Chapter 18: Prokaryotes & Viruses
Formerly, the Kingdom Monera (except viruses)
Kingdom ArchaebacteriaCanaerobic and aerobic
bacteria adapted to extreme environments; prokaryotic;
differ from eubacteria in structure of cell membrane
and cell wall; RNA polymerase and ribosomal protein
suggests a closer similarity to eukaryotes than to
eubacteria; fewer than 100 named species, divided into
3 broad groups:
MethanogensCanaerobic methane producers; most
species use CO2 as a carbon source; found in soil,
swamps, and the digestive tracts of grazing mammals
such as cattle; produce nearly 2 trillion kg of methan (2
billion tons) of methane gas annually
ThermoacidophilesCInhabit very hot
environments that are often very acidic; some species
can tolerate temperatures of 100 degrees C (230 d. F);
require sulfur; nearly all are anaerobes
Extreme HalophilesCLive in environments with a
very high salt content, including the Dead Sea and the
Great Salt Lake; nearly all are aerobic; all are gram
negative
Kingdom EubacteriaCtypically unicellular;
prokaryotic; without membrane-bound organelles;
nutrition mainly by absorption; reproduction by fission
or budding; about 5,000 species (undoubtedly more)
Chemoautotrophs, enterobacteria, pseudomonads,
spriochaetes, actinomycetes, rickettsias
I. Origins of Prokaryotes
A. Fossil record
1. 32 billion yrs. old
a. oldest eukaryote is only 2-22 billion yrs
old.
2. are cyanobacteria (blue-green algae)
a. photosynthetic
B. Origins???
1. Extraterrestrial origins (meteor/asteroid)
2. Divine creationCuntestable
3. Spontaneous orgins
a. A.I. OparinCrussian scientist
1) attempted to describe early
atmosphere
2) believed it contained no oxygen, but
methane, ammonia, nitrogen and
hydrogen gases
3) believed that small organic molecules
spontaneously formed from inorganic
gases
b. The Urey-Miller hypothesis
1) tested Oparin=s theory
2) successfully produced amino acids,
fatty acids, and small hydrocarbons in
a chamber in the absence of oxygen
a) knew this could never have
worked in the presence of oxygen
b)
UV light would have
destroyed methane and
ammonia; also time problem
c. current theory
1) RNA was the first self-replicating
(complex) organic molecule; proteins,
DNA, etc. DO NOT spontaneously
form in water
2) presently, scientists think that life
began on solid ground
d. Lerman=s Bubble Model
1) waves and volcanic action caused
bubbles in ancient oceans
2) gases, protected by bubbles, could
have reacted to produce small organic
molecules (could also have been
tossed up onto solid ground)
II. Biology of Prokaryotes
A. Cell structure
1. 1-10 m (1/10 the size of eukaryotes)
2. have no membrane-bound organelles
B. ecological niches
1. heterotrophs: require complex organic food
sources, generally produced by other
organisms
a. are the Agerms@
b. frequently pathogenic (diseasecausing)
2. autotrophs: Aself@-feeding (phototrophs)
chemotrophs, etc.
C. Cell structure
1. cell membrane (plasma membrane)
2. cell wall
a. techoic acid (archaebacteria) or
peptidoglycan (most eubacteria)
b. many antibiotics inhibit peptidoglycan
synthesis
3. capsuleCslimy outer layer
4. nucleoid region (no organized nucleus)
a. location of the single, circular
chromosome
1) plasmids, additional separate pieces
of DNA, exists in some bacteria
5. mesosome: inward extension of plasma
membrane believed to aid in separation of
DNA replicas
6. pili: used to attach to surfaces, provokes
antigenic reactions in hosts, helps to avoid
being phagocytized by macrophages
7. flagellum: s-shaped structure used as a propeller to aid in locomotion
D. Significance of the cell wall
1. thick cell walls are affected by antibiotics
(inhibition)
2. readily retain crystal violet stain (Gram
positive)
a. Gram negative bacteria have thinner cell
walls, and do no retain crystal violet; are
not susceptible to penicillin
1) requires tetracycline, streptomycin,
etc to inhibit protein synthesis
3. endospores
a. thick-walled, resistant bacterial forms
1) are dehydrated
2) can be germinated
III. Cell form and arrangement (morphology)
A. bacillus (-i): rod-like cells, in chains or singles
B. cocci: single spheres
C. diplococci: double spheres
D. sarcina: group of 8
E. spirochaete: helix
1. different form of spirillum
a) spirochaete has axial filaments
b) spirillum has flagellum
F. Vibrio: comma shaped
IV. Reproduction
A. Simple binary fission w/o mitosis or meiosis
1. very common
2. ex. E coli can divide every 20 minutes (4.7
x 1021 [4.7 sextillion]) bacteria will exist within
one day
V. Heterotrophy
A. Decomposers gain energy through decay
1. saprobes—secrete enzymes to break down
organic matter
2. are economically significant
a. release ions for re-use (NO3, PO43-, etc.
are part of the nitrogen cycle)
B. Inhibition of saprophytic activity
1. must make conditions unfavorable, like
cooking, drying, freezing, salting, heating
2. pasteurization, preservatives used to deter
activity (sorbic acid, calcium proprionate)
C. Some decomposers are useful
1. foods: flavoring
2. hormones, antibiotics, vitamins
a. ex: E coli in human bowel releases
vitamins (“normal flora”)