Diagram and describe the general Ascomycotan life cycle. Know how it differs from, and is similar to, the Basidiomycotan life cycle.
(look @ phone)
- ascospores: haploid sexual spores produced by asci (sacs) in ascomycota
- ascospores germinate into monokaryotic hyphae
- (can undergo asexual reproduction where they form structures called conidia)
- if no asexual repro occurs, they will differentiate into precursors to asexual structures (antheridium or ascogonium)
- trichogyne grows out of the ascogonium
- plasogamy occurs: trichogyne forms a bridge so the nuclei and plasma can be transferred/joined between antheridium and ascogonium –> this means it’s now a DIKARYOTIC structure
- this structure produces ascogenous hyphae (out of the ascogonium) that contain nuclei
- the hyphae form a crozier’s hook that functions to separate out two nuclei so they can go through karyogamy
- the separate cell with the new diploid nucleus becomes the ascus mother cell
- nucleus undergoes meiosis to make 4 haploid nuclei
- nuclei undergo mitosis
- as meiosis and mitosis occurs, the cell elongates into an ascus, and then the nuclei develop into individual ascospores
- spores released from asci, cycle repeats
three major subphyla of the Ascomycota.
taphrinomycotina
saccharomycotina
pezizomycotina
Taphrinomycotina
- very diverse- no general characteristics, only discovered using molecular data/phylogenetic analysis
- deviate from typical ascomycotan life cycle- sometimes much more similar to basidiomycota
Major classes of the Taphrinomycotina.
- taphrinomycetes
- pneumocystidiomycetes
- neolectomycetes
- archaeorhizomycetes
- schizosaccharomycetes
taphrinomycetes
- dimorphic (yeast + hyphal stage) plant parasites
- causes leaf deformations (eg- leaf curl)
pneumocystidiomycetes
extracellular parasite of mammals- obligate (needs mammals for survival)- causes lung infections- particularly causes pneumonia in HIV/AIDS patients- reduced genome; must scavenge for amino acids in lungs
Describe the life cycle of Pneumocystis.
- sexual and asexual stages
- 1st step in sexual stage: haploid yeast cells undergo conjugation (2 yeast cells combining)
- now a dimorphic precyst structure
- meiosis occurs- duplication of organelles– now in early cyst stage
- matures into a full-cyst form containing lots of haploid cells inside
- excystment- cells are released from the cyst, cycle repeats
- asexual cycle: haploid cells duplicate by mitosis
neolectomycetes
- “irregular earth tongue”
- fruiting body is very similar to pezizomycotina
archaeorhizomycetes
- discovered bc of dna extraction from soil
- saprophytic potential
- abundant
- hyphal swellings- clamydospores- survival structures for rough envi conditions
schizosaccharomycetes
- fission yeasts
- live in high sugar envis
- used to make fermented beverages like millet beer
Describe the role of Saccharomyces cerevisiae in fermentation processes, including how the fermentation occurs.
- glycolysis turns glucose into 2 pyruvates
- pyruvates convert into acetaldehyde
- acetaldehyde converted into ethanol
- when ethanol is created, the electron carriers NAD+ are regenerated as a byproduct
- NAD+ used for glycolysis
Diagram the life cycle of Saccharomyces cerevisiae, describing each step.
- heterothallic: requires 2 diff mating types to undergo sexual repro
- haploid yeast cells undergo asexual budding
- 2 mating types meet and undergo plasogamy to form a dikaryotic schmoo
- schmoo undergoes karyogamy to form a diploid cell
- diploid cell can bud:
- either performs asexual budding to create more diploid cells, or…
- undergo meiosis to produce a young ascus w/ 4 haploid nuclei that can then develop into ascospores of either mating type
Explain the genetics of mating type switching seen in homothallic strains of this fungus.
HMLalpha MAT HMRa
| |
alpha copied |
restriction endonuclease
cuts out MAT
alpha replaces MAT
What are the 4 major antifungal groups?
azoles
polyenes
allyamines
echinocandins
Describe azoles, how they work
- work against ERGOSTEROL
- block the last step in the ergosterol pathway (pathway of ergosterol production)
- inhibitor of steroid biosynthesis
- eg: imidazoles, triazoles (more toxic)- both dangerous bc of similarity of clolesterol to ergosterol
Describe polyenes, how they work
- work against ERGOSTEROL
- long saturated hydrocarbon that binds to ergosterol
- eg: amphotercin B aka “amphoterrible”- can cause kidney damage
- all ergosterol targeting medicines somewhat dangerous bc of how close ergosterol is to cholesterol
Describe allyamines, how they work
- work against ERGOSTEROL
- stop a step in ergosterol pathway (inhibit squalene epoxidase)
- eg: Lamisil- used for skin infections
Describe echinocandins, how they work
- DO NOT target ergosterol
- inhibit production of beta 1-3 glucan synthase
- leads to eventual rupture of cell walls
- eg: caspofungin
various modes of resistance fungi evolve to combat antifungals.
- pumps that use proton gradient to pump compounds out of cells
- mutations altering sterol pathways, making drugs ineffective
- overexpression of compounds that antifungals inhibit
- biofilm formation: adhesion to a surface, protected by gelatinous outer layer
