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MolMic > Fungi > Flashcards

Fungi Flashcards

1
Q

What are the functions of fungal spores?

A

Reproduction - asexual/sexual
Dispersal - structural adaptations
Survival - low water content, thick cell walls, pigmentation

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2
Q

What is a ‘mycelium’?

A

Complex, interconnected network of hyphae, grown from spores, 3D

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3
Q

What are germ tubes?

A

Specialised hyphae, emerge during spore germination, involved in colony establishment
Hyphal growth polarised

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4
Q

How do microtubules act in germinating spores?

A

Lengthen (polymerisation) and shorten (depolymerisation), regulated by different enzymes
Dynamic instability

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5
Q

How do motor proteins act on microtubules?

A

Transport ‘cargo’ along microtubules and actin microfilaments
Cargo = membranous organelles, vesicles, RNA, and protein complexes

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6
Q

What are the 3 types of motor proteins?

A 
Microtubule-associated:
Kinesins - 'walk' to + end
Dyenins - 'walk' to - end
Actin-associated:
Myosins

Consist of homodimer of heavy chains and some number of light chains
Heavy chain bind to microtubule
ATP hydrolysis lead to conformational changes

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7
Q

What is the dominant fungal lifestyle?

A

Filamentous fungal lifestyle

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8
Q

How does possession of hyphae demonstrate uniqueness of filamentous fungi?

A

Non-motile heterotrophic organisms
Ability to adapt to environment
Ability to undergo morphogenesis

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9
Q

What are the functions of hyphae?

A 
Exploration and resource capture
Nutrient mobilisation
Translocation of nutrients and water
Defence of occupied substratum
Reproduction
Survival
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10
Q

Why are some septal pores unplugged in peripheral growth zone of hypha?

A

Allows mass transport of protoplasm towards hyphal tip

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11
Q

What is a Spitzenkorper?

A

Concentration of vesicles as well as actin, microtubules, and other proteins
Viewed as:
Vesicle supply centre
Vesicle receiving centre
Primary response element to internal and external signals

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12
Q

What are chitosomes?

A

Located in spitzenkorper core
7 different chitin synthases
Microvesicles which can each synthesise a single chitin microfibril

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13
Q

How are sites of chitin synthesis located?

A

Miroautoradiography

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14
Q

What are hyphal walls made of?

A

2-component system - microfibrils composed of chitin, amorphous matrix composed of glucans and proteins

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15
Q

Why are microtubules important?

A

Secretory vesicle transport and tip growth

Kinesin motor proteins required to maintain polarised growth

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16
Q

What shows actin is involved in hyphal tip growth?

A

Actin microfilaments concentrated in Spitzenkorper core
Actin nucleating protein, formin, concentrated in Spitezenkorper
Myosin enriched in hyphal tips

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17
Q

What is the proposed secretory pathway in growing hyphae?

A

Short distance transport of secretory vesicles and exocytosis of apical plasma membrane via actin microfilaments and myosin
Spitzenkorper = vesicle receiving and supply centre and switching station for vesicles to ‘hop-off’ microtubules and ‘hop-on’ actin microfilaments to their final destination
Long-distance transport via microtubules and dyenin/kinesin

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18
Q

What’s the classical view of secretory pathway in fungal hypahe?

A

ER -> Golgi -> Spitzenkorper
Proteins synthesised on ER, transported to Golgi
Proteins glycosylated and packed in secretory vesicles
Secretory vesicles transported to Spitzenkorper
Secretory vesicles targeted to apical plasma membrane and exocytosed

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19
Q

What are important functions of endocytosis?

A

Recycling membrane proteins and lipids
Internalisation of proteins and lipids for degradation
Internalisation of signal molecules

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20
Q

Where is endocytosis concentrated?

A

In a subapical ring just behind growing tip

21
Q

Where does hyphal fusion occur?

A

In colony interior

Occurs in mature/older parts of fungal colony

22
Q

How can fungal fusion be observed?

A

Fluorescent staining of mycelium

23
Q

How does hyphal fusion occur?

A

Pre-contact stage - spitzenkorper forms on both hyphae
Spitzenkorper grow towards each other
Post-contact stage - adhesive glue produced and hyphae connect
Fusion of hyphae and cytoplasmic mixing

24
Q

What are ‘nuclear comets’?

A

Dynamic aggregations of nuclei and organelles in mycelium of Neurospora
Unimpeded by septa
Only observed in central regions

25
Q

In which direction do nuclei usually travel?

A

Towards growing edge of colony

Sometimes towards sites of conidia production

26
Q

What decides velocity of nuclei?

A

Diameter of hyphae

27
Q

Do all nuclei move with flow of nuclear comets?

A

No some show resistance

Some may be tethered by spindle pole bodies

28
Q

What is a ‘rhizomorphic’ mycelium?

A

Aggregated hyphae in mycelium
Thick strands of hyphae which have adhered
Helps fungus cover area, grow quickly through, substrates and establish a feeding network
Coated in melanin in thick protective layer
Eg. honey fungus

29
Q

What are the different guises of cell polarity regulation in fungi?

A

Initiation of cell polarity - spore germination, branch-formation, yeast-hypha dimorphism
Maintenance of cell polarity - hyphal growth
Re-orientation of cell polarity - hyphal growth, externally imposed polarity
Loss of polarity - sporulation, infection structure formation

30
Q

What are the mechanisms of spore liberation?

A 
Water drop splash
Fall of basidiospores
Wind
Puff ball 
Ascus guns
Pick up by mist
31
Q

What is the importance of fungi?

A

Parasites - plant and animal
Mutualists - mycorrhizae and lichen
Saprotrophs - carbon cycle, sewage disposal
Fungal products - food, ripening of cheese, alcohol, bread etc.

32
Q

What are lichens?

A 
Dual organisms - fungi and algae
Slow growth rates, long-lived
Occupy nutrient-poor environments
Resistant to desiccation and environmental extremes
Sensitive to pollution
Also contain yeast!
33
Q

What types of mycorrhizal relationships are there?

A

Ectotrophic - eg basidiomycota and tree host
Arbuscular - eg. glomus, obligate biotrophs
Endotrphic - eg. rhizoctonia, and orchid host

34
Q

How do basidiomycota spread spores?

A

Gills, pores, spines

Basidiospores released from basidia

35
Q

What are the different types of fungal nutrition?

A

Saprotrophy - non-living organic material used as nutrient resource
Necrotrophy - living tissue first killed then used as nutrient resource
Biotrophy - living tissue used as nutrient resource

36
Q

Where can fungi invade plant tissues?

A 
Fruit and seed infection
Epiphytic growth
Invasion of photosynthetic tissues
Local lesions
Vascular wilt
General systemic spread
Canker
Heartrot
Root rot
37
Q

How does ‘the powdery mildew’/E. graminis (ascomycota) infect plants?

A

Has haustorium in plant epidermal cell
Invading hypha penetrates host cell wall and forms haustorium
Separated from host cell by extrahaustorial membrane
across which fungus draws nutrients

38
Q

How do ‘wheat stem rust’ hyphae grow?

A

Growth at right angles to ridges indicating surface topography induces directional growth
Aim to get to stomata - increases probability
Growth into grooves
Appressorium penetrates stoma of plant leaf

39
Q

How do ‘bean rust’ hyphae grow?

A

Appressorium induced bu 0.5 um ridge of guard cell

Appressorium gorw to produce haustorium in plant epidermal cell

40
Q

How do appressorium work?

A

Builds up pressure by osmotic uptake of water through melanin layer
Glycerol acts as solute which aids water retention
Pressure pushes through cell wall

41
Q

How do some spores stay on plants?

A

‘Spore top mucilage’ glues spores to plant leaves

42
Q

How do plants prevent infection?

A

Necrosis of plant cells - hypersensitive response to prevent further infection

43
Q

What is fluorescence?

A

Excitation of a substance and emission of light

44
Q

What’s an example of a fluorescent protein?

A

GFP - produced by jellyfish

45
Q

Why is GFP useful?

A

Good for studying cell biology of living cells
More FPs available now
Protein/organelle labelling
Non-invasive investigation of living cells

46
Q

What is bioluminescence?

A

Production and emission of light from a living organism

47
Q

What is an eg of a bioluminescent bacteria?

A

Photobacterium phosphoreum
Marine bacteria associated with light organs on angler fish
Regulated by quorum sensing
Light increases at higher cell densities

48
Q

How does firefly bioluminescence work?

A

Luciferase catalyses oxidation of luciferin resulting in light emission
ATP dependent in fireflies
Many diff types luciferins and luciferases in diff organisms

49
Q

What is aequorin?

A

A luciferase that binds to a luciferin to form a single photoprotein
Binding of calcium ions results in change in photoprotein structure and oxidation of the luciferin substrate results in emission of blue light
Presence of GFP results in conversion to green light

MolMic (5 decks)

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