria range in size between 0.2 micrometers (microns) to 2.0 microns • The basic shapes are cocci, bacilli, and spirilla • Cocci may occur in pairs (diplococci), in chains (streptococci), and in clusters (staphylococci) • Bacilli may appear as single rods, diplobacilli, streptobacilli, or coccobacilli

4. Other shapes • Spiral bacteria have one or more twists • Curved rods (comma shaped) are vibrios • Others called spirilla are corkscrew shaped and move with whip-like appendages called flagella • Spirochetes are helical and flexible and move by axial filaments • Most bacteria maintain a single shape and are monomorphic, but some may have more than one shape and are pleomorphic

5. Structures external to cell wall • Glycocalyx means sugar coat, and is a sticky, gelatinous polymer that is outside the cell wall • If the glycocalyx is firmly attached to cell wall and is organized it is called a capsule • If the glycocalyx is unorganized and loosely attached it is called a slime layer • Streptococcus pneumoniae, Haemophilus influenzae, Bacillus anthracis have them

6. Flagella • These are long, filamentous appendages that help bacteria move (motile) • No flagella is called atrichous • A single polar flagellum is monotrichous • A tuft of flagella at each end is amphitrichous • Two or more at one (or both) ends is lophotrichous • Flagella all over is peritrichous

8. Flagella • The flagellum has 3 basic parts: filament is the long, outermost region; a hook attaches to the filament; the basal body, which anchors the flagellum to the cell wall and plasma membrane • The basal body is a small central rod inserted into a series of rings • In gram negative bacteria, there are two pair of rings • In gram positive bacteria, only the inner pair is present

9. Motility • Bacteria have a ‘run and tumble’ movement thanks to flagella • A bacterium with flagella can move quickly toward or away from a stimulus • Bacteria moving toward chemical stimulus is positive chemotaxis • Bacteria moving away is negative chemotaxis • Moving in response to light is phototaxis

10. Axial Filaments • Spirochetes are unique in structure and motility • Treponema pallidium causes syphilis, Borrelia burgdorferi causes Lyme disease • Spirochetes move by axial filaments, which spiral around the cell and cause a corkscrew like movement

11. Fimbriae and Pili • Many gram negative bacteria contain shorter hairlike appendages called fimbriae and pili • These are used for attachment and transfer of DNA • Fimbriae help cell stick to surfaces (Neisseria gonorrhoeae) • Pili (sex pili or conjugation pili) help cells transfer DNA in conjugation

12. Cell Wall • Helps maintain shape of the cell • Keeps cell from rupturing • Contributes to ability to cause disease • Is the site of action of some antibiotics • Helps tell differences in major types of bacteria

13. Composition • Contains peptidoglycan which consists of repeating disaccharides attached by polypeptides that forms a lattice • Disaccharide portion has monosaccharides called N-acetyl glucosamine (NAG) and N-acetylmuramic acid (NAM) • Alternating NAG and NAM are linked to form a backbone, and adjacent rows are linked by polypeptides

14. Difference between gram positive and negative cells • Gram negative have an outer membrane • Gram positive cells do not have an outer membrane, so the peptidoglycan is exposed and more easily destroyed by antibiotics like penicillin

15. Gram negative vs. Gram positive • Gram positive cell wall has thick peptidoglycan • Gram negative has a thin layer • Gram positive cell has teichoic acids which help bind and regulate movement of cations in/out of the cells • Teichoic acids may also provide antigenic specificity which makes it easier to ID bacteria

16. Gram negative cells • Have thin layer of peptidoglycan and an outer membrane • The outer membrane (OM) has lipopolysaccharide (LPS), lipoprotein, and phospholipid • It has a negative charge which helps the bacteria avoid phagocytosis and complement (both are host defenses)

17. Gram negative OM • It also is a barrier to antibiotics, enzymes, etc. • Has porins (proteins) which allow passage of some material in and out • LPS component has an O polysaccharide portion and a lipid portion (lipid A) • The O polysaccharide is an antigen and is used to help ID the bacteria • The Lipid A is a toxin (endotoxin) that can cause fever and shock (endotoxin shock)

18. Atypical cells • Mycoplasma has no cell wall (causes walking pneumonia), but do have sterols to protect against rupture • Acid Fast Cell Walls- Mycobacterium and Nocardia have mycolic acid in cell wall, which causes these bacteria to clump and stick together. • Damage to cell wall by lysozyme causes either a spheroplast (gram negative) or a protoplast (gram positive)

19. Cell or Plasma Membrane • Encloses the cytoplasm • Made of phospholipids (bilayer), proteins, glycoprotein, glycolipid • Arrangement is phospholipid bilayer • Heads (hydrophilic), tails (hydrophobic) • Selective permeability • ATP production occurs here

20. Movement across membranes • Passive process-movement from high concentration to low without using ATP • Includes simple diffusion (alka seltzer example) • Facilitated diffusion-requires a protein transporter to allow movement across membrane • Osmosis-movement of water from greater water to less water

21. Osmosis • Movement produces osmotic pressure-this is the pressure needed to stop the flow of water across the membrane • 3 types of osmotic solutions: isotonic-equal solid; no change in cell when placed in this type of solution • Hypotonic=less solid, cell will swell • Hypertonic=greater solid; cell will shrink

22. Inside cell • Cytoplasm is 80% water and contains proteins, carbohydrates, lipids, inorganic ions, and contains the nuclear area, ribosomes, and inclusions • Nuclear area contains loop shaped DNA • May have pieces of DNA called plasmids that carry genes for resistance (resistance factors or R factors)

23. Inside cell continued • Ribosomes-sites of protein synthesis • Contained in eukaryotic cells too, but different because they are 80 S (Svedberg unit); 40 S + 60 S) • Prokaryotic ribosomes are 70 S (30 S + 50 S) • Inclusions are extra storage areas including gas vacuoles, sulfur granules, land lipid inclusions • Metachromatic granules -collectively known as volutin, represents a reserve of inorganic phosphate • Magnetosomes-inclusions of iron oxide found in some gram negatives that act like magnets

24. Endospores • Form in gram positive rods when essential nutrients are depleted • Endospores are highly durable and can survive extremes of heat, dehydration, and exposure to toxins and radiation • Begin sporulation when a key nutrient becomes scarce • Endospores may remain dormant for years, and will eventually ‘germinate’ and become a vegetative cell again

25. Shapes, review Shapes; cocci (spherical), bacilli (rods), vibrio (comma), spirochetes (spring), spirillum (helix) Arrangements: Staphylo (clusters), strepto (chains), mono (single), diplo (pairs), tetrads (4), sarcina (8), palisade (side by side like a picket fence) Pleomorphism-variable shapes like Corynebacterium