Eukaryotic Cell Structure and Function

mycology

study of fungi

fungi

prominent “decomposers” of dead and decaying matter

secrete exoenzymes and absorb nutrients

saprophyte

describes fungi’s role in nature-live on dead material

example of single celled fungi

yeasts

used in baking and brewing

some cause disease

example of multicellular fungi

molds and mushrooms

filamentous decomposers

some cause animal and plant disease

yeasts

oval shaped

reproduce asexually by budding

appear pasty and form large colonies when grown on special agar medium buffered to an acidic pH

molds

filamentous (fuzzy) fungi

cells are tub like and connected into long filaments called hyphae or mycelium

can branch off, form rhizoid root-like cells, aerial mycelium with spore containing structures

some filaments have cross walls separating individual cells and others appear as a multinucleate mass

some are “dimorphic”

dimorphic

two forms: grow in nature as molds but in our bodies grow as yeasts

characteristics of fungi

saprophytes

heterotrophic

cell walls of chitin

few are parasitic

few cause serious human disease

distribution of fungi

ubiquitous

prefer slightly cooler and more acidic environments than bacteria

ubiquitous

anywhere, any environment, temp. food source, etc.

economic importance of fungi

greatest negative impact is plant disease and crop loss

Irish potato famine

rusts, smuts, powdery mildew

medical importance of fungi

many human pathogens

we are pretty resistant to fungal infections

some opportunists: candida and dermatophytes (ringworms)

ascomycetes

sexual spores in an ascus (sac)

protozoans

kindgom: protista

formerly thought of as “animals”

generally have no cell walls

most exhibit two distinct life forms: trophozoite and a cyst

distribution of protozoans

most are free living in watery environments

have developed special structure to expel excess water taken on in a fresh water environment

have a variety of mechanisms for obtaining food

trophozoite

(troph)

an active feeding form

cyst

non-active

“survival form”

medical importance of protozoans

many are parasites spread by the fecal-oral route

most acquire infections by ingesting the encysted form in contaminated food or water

how are protozoans classified?

based on “motility”

flagellates (mastigophora)

motile by flagella

i.e. free living euglena and parasites giardia and typanosoma

trypanosoma

sleeping sickness, transmitted via TSETSE fly

sarcodinans

amoebas motile by pseudopods

many are free living

some are parasites and cause disease (usually fecal-oral)

ciliates

motile by “cilia”

free living paramecium and intestinal pathogen-balanditium coli

sporozoans (apocomplexa)

not motile

very complex life cycles often with a vector

plasmodium species causing malaria with a mosquito vector

toxoplasma parasite from cat litter box

multicellular parasites

helminths, the worms

these diseases are often diagnosed with microscopic examination of stool samples for characteristic eggs

classified based on body form of adult worm (round or flat)

plathelminths

flat worms

two divisions

nematodes

round worms

very diverse group

from tiny, thread-like, to giant pork roundworm (ascaris)

cestodes

tape worms

often long and segmented

scolex

segments: proglottids, as they mature produce fertile eggs

trematodes

“flukes” leaf like body forms

non-segmented

complex life cycles

many intermediate hosts (snails, fish)

even free swimming larvae in contaminated water

scolex

holdfast structure attached to intestine

how cestodes are distributed

either segments or eggs pass in the stool and contaminate water or food

prevention of cestodes

meat inspection, treated water, cooked food, and good hygiene

examples of nematodes

pinworms (a family affair)

enterobrius vermicularis (itchy butt, followed by scotch tape test)

hookworm

necator americanus

larva in warm moist soil, wear shoes

ascaris lumbricoides

giant pork roundworm (adults 12 inches long)

can block intestine

common in pets

trichinella spiralis

cook pork, bear, and horse meat

anthropod vectors

animals with “jointed” feet, bite and transmit micorbes

what disease can fleas cause?

plague, rabbit fever

what disease can mosquitoes cause?

malaria

what disease can body louse cause?

typhus

what disease can flies cause?

sleeping sickness

what disease can kissing bug (Reduvids) cause?

American sleeping sickness

what disease can ticks cause?

arachnids, lyme disease, spotted fevers