4. Fungi Flashcards
What are some uses of fungi for humans?
- Sources of food or used for food fermentation
- Sources of pharmaceuticals
- Sources of enzymes
- Cause plant and animal diseases
What are the two ways in which fungi may grow?
Grow as filaments or as yeast
What is a mycelium?
The vegetative (feeding) structure is a mycelium - Mycelium is a network of hyphae
What are hyphae?
Monofilaments (cytoplasm in a tube) with large surface area: volume ratio
What are the cell walls of fungi like?
Cell walls feature chitin microfibrils embedded in a matrix of polysaccharides, protein and lipids
What is the mitosis yeast life cycle?
- Spindle pole replication
- Bud emergence
- DNA cell replication
- Nucleus migrates into the daughter cell
- Spindle formation
- Chromosome segregation; nuclear division
- Cytokinesis separated into mother cell and daughter cell
How are fungal hyphae divided?
Hyphae may be divided by cross walls called septa
What is the purpose of septa?
They are incomplete, allowing cytoplasmic continuity.
- Usually have pores that enable communication between cellular compartments
What happens when hyphae fuse?
Hyphae can fuse (anastomose), forming cells with mixed nuclei
What are cells with mixed nuclei known as?
Heterokaryons
What are all the different variations of fungal reproduction?
- Reproduce by producing hyphae
- Budding/fission (yeasts)
- Formation of sexual/asexual spores
What are dikaryons?
One haploid nucleus plus another haploid nucleus
How are dikaryons formed?
Plasmogamy (when plasma membranes fuse) of compatible mating types, then the fungus has nucleus from both parents
How do fungi receive their nutrition?
- They are heterotrophs
- Secrete enzymes and digest food externally
(Food absorbers)
What are food reserves in fungi stored as?
Reserves stored as glycogen, fats and oils
What do saprophytic fungi consume?
They decompose cellulose and lignin
Which environments do saprophytic fungi go in?
Environmental tolerance means they grow almost everywhere other organisms are found
What are mycorrhizae?
Fungal associates with plant roots in which fungus grows between and even into plant root cells
What do the fungi do in mycorrhizae?
Fungi extract sugars and fats from the plant in exchange for mineral nutrients and water it extracts from the soil
Why are fungi efficient soil nutrients extractors?
Due to large surface area to volume ratio of mycelia
What are endophytes?
Microbes that grow between leaf or root material, do not cause harm to the plant
What are lichens?
Fungi and algae beneficial associations
What have fungi evolved from?
Evolved from a protist similar to extant choanoflagellates - one line led to the sponges and animals, the other to the chytrids and other fungi
Ascomycota and … evolved from a shared ancestor?
Ascomycota and basidiomycota evolved from a shared ancestor “dikarya”
What environment are chytrids suited to?
Aquatic or soil borne
What is the motility of chytrids?
They are motile zoospores with a posterior flagellum
- The only fungi with flagella
What is the structure of the mycelium in chytrids?
Limited coenocytic mycelium ( no regular septa)
What are the relationships of chytrids with other organisms?
Parasites, saprophytes and mutualises
What is the structure of the mycelium of zygomycetes?
Hyphae are coenocytic (no regular septa)
What are zygospores?
Sexual spores of zygomycetes
What are sporangiospores?
Asexual spores of zygomycetes
What are some examples of zygomycetes?
Fruit moulds, insect pathogens
- Uncommon human pathogens
What are ascomycotes? Examples
Yeast, truffles, cup fungi, moulds
What is the structure of the mycelium of ascomycetes?
Hyphae have regular septa
Where is dikaryon seen in ascomycetes?
Dikaryon limiters to reproductive tissue
What is the role of meiosis in the ascomycete reproductive cycle?
Meiosis follows zygote formation within the ascus, forming ascospores
- Asci may be surrounded by a fruiting body (ascocarp)
What are the asexual spores of ascomycetes known as?
Condia
What are some examples of basidiomycota?
Mushrooms, toadstools, rusts, puffballs
What is the mycelium structure of basidiomycota?
Vegetative hyphae are septate
Are conidia present in basidiomycota?
Asexual conidia are uncommon
What is the reproductive cycle of basidiomycota?
- The basidium is the characteristic sexual reproductive structure of the basidiomycetes. Basidiospores form outside the basidium
- Basidiospores give rise to haploid hyphae
- Haploid hyphae of different mating types fuse, forming dikaryotic hyphae
- The dikaryotic mycelium grows and eventually produces a fruiting structure, the basidiocarp
- The basidiocarp is topped by a cap, or pileus, which has gills on its underside
- Basidia develop on the surface of the gills
- Nuclear fusion and meiosis take place in the developing basidium
What does the MAT locus control?
A mating type locus has been found in all fungi to date to control their ability to undergo sexual reproduction.
What genes are encoded on the MAT locus?
Genes encode global regulators such as high mobility group (HMG) transcription factors (which are similar to human SRY gene on Y chromosome which controls male development)
