morphology -
these prokaryotes are
typically ~0.2-2 x 1-5 um and may be cylindrical (bacilli), spherical (cocci),
helical (spirilla or spirochetes)
or polymorphic (many shaped or amorphous)
cell
wall - rigid structure (peptidoglycan +/- lipopolysaccharide) that protects
against osmotic pressure damage and provides cell shape - cylindrical (bacillus);
spherical (coccus); helical (spirillum)
cytoplasmic
membrane - this lipid/protein outer boundary of the cytoplasm regulates what
goes in and out of the cell (permeability)
ribosomes -
small RNA/protein particles required for protein synthesis
chromosome -
large single strand of DNA that contains the "blueprint" for all cell structure and activity
in regions called genes
plasmids -
DNA that contains only a few genes and is exchanged between bacteria (codes for antibiotic
resistance or virulence factors)
salts - no special requirements; pathogenic fungi grow well at salt
concentrations found in the human body
importance and habitat - mostly decomposers (saprophytes), but some are pathogens; prefer dark,
moist habitats containing organic material
Protozoa
morphology - these unicellular eukaryotes have
larger cells (10-100 um) than fungi or bacteria
cytoplasmic
membrane - this lipid/protein outer boundary of the cytoplasm regulates what
goes in and out of the cell (permeability)
cell wall - none, but many for a pellicle just "inside" the cytoplasmic
membrane
contractile
vacuoles - regulate osmotic pressure by water expulsion
ribosomes -
small RNA/protein particles required for protein synthesis
chromosomes -
multiple DNA-containing structures that contain the "blueprint" for all cell structure
and activity in regions called genes
pseudopodia or undilipodia (cilia, flagella)
provide motility
cyst - dormant form; protects against adverse conditions
growth - process of cell enlargement and proliferation (increase in number)
proliferate by:
binary fission - division of a cell into two cells of equal size
and composition
budding - division of a cell into two cells of unequal size, but
equivalent composition
zygote formation - during mating, gametes fuse to form a zygote, which develops
into a egg, then (when conditions are "right") matures to form offspring
nutritional requirements
chemical - they derive their energy and nutrition from organic compounds
that they digest intracellularly (holozoic) or from organic compounds that they
digest extracellularly using enzymes they secrete (saprozoic)
water - living biological entities are typically ~70% water
essential elements - C (carbon), H (hydrogen), O (oxygen), N (nitrogen),
P (phosphorus), S (sulfur)
trace elements - Ca (calcium), Mg (magnesium), Fe (iron), Na (sodium),
K (potassium), Zn (zinc), Co (cobalt), Mn (manganese), plus others
organic growth factors - vitamins and other essential organic nutrients
physical
temperature - pathogenic protozoa grow best between 20C and 40C
(human body temperature is 37C)
oxygen - most are aerobic, but some are anaerobic
pH - most infectious protozoa "prefer"
near-neutral conditions pH ~6-8
salts - no special requirements; pathogenic protozoa grow well at
salt concentrations found in the human body
importance and habitat - free-living protozoa (moist environments) are a basic part
of food chains and webs; parasites are major causes of infectious disease in
humans and other animals
Viruses
morphology -
very small (10 nm to 0.2 um)
nucleocapsid
nucleic acid - viral genes are made up of either DNA or RNA
capsid - protein coat made up of subunits called capsomeres
envelope - (optional) membrane "stolen" from host cell
growth -
they do not grow; they proliferate, but only inside host cells (viruses
are obligate intracellular parasites) by a process called replication,
which includes these steps:
attachment - to receptor sites on host cell by spikes
(peplomers)
penetration - entrance into host cell
uncoating - removal of capsid(s); frees the viral genes
to be expressed
synthesis - formation of viral DNA or RNA and proteins
assembly - components assemble to form viral nucleocapsids
release - viral particles (virions) "emerge" from the
host cell by lysis or "budding"
importance and habitat - pathogenic; ubiquitous, function
only in living cells