I. Prokaryotic Cell Structures. :
A. General Overview of Prokaryotes:
1. Prokaryotes compared to eukaryotes
a. no nuclear membrane
b. no membrane-bound organelles
c. DNA is circular
d. no histones associated with DNA
e. peptidoglycan usually in cell walls
f. divide by binary fission, not mitosis
g. smaller (70s) ribosomes
h. no cytoskeleton
i. smaller typical cell size
2. Bacterial morphologies
a. bacilli "little staff"
i. not the same as Bacillus, which is a genus name
b. cocci "berry shaped"
c. staphylo- "cluster"
d. strepto- "chain"
3. Glycocalyx - cell layer outside of plasma membrane
a. capsule - thicker gelatinous coat; for attachement and protection
b. slime layer - thinner, more fluid layer; more for gliding motility
4. Flagella - long protein filaments for motility
a. can be monotrichous, lophotrichous, peritrichous or ampitrichous arrangements
b. "corkscrew" action to propel bacterium forward
a. taxis refers to movement towards or away from external stimulus
b. flagella proteins can be very antigenic; useful in serotyping (e.g. E. coli O157:H7 serotype)
5. Axial filaments
a. flagella that wraps around cell body of spirochetes
b. turns entire cell in corkscrew manner for motility
6. Fimbriae and pili
a. fimbriae - tiny hairlike strands for attachment
b. pili - long tubelike projections for exchanging DNA between some bacteria (conjugation)
B. Peptidoglycan (murein):
1. layers of alternating sugars, sometimes multiple layers thick, with peptide linkages between
a. N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) sugar subunits
b. short peptide linkages between NAMs of adjacent polymers and layers holds cell wall rigid
2. Gram-positive cells have thick peptidoglycan + techoic acids for transport and stability
a. tend to be more sensitive to action of penicillin
b. penicillin interferes with peptide crosslinking, weakening newly produced cell walls
3. Gram-negative cell have thin peptidoglycan and outer membrane
a. less sensitive to penicillin
4. bacitracin interferes with NAM-NAG linkages - more broad spectrum antibiotic than penicillin
5. lysozyme (antibacterial enzyme in saliva) hydrolyses peptide linkages
6. Outer membrane of Gram-negative cells
a. outside of cell wall
b. contains lipopolysaccharide (LPS)
i. lipid-A portion (endotoxin) highly toxic, anaphylactic, inflammatory mediator
ii. O-polysaccharide not toxic, but antigenic, (e.g. E. coliO157:H7 serotype)
7. "unique" cell wall features
a. mycolic acid - waxy component of Mycobacterium species
b. no peptidoglycan - no cell wall in Mycoplasma species
C. Bacterial Endospores:
1. highly acid/heat/dehydration-resistant dormant stage
a. not a means of reproduction
b. few bacteria can produce endospores
i. Bacillus sporulates aerobically,
ii. Clostridium sporulates anaerobically, examples: C. perfringens, C. tetani, C. botulinum
c. can remain dormant for years (millions of years actually!)
d. ease of growth and storage makes Bacillus anthracis relatively easy and cheap biological weapon
D. Inclusion Bodies:
1. reserve deposits of various nutrients
a. metachromatic granules ("volutin" or phosphates), useful to ID Corynebacterium diphtheriae
b. others include: starch, sulfur, lipids, iron oxide (magnetosomes), and gas vacuoles.
This is only a general outline.
There may be material that has been discussed in lecture that is not included in this outline
and there may be material on this outline that has not been discussed in lecture.
Any material discussed in lecture or listed in this outline is "fair game" for the test.