Microbiology Notes 9/4/09

Major Categories of Microbes
I. Definition of Microbes: any organism so small it can’t be seen with naked eye
II. Eukaryotes: cells have nuclei
a. Nucleus: membrane bag surrounding DNA.
b. Most kinds of eukaryotes on earth are microscopic. Most are single-celled.
c. Figure 1.27b
d. ALL Eukaryotes very genetically similar to each other.
III. Prokaryotes: Cells without a nuclei.
a. Archaea: Thought to have not changed much for billions of years. No nucleus, like bacteria, but otherwise more similar to eukaryotic cells than to bacteria.
i. Cell membrane chemistry like chemistry like Eukarya, RNA polymerase like that of eukaryotes
1. Enzyme that does treanscription
ii. Extremophiles
1. Live in extreme environments
a. Geysers
b. Ocean vents
c. Other water with very high (>100o) temps
d. Dead Sea
e. Lots of others……
b. Bacteria- Distinct cell wall, cell membrane structures not found in Archaea or Eukaryotes. Distinct RNA polymerase.
i. Gram-positive- Minority of bacteria on earth, but important clinically.
1. Plasma membrane
a. Phospholipid bilayer.
2. Peptidoglycan cell wall with Lipoteichoic acid (LTA)
a. Glycan=Carbohydrate sugar component
b. Peptid=Protein component
c. ~30 + layers
d. Cross linked with Lipoteichoic acid
i. Fatty acid
ii. Unique to gram-positive bacteria
ii. Gram-negative
1. Plasma membrane
2. Peptidoglycan cell wall with no LTA
a. Just ~ 5 layers of peptidoglycan in cell wall
3. Periplasmic space
a. Between the inner cell wall and outer membrane
4. Outer membrane containing Lipopolysaccharide (LPS)
a. Like the phospholipid bilayer
b. contains LPS
i. unique to gram-negative bacteria
ii. Figure 1, p324- Saier
1. Inside leaflet made of phospholipids
2. Outside leaflet made of lipopolysaccharide
iii. Other Poinst on LPS and LTA
1. Inflammatory response reacts very violently against non-Eukaryotic chemicals.
2. So, too much LPS or LTA in blood  violent inflammation, often death
a. Lipid A, inside part of LPS,  most violent response.
3. Sepsis is not really dying of bacteria in the blood, people with sepsis really die of the violent inflammatory response
iv. Acid-fast
1. Plasma membrane
2. Cell wall containing LTA
3. Outer membrane (more like an additional wall) containing mycolic acid
a. Dense waxy molecules
b. Hydrophobic
c. Resistant to drying out (desiccation)  can survive for a long time in dry environments
i. Lots of soil bacteria are acid-fast
ii. TB and leprosy included here
d. Waxy mycolic acid prevents gram stains from penetrating bacterial cell envelope.
4. Figure 2 p 325- Saier
Consequences of cell wall made of peptidoglycan
Clearly defined shapes
Round/spherical: Cocci
Tubes/cylindrical: Bacilli
Spirochetes: spiral/ corkscrew

v. Mycoplasmas- lack a cell wall completely, so no clearly defined shape
1. Plasma Membrane
2. Maybe another membrane (not necessarily the same as gram-negatives’ outer membrane. Though.)
a. Chlamydia

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