fungi stuff Flashcards
saprophytes
absorb nutrients from a dead organism
(most fungi)
necrophytes
derive nutrients from a organism they have killed
(parasite)
biotrophs
derive nutrients from living host
(parasite)
produce haustoria (growths in infected cells)
Cell wall made of?
chitin and polysacharrides
Where does mitosis take place in fungi?
In the nucleus
(other eukaryotes, mitosis occurs after nucleus broken down)
pseudohyphae
fungi can aggregate to form a colony or chain of cells
3 to 5 microns in diameter
What form do most fungi exist in?
filamentous form
Form of yeast
single cells with one nucleus, oval or spherical and reproduce asexually by budding off an identical daughter cell.
How do filamentous fungi grow?
grow by polarised tip growth where the growth is at the tip and not the base of the cell.
tip is where new cell wall and cytosol is synthesised
mycelium
collection of hyphae
dimorphic yeast
can grow as both yeasts and filamentous form.
environmental cues trigger transition(temp).
3 main type of spores and what they are.
condidospores - formed from specialised structure in a line of spores
sporangiospores - formed in specialised sac-like structures
arthrospores - formed from terminal cells of growing hyphae cells budding off.
when do fungi produce spore?
when they feel/sense stress
what are the two forms of sexual sporulation?
heterothallism - when two distinct parent cells which are sexually compatible join to form a unique offspring.
homothalism - when one fungus can self fertilise. no exchange of genetic material.
How are sexual spores generated?
Two haploid hyphae fuse and form a specialised cell in the dikaryon state ( the cell has two nuclei)
Then development of specialised cell which becomes diploid.
Then either:
generates diploid sexual spores and after germination it restores back to haploid state via meiosis.
or there is meiosis prior to sore formation and produces haploid sexual spores
dikaryon state
cell has two nuclei
fungal groups
zygomycetes
ascomycetes
basidiomycetes
chytridiomycetes (small group)
deutromycetes (an artificial grouping in that those fungi lack a sexual cycle)
Zygomycetes
produce sporangiospres in a sac structure, burst to release
aseptate hyphae
aseptate hyphae
no cross-cell wall and the long filamentous cell is a continuous large cell.
sexual reproduction in zygomycetes
plus and minus types are sexually compatible to fuse and form a zygosporangium and from this a diploid zygospore which undergoes meiosis to produce haploid spores which germinates to produce hyphae.
septate hyphae
filamentous cells are divided into smaller cells.
What kind of asexual spores do zygomycetes produce
haploid
example of glomeromycetes
mycohizzal fungi, symbiosis
What feeding mechanism are they?
saprophytes
Asexual reproduction in ascomycetes
ascomycetes form asexual condiospores from specialised aerial structures
sexual cycle of ascomycetes
cell fusion event and the formation of specialised dikaryon structures. From these structures, the cell fuses the nuclei to form the dikaryon state. The cell undergoes meiosis to produce four haploid sexual spores and each spore undergoes mitosis to form a total of eight spores. (ascospores)
ascomycetes
haploid septate hyphae
saprophytes
sexual reproduction in basidiomycetes
asexual reproduction rare
Spores are released from the fruiting body (e.g. toadstool) and two spores will germinate followed by fusion of the hyphal cell to make a single organism with two nuclei (dikaryon state). They propagate and grow as a dikaryon for most of the time as septate hyphae. It spends most of the time in the soil and when the conditions are favourable, they form a fruiting body (e.g. the mushroom) and from the gills spores are released
Specialised cell form of mushroom gills
basidium
basidiomycetes
septate dikaryon hyphae
asexual cycle uncommon
sexual haploid basidiospore in fruiting bodies
Most are saprophytes
fruiting bodies of basidiomycetes
basidiocarps - includes: toadstools, mushrooms and brackets and puffballs
How are fungi categorised/ grouped
based off sexual and asexual characteristics
deuteromycetes
absence of sexual reproduction cycle
The asexual spores can be produced in a variety of ways
mycoses
diseases caused by fungi
mycotoxins
produced by fungi can cause liver failure
true pathogen
affects healthy host
adapted to low oxygen tension and high temperatures
geographically restricted.
display thermal dimorphism (going from the fungal form to the pathogenic yeast form)
usually asymptomatic in host
obligate parasites
need to infect host to complete life cycle
thermal dimorphism
going from fungal form to pathogenic yeast form
hyphal form reproducing via spore production and being saprophytic at temperature less than 30 Celsius. If the spores become ingested, then the increase in temperature induces the yeast growth by budding or producing endospores (similar to that seen in bacteria) and they live a parasitic life deriving nutrients from the host. If it becomes systemic then this causes complications. On leaving the host environment, it reverts to its filamentous form
opportunistic fungal pathogens
host is usually compromised
hardy to host environment.
Commensalism
long-term biological interaction in which members of one species gain benefits while those of the other species are neither benefited nor harmed.
necrosis
death of body tissue
Dermatophytes
skin plants (translation)
They cause superficial infections on healthy host. They are not diseases and only cause discomfort.
key drugs to control fungal infections.
azoles (e.g. ketoconazole and fluconazole) and these prevent the demethylation of sterol to ergosterol (and essential component in fungal membrane lipid and is specific to fungi)
polyenes (e.g. amphotericin B); it is rather toxic to the host in that it causes liver and kidney failure but if you are being administered this drug then you are rather ill from a fungal infection!
It makes the membrane of the fungal cells leaky and the cytosol leaks out. It prefers fungi because it has a high binding affinity for ergosterol
5 fluorocytosine. It acts as a fungistatic (it slows and stops growth but does not kill the fungus and so when you come off the drug the fungus can regrow!). It works by replacing the cytosine in RNA synthesis and the RNA is non functional and it inhibits the fungus from making new proteins and thus stops or retards growth.
fungal cells more readily absorb the flourocytosine than animal cells making it partially fungal specific
phytopathogenic
cause diseases in plants
pathogens of mature tissue
either neurotrophic or biotrophic
show high degree of host specificity
rhizomorphs
macrostructures composed of filaments or hyphae cells.
haustauria
growth in infected cells
haustorium does not break and damage the plant cell plasma membrane (it only damages the cell wall), it grows inside the plant cell as a separate cell with its membrane up against the intact membrane of the plant cell. So the plant cell is functioning and the fungal cell takes nutrients from the cell from across the plant cell membrane. The haustorium becomes a nutrient sink.
typical infection cycle of fungi infecting insects
attachment of the spore to the cuticle,
this is followed by germination of an infection peg which penetrates the cuticle at the intersegmental portion gaining entry to the inside of the insect (it does this by employing cuticle digesting enzymes such as lipases, chitinases and proteases).
Following entry to the insect, it proliferates and sporulates in a yeast phase (they usually show dimorphism) and this results in one of two things; either the insect is drained of resource which eventually kills the insect or a toxin is used to kill the insect and the fungus derives nutrients from the dead insect. Following infection, the fungus can sporulate and produce spores for another cycle of infectio
intersegmental portion
weak point of cytoskeleton of insect.
control of fungi that parasite other plants, 3 things to consider
Parasitism of the target pathogen, using fungi to produce antibiotics targeted at the pathogenic fungus
and then competition in which a second fungus is introduced to out compete the target pathogenic fungus for nutrients.
mycoprotein
types of food that comes from a fungus
statins
fungal metabolites that inhibit the biosynthesis of cholesterol and are used to reduce plasma cholesterol levels which translates. into lower the incidence of heart disease.
statins inhibit a specific enzyme in the synthesis of chloresterol
