Lecture 20: Fungal Physiology and Life Cycles Flashcards
What are fungi?
animals and plants closely associated, branch off from fungi.
Eukaryotes
“any of a group of spore-producing organisms feeding on organic matter, including moulds, yeast, mushrooms, and toadstools.”
What are fungi?
animals and plants closely associated, branch off from fungi.
Eukaryotes
“any of a group of spore-producing organisms feeding on organic matter, including moulds, yeast, mushrooms, and toadstools.”
What are some unique characteristics of fungi?
- Unique lysine synthesis method
- AAA pathway
- AminoAdipic Acid pathway
- Animals = DAP pathway
- Ridged cell wall composed of beta-1,3
and beta-1,6 linked glucans, mannan
and chitin - Cell membranes contain “ergosterol”
(animals have cholesterol, plants have
sitosterol) - OFTEN A TARGET FOR
TREATING FUNGAL INFECTIONS
What are the 5 major fungal phyla?
- Basidiomycota
a. Most mushrooms, other
macroscopic fungi in this group - Ascomycota
a. Industrially important
b. e.g., penicillium (prod penicillin)
c. e.g., aspergillus (prod of chemicals)
d. Some macroscopic, most moulds - Glomeromycota
a. New phylum
b. Mycorrhizal fungi
c. Important symbiotic relationship
with plants - Zygomycota
a. Pin-head fungi - Chytridiomycota
a. water fungi
b. Mostly saprotrophs, some pathogen
c. Batrachochytrium dendrobatidis =
causes chytridiomycosis
What is the structure of fungal form?
1. Most fungi are filamentous, made of
"tubular", thread-like "hyphae"
2. Mass of hyphae is termed "mycelium"
3. Sometimes large macroscopic bodies
are produced
4. Some fungi unicellularWhat are hyphae?
- growth occurs at tips of hyphae
What is the structure of hyphae?
- Made of a thin transparent tubular cell
filled or lined with protoplasm.
a. Diameter: 1-30um - Hyphae are colourless (hyaline), fungal
colonies are coloured due to
pigmentation in spores - Tapered at the tip, called “extension
zone”
Where are hyphae located and where is the reproductive structure located?
When are reproductive structures produced?
Hyphae everywhere. Make up the fibrous “body”/structure
Reproductive structure: The head of the mushroom - spores located underneath the lip
Reproductive structures produces when moist and not too hot (autumn)
Where are hyphae located and where is the reproductive structure located?
When are reproductive structures produced?
Hyphae everywhere. Make up the fibrous “body”/structure
Reproductive structure: The head of the mushroom - spores located underneath the lip
Reproductive structures produces when moist and not too hot (autumn)
What is the role of fungal cell walls?
- Determine the shape of the fungus
- Act as an interface between the fungus
and its environment - Protect against osmotic lysis, regulates
passage of large molecules - Antigenic properties that can mediate
with the other organisms
What is the composition of fungal cell walls?
- 80-90% polysaccharides
- The chytridiomycota, ascomycota and
basidiomycota have “chitin”. - Zygomycota have mixture of “chitin” and
“chitosan”
Chitin - polymer of N-acetylglucosamine
a. also found in insect exoskeletons
Chitosan - polymer of D-glucosamine
a. deacetylated form of N-
acetylglucosamine
How is fungal cell walls strucutred/designed?
Four zones
- Amorphous glucans
- glycoprotein + protein
- Protein
- Chitin + protein
- Plasma membrane
What is the septa?
1. In most species; hyphae are
interrupted by cross-wall called
"septa"
2. Septa are usually perforated -
allowing passage of cytoplasm, and
even nuclei between parts of hyphae
3. May act as structural report
4. May be first line of defence against
damage
“SIMPLE” = septum has large central pole (Ascomycota)
“DOLIPORE” = septum (Basidiomycota), narrow central pole, flanked by bracket-shaped membranes called “PARENTHOSOMES” (clamp connections)
a. does not allow passage of nuclei,
ensures dikaryotic condition
What are Woronin bodies?
- Form just behind each septum
- Proteinaceous lattices surrounded by a
membrane - Plug the sepal pores if the hyphae are
damage, becoming old or undergoing
differentiation
What is differentiation in fungi?
- Dimorphism
- Development of structures involved in
sexual reproduction
What is meant by dimorphism in fungi?
- Can change between yeast and mycelial
form - Common for animal and human fungus
pathogens:
a. filamentous outside host
b. single cell inside the host - change from filamentous to yeast form
can be bought about by changing the
environmental conditions (e.g., oxygen,
sugar, calcium concentrations)
E.G., Candida albicans grows as a yeast in moist mucosal membranes of humans, but converts to hyphal to invade tissues
What is meant be apical growth
1. Fungal hyphae extend continuously at
extreme tips
2. Growth supported by continuous
movement of mineral into the tip from
the older regions of hyphae
3. Hyphae are a continuous movement of
protoplasm, which thrusts the growing
tip forwardWhat is the mechanism of apical growth?
- Growing tip of hyphae contains very few organelles, instead contains a body called “spitzenkorper” (apical body)
- This consists of a cluster of small, membrane bound vesicles embedded in a meshwork of actin microfilaments
- Its always present in growing tips, disappears when growth stops and reappears if growth restarts
How do fungi acquire nutrients?
1. Small organic food molecules
transported across plasma membrane
2. Polymeric food molecules must be
depolymerised
3. Depolymerizing enzymes are secreted
by vesicles fusing with the membraneHow and what two sexual processes do fungi perform?
- Sexual reproduction
- Asexual reproduction
Spores are essential for this.
How does asexual reproduction occur in fungi?
- Germination
- Mycelium (n)
- Spore producing structures (n)
- Spores (n)
- Repeat
How does sexual reproduction occur in fungi?
- Dikaryotic stage (n+n)
- Karyogamy (function of nuclei)
- Diploid stage (2n)
- Meiosis
- Spore producing structures (n)
- Spores (n)
- Germination
- Mycelium (n)
- Plasmogamy (fusion of cytoplasm)
- repeat
What are fungal mating types?
- Fungal mating types are determined by:
“mating-type locus” - Different mating types of fungi look the
same.
Why are spores “dispersed”?
1. To extend beyond the existing
environment
a. escape nutrient depletion
b. Exploit new potential environmental
nichesWhat are spores?
- Can be produced either sexually or asexually
2. Diverse; size, shape, structure, and colour
How are spores designed?
- Propelled far enough beyond the
surrounding fruiting body - Remain suspended in air currents to be
distributed appropriately - For small spores, take-off is limited by
drag, do high launch speeds is required
What disperses spores?
- Wind of air currents - most species
- Water - aquatic fungi
- Animals - vertebrates and invertebrates
- Host plants - particularly seeds
Before dispersal, all spores have to be released this is either active or passive
What is active liberation?
- Spores released from the hymenium
(spore producing surface)
What is passive spore liberation?
- External factors:
a. wind
b. rain
c. animals
What is the purpose of rain splash for fungi?
- Puff balls such as Lycoperdon (stump
puffball) - Spores produced in a sack like peridium
- When mature, peridium ruptures at
the apex and water droplets depress
the peridium, shooting a puff of
spores into the air
What is meant by insect dispersal?
- The stinkhorn, smells of rotting flesh, but
also contains lots of sugars which attracts
flies - Spores pass through gut of insect,
unharmed, dispersed via defecation - Some fungi are naturally florescent
- this luminescence attracts insects
