3.0 Fungi Flashcards
Fungal cell wall is mainly composed of _______________<br></br>Glucan = polymer of ___________<br></br>Mannan = polymer of __________
Fungal cell wall is mainly composed of <b>polysaccharides</b><br></br>Glucan = polymer of <b>glucose</b><br></br>Mannan = polymer of <b>mannose</b>
Plasma membranes of fungi contain ________
Plasma membranes of fungi contain <b>ergosterols</b>
What is the structure of the fungal cell wall?
<b>1) Inner chittin layer</b><br></br>Long straight chain<br></br>β-1,4-linked N-acetylglucosamine<br></br><br></br><b>2) Outer glucan layer</b><br></br>Branched chain<br></br>β-1,3-linked glucose<br></br><br></br><b>3) Embedded glycopeptides</b><br></br>Asparagine - N-linked mannose/galactose<br></br>Serine/threonine - O-linked mannose/galactose
What is the structure of yeasts?
Unicellular<br></br>Round/oval <br></br>(candida can have pseudohyphae structure)
What two types of mitosis occurs in yeasts?
1) Symmetrical binary fission<br></br>2) Asymmetrical budding
What is the structure of filamentous moulds?
Multicellular<br></br>Hyphae (thin, branching cylinders)<br></br>Can be septate or aseptate<br></br>Mycelium = interwoven mass of hyphae
How does mitosis occur in hyphae?
<b>Apical growth</b><br></br>-Mitosis only occurs at tips/side branches
What are dimorphic fungi?
22 degrees = filamentous morphology<br></br><br></br>37 degrees = Yeast
Brief overview of asexual reproduction:
Occurs most of the time<br></br><br></br>Spores produced by mitosis<br></br>Yeasts → internal spores<br></br>Moulds → external spores (condida) or internal spores (sporangium)
What fungal species only reproduces using asexual reproduction?
Deutermycota
Brief overview of sexual reproduction:
Haploid fungus → sexual structures (motile gametes or sexual hyphae)<br></br><br></br>2 x sexual structures fuse → nuclei fuse → diploid → re-assortment and recombination
What are the three different types of sexual spores?
1) Ones that form internally within tubules (<b>Ascus</b>)<br></br>2) Ones that form externally on club like structures (<b>Basidium</b><br></br>3) Ones that form from fusion of sexual hyphae
Complete the following statements regarding the nutrition of fungi:<br></br><br></br>• Fungi rely on preformed ______ compounds as sources of energy and carbon<br></br>• Secrete enzymes into the environment ⟶ ___________ <br></br>• Absorb simple soluble molecules through ___________<br></br>• Yeasts live in _______ environments<br></br>• Hyphae __________ food material
• Fungi rely on preformed <b>organic</b> compounds as sources of energy and carbon<br></br>• Secrete enzymes into the environment ⟶ <b>extracellular digestion of food material</b><br></br>• Absorb simple soluble molecules through <b>channels</b> in the fungal cell wall <br></br>• Yeasts live in <b>moist</b> environments<br></br>• Hyphae <b>penetrate</b> into food material
Define saphrotrophs:
Fungi that feed on dead plant or animal material<br></br><br></br><b>Majority of fungi</b>
What metabolites can fungi produce?
<b>1) CO₂</b><br></br><b>2) Ethanol</b><br></br><b>3) Antibiotics</b> - Pencillin, cephalosporin, streptomycin<br></br><b>4) Immuno-suppressants</b> - ciclosporin <br></br><b>5) Other drugs</b> - ergometrine, ergotamine<br></br><b>6) Toxins</b> - alphatoxins
What are lectins?
Proteins that have a specific carbohydrate recognition domain (many fungal PRRs are lectins)
List 6 fungal PAMPs and their PRRs:
<b>1) Mannose-rich structures</b><br></br>- Mannose binding lectin (MBL) ← soluble<br></br>- DC-sign<br></br>- Mincle<br></br><br></br><b>2) β-1,3-glucan</b><br></br>- Dectin-1<br></br><br></br><b>3) Mannans</b><br></br>- Dectin-2<br></br><br></br><b>4) Phosphidolipidomannans</b><br></br>- TLR2<br></br><br></br><b>5) O-linked mannose</b><br></br>- TLR4<br></br><br></br><b>6) N-linked mannose</b><br></br>- Mannose receptor
What defects in host defences can lead to increased fungal infections?
<b>1) Impaired fungal sensing (β-1,3-glucan)</b><br></br>- ↑ superficial infections<br></br>- Dextrin-1 deficiency<br></br>- CARD9 mutation<br></br><br></br><b>2) Impaired IL-17 immunity</b><br></br>- ↑ superficial infections<br></br>- IL-17 receptor deficiency<br></br>- Autoantibodies (anti IL-17/22)<br></br><br></br><b>3) Impaired neutrophils</b><br></br>- ↑ deep infections (Aspergillus)<br></br>- Post-chemo<br></br>- Inherited<br></br><br></br><b>4) Impaired T-cells/macrophages</b><br></br>- ↑ superficial + deep infections (Yeast + dimorphic)<br></br>- AIDs/transplant
What occurs following ingestion of the fungal toxin ergotamine?
It is a potent vasoconstrictor → ischamia and gangrene of digits
What is a common commensal fungus?
Candida albicans (throat, gut and vagina)
What is another name for superficial fungal infections?
Ringworm
Examples of superficial fungal infections:
<b>1) Dermatophye moulds</b><br></br>- Common<br></br>- Spores transmitted by person-to-person contact / sharing clothing<br></br>- Chronic infection → toxins → Type IV hypersensitivity<br></br><br></br><b>2) Candida Albicans</b><br></br>- Chronic finger nail infection<br></br><br></br><b>3) Malassezia furfur</b><br></br>- causes pityriasis versicolor (blotchy skin rash - does not tan)
Example of subcut fungal infection:
Rose picker’s disease (dimorphic sporothricx schenckii)
Examples of systemic pathogens:
Histoplasma capsulatum
Pneumocystis jirovecii
Cryptococcus neoformans
Aspergillus fumigatus
Mucor