Microbiology Chapter 3: Cell Structure and Function

Universal Characteristics of Life:
- Growth: Increase in size.
- Reproduction: Increase in number.
- Responsiveness: Ability to react to environmental stimuli.
- Metabolism: Controlled chemical reactions within organisms.
Microbe Distribution:
- Bacteria, Archaea, Eukaryotes: Exhibit all four characteristics plus cellular structure.
- Viruses: Do not grow; host cells replicate the virus; show limited responsiveness to host cells; use host metabolism; lack cytoplasmic membranes or cellular structure.
Smallest Microbe: Mycoplasma is the smallest free-living microbe and is nonmotile.

Prokaryotes (Bacteria and Archaea):
- Lack a nucleus and membrane-bound organelles.
- Can read DNA and make protein simultaneously.
- Typically small: $\le 1.0\,\mu\text{m}$ in diameter.
Eukaryotes (Algae, Protozoa, Fungi, Animals, Plants):
- Have a nucleus and internal membrane-bound organelles.
- Larger and more complex: $10\text{--}100\,\mu\text{m}$ in diameter.
Case Study: Epulopiscium fishelsoni is a giant bacterium visible to the naked eye, initially mistaken for a eukaryote due to its size.

Glycocalyces: Gelatinous, sticky substances made of polysaccharides and/or polypeptides.
- Capsule: Firmly attached; organized units; prevents host recognition.
- Slime layer: Loosely attached; water-soluble; facilitates biofilm formation.
Flagella: Long structures for motility.
- Components: Filament, hook, and basal body (anchors to cell wall/membrane).
- Arrangements: Monotrichous, amphitrichous, lophotrichous, peritrichous.
- Endoflagella: Found in spirochetes; form an axial filament for corkscrew motion.
- Movement: Driven by rotation; involves "runs" (counterclockwise) and "tumbles" (clockwise) in response to stimuli (taxis).
Fimbriae and Pili:
- Fimbriae: Bristlelike; used for adherence and biofilms.
- Pili (Conjugation Pili): Longer than fimbriae; used to transfer DNA between cells.

Function: Provide shape and protection against osmotic forces.
Peptidoglycan: Composed of alternating sugars (NAG and NAM) and amino acid crossbridges.
Gram-Positive1 Cell Walls:
- Thick peptidoglycan layer.
- Contain teichoic acids and lipoteichoic acids.
- Appear purple after Gram staining.
- Acid-fast bacteria contain up to $60\%$ mycolic acid.
Gram-Negative Cell Walls:
- Thin peptidoglycan layer.
- Bilayer outer membrane containing phospholipids, proteins, and Lipopolysaccharide (LPS).
- Lipid A: Portion of LPS triggering fever, inflammation, and shock.
- Appear pink after Gram staining.

Structure: Phospholipid bilayer (Fluid Mosaic Model).
Transport Processes:
- Passive: Diffusion, Facilitated diffusion, and Osmosis (movement of water).
- Solutions: Isotonic, Hypertonic, and Hypotonic.
- Active: Requires ATP; Includes Uniport, Antiport, Symport (coupled), and Group Translocation (chemical modification of substance during transport).
Transported Substances: Oxygen, $CO_2$ (Diffusion); Glucose (Facilitated diffusion/Group translocation); $Na^+$ , $K^+$ , $Ca^{2+}$ , $H^+$ , $Cl^-$ (Active transport).

Cytosol: Liquid portion containing DNA in the nucleoid.
Inclusions: Reserve deposits of chemicals (e.g., PHB).
Endospores: Produced by Bacillus and Clostridium; highly resistant to heat, radiation, and chemicals; defensive strategy against limited nutrients.
Nonmembranous Organelles:
- Ribosomes: Sites of protein synthesis; $70\text{S}$ in prokaryotes.
- Cytoskeleton: Roles in cell division, shape, and DNA segregation.

External: Utilize hami (grappling-hook structures) for attachment; flagella grow from the base and are thinner than bacterial flagella.
Cell Walls: Lack peptidoglycan; made of specialized proteins or polysaccharides.
Membranes: Use ether linkages (rather than ester linkages found in bacteria).
Cytoplasm: $70\text{S}$ ribosomes, but genetic code and ribosomal proteins more closely resemble eukaryotes.

External: Glycocalyces (animal cells); Cell walls (plants: cellulose; fungi: chitin/glucomannan).
Flagella/Cilia: Shaft of tubulin in $9+2$ microtubule arrangement; undulate rather than rotate.
Organelles:
- Nucleus: Contains chromatin; surrounded by a double-membrane nuclear envelope with pores.
- Endoplasmic Reticulum (ER): Rough ER (protein synthesis/transport) and Smooth ER (lipid synthesis).
- Golgi Body: Packages molecules in secretory vesicles.
- Mitochondria: Produce ATP; contain their own $70\text{S}$ ribosomes and circular DNA.
- Chloroplasts: Light-harvesting; contain $70\text{S}$ ribosomes and DNA.
- Others: Lysosomes (catabolic enzymes), Peroxisomes (degrade toxins), Vacuoles (storage).
Endosymbiotic Theory: Suggests mitochondria and chloroplasts evolved from aerobic prokaryotes that entered larger anaerobic cells as parasites and became symbionts.

The microbe Mycoplasma is nonmotile; why is it alive?
Why did scientists initially think Epulopiscium was eukaryotic?
What discovery revealed that Epulopiscium is really a giant bacterium?
Why is a pilus a type of fimbria, but a flagellum is not?
Why is the microbe in Figure 3.2 more likely Gram-positive than Gram-negative?
Why does E. coli synthesize a potassium transport protein when grown in a hypertonic solution?
Why is B. anthracis able to survive in mail?
Why are bacterial and archaeal flagella considered analogous rather than evolutionary relations?
Why did 19th-century scientists think archaea were bacteria?
Why are archaea considered more closely related to eukaryotes than to bacteria?
Why are eukaryotic glycocalyces covalently bound to membranes, and why don't eukaryotes with cell walls have them?
Why aren't there many drugs that act against bacterial cytoplasmic membranes?
Why does colchicine (which inhibits microtubule formation) inhibit phagocytosis and organelle movement?