Fungi Flashcards
What are four key features that distinguish fungi as a unique kingdom?
Chitin cell walls.
Ergosterol in fungal membranes.
80S ribosomes.
Reproduction via spores.
What is the ecological role of mycorrhizal fungi?
They form symbiotic relationships with plant roots, exchanging minerals like phosphate and nitrogen for plant-derived sugars.
This enhances plant health and ecosystem productivity.
How do teleomorph and anamorph stages differ in fungal life cycles?
Teleomorph: Sexual reproductive stage, involving meiosis and often forming fruiting bodies.
Anamorph: Asexual stage, typically more common and producing mitotic spores.
Give examples of fungi with economic importance and their applications.
Saccharomyces cerevisiae is used in baking and brewing. Penicillium species produce antibiotics like penicillin.
How do fungi contribute to soil formation and nutrient cycling?
Fungi break down rocks and organic matter with enzymes, aiding soil formation and releasing nutrients like nitrogen and phosphorus, critical for plant and ecosystem health.
Why are fungal infections difficult to treat in humans?
- Fungi are eukaryotes like humans, limiting drug targets.
- Treatments risk harming host cells, diagnostics are poor, and resistance is increasing.
- Some fungi are also part of the normal microbiota.
Compare moulds and yeasts with examples.
- Moulds (e.g., Aspergillus fumigatus) are multicellular and filamentous.
- Yeasts (e.g., Candida albicans) are unicellular, forming smooth colonies.
What is Calcofluor White and how is it used?
It is a fluorescent dye that binds to chitin in fungal cell walls, used in microscopy to help identify fungal cells by their blue-white glow under UV light.
What are aflatoxins and why are they dangerous?
Aflatoxins are toxic, carcinogenic compounds produced by Aspergillus species.
They contaminate food and can cause severe liver damage, especially in immunocompromised individuals.
How do fungi reproduce, and why are spores important?
Fungi reproduce sexually and asexually through spores, which enable survival, dispersal, and colonisation. This versatility supports adaptation to varied environments.
Name the six fungal phyla.
- Ascomycota
- Basidiomycota
- Chytridiomycota
- Cryptomycota
- Glomeromycota
- Zygomycota
What is the role of hyphae and mycelium in fungal structure?
Hyphae are thread-like filaments; a network of hyphae forms a mycelium, the main body of multicellular fungi, which absorbs nutrients.
Describe the fungal life cycle of club fungi (Basidiomycota).
Begins with haploid mycelium (n), followed by plasmogamy forming dikaryotic mycelium (n+n). This develops into a basidiocarp (mushroom), where karyogamy and meiosis occur in basidia, producing haploid spores.
Why are fungi classified as chemoorganotrophs and osmotrophs?
They oxidise organic compounds for energy (chemoorganotrophy) and absorb dissolved nutrients across membranes (osmotrophy), rather than photosynthesising.
Why are fungal infections becoming a greater concern globally?
Rising global temperatures, more immunocompromised patients, and increasing antifungal resistance are all contributing to higher infection rates and mortality.
What is the difference between a primary fungal pathogen and an opportunistic fungal pathogen? Provide an example of each.
Primary pathogens cause disease in healthy individuals (e.g., Blastomyces dermatitidis). Opportunistic pathogens primarily affect immunocompromised individuals (e.g., Candida albicans).
Define “pathogenicity” and “virulence.” How do they differ?
Pathogenicity is the ability of a microbe to cause disease. Virulence refers to the degree of pathogenicity, or how severe the disease caused by the microbe is.
Name three virulence factors employed by fungi and explain their role in pathogenesis.
Biofilm formation: Protects fungi from immune responses and antifungal treatments. Hydrolytic enzymes: Break down host tissues to obtain nutrients and aid tissue invasion. Morphogenesis: Switching between yeast and hyphal forms (e.g., Candida albicans) helps with dissemination and tissue penetration.
What are the main risk factors for invasive aspergillosis, and why is Aspergillus fumigatus such a successful pathogen?
Risk factors include chemotherapy, exposure to compost, and contaminated air conditioning. A. fumigatus thrives due to its environmental ubiquity, thermotolerance, and the ease with which its spores are inhaled.
Describe the geographical distribution and symptoms of coccidioidomycosis (Valley Fever).
Coccidioides immitis is endemic to the southwestern US and Mexico. Symptoms include fever, cough, headache, and muscle pain, often with a flu-like presentation.
Where is Cryptococcus neoformans typically found, and how is it diagnosed?
Found in trees and pigeon droppings. Diagnosis includes India ink staining of cerebrospinal fluid (CSF) and Cryptococcal Antigen (CrAg) testing in CSF, serum, or plasma.
How does Candida albicans behave as both a commensal organism and a pathogen?
C. albicans is part of the normal microbiota, especially in the mouth and GI tract. It becomes pathogenic under conditions like immune suppression, causing superficial and systemic infections.
What is candidalysin, and what role does it play in Candida albicans infections?
Candidalysin is a peptide toxin produced by C. albicans that disrupts host cells, activates inflammatory pathways, and aids in tissue invasion.
List the four major classes of antifungal drugs and explain their mechanisms of action.
Azoles: Inhibit ergosterol synthesis, disrupting cell membrane integrity. Polyenes: Bind ergosterol, creating pores in the cell membrane. 5-Flucytosine: Inhibits nucleic acid synthesis. Echinocandins: Inhibit beta-(1,3)-d-glucan synthase, blocking cell wall synthesis.
