3.0 Fungi

Question 1

Fungal cell wall is mainly composed of _______________<br></br>Glucan = polymer of ___________<br></br>Mannan = polymer of __________

Answer 1

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>

Question 2

Plasma membranes of fungi contain ________

Answer 2

Plasma membranes of fungi contain <b>ergosterols</b>

Question 3

What is the structure of the fungal cell wall?

Answer 3

<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

Question 4

What is the structure of yeasts?

Answer 4

Unicellular<br></br>Round/oval <br></br>(candida can have pseudohyphae structure)

Question 5

What two types of mitosis occurs in yeasts?

Answer 5

1) Symmetrical binary fission<br></br>2) Asymmetrical budding

Question 6

What is the structure of filamentous moulds?

Answer 6

Multicellular<br></br>Hyphae (thin, branching cylinders)<br></br>Can be septate or aseptate<br></br>Mycelium = interwoven mass of hyphae

Question 7

How does mitosis occur in hyphae?

Answer 7

<b>Apical growth</b><br></br>-Mitosis only occurs at tips/side branches

Question 8

What are dimorphic fungi?

Answer 8

22 degrees = filamentous morphology<br></br><br></br>37 degrees = Yeast

Question 9

Brief overview of asexual reproduction:

Answer 9

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)

Question 10

What fungal species only reproduces using asexual reproduction?

Answer 10

Deutermycota

Question 11

Brief overview of sexual reproduction:

Answer 11

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

Question 12

What are the three different types of sexual spores?

Answer 12

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

Question 13

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

Answer 13

• 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

Question 14

Define saphrotrophs:

Answer 14

Fungi that feed on dead plant or animal material<br></br><br></br><b>Majority of fungi</b>

Question 15

What metabolites can fungi produce?

Answer 15

<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

Question 16

What are lectins?

Answer 16

Proteins that have a specific carbohydrate recognition domain (many fungal PRRs are lectins)

Question 17

List 6 fungal PAMPs and their PRRs:

Answer 17

<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

Question 18

What defects in host defences can lead to increased fungal infections?

Answer 18

<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

Question 19

What occurs following ingestion of the fungal toxin ergotamine?

Answer 19

It is a potent vasoconstrictor → ischamia and gangrene of digits

Question 20

What is a common commensal fungus?

Answer 20

Candida albicans (throat, gut and vagina)

Question 21

What is another name for superficial fungal infections?

Answer 21

Ringworm

Question 22

Examples of superficial fungal infections:

Answer 22

<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)

Question 23

Example of subcut fungal infection:

Answer 23

Rose picker’s disease (dimorphic sporothricx schenckii)

Question 24

Examples of systemic pathogens:

Answer 24

Histoplasma capsulatum

Question 25

Examples of systemic opportunists:

Answer 25

Candida<br></br>Pneumocystis jirovecii<br></br>Cryptococcus neoformans<br></br>Aspergillus fumigatus<br></br>Mucor