FUNGI CHAPTER 24

describe the nucleus structure of a fungal cell

• As eukaryotes, fungal cells contain a membrane-bound nucleus

• The DNA in the nucleus is wrapped around histone proteins

• A few types of fungi have accessory genomic structures comparable to bacterial plasmids (loops of DNA)

True or False: Horizontal transfer of genetic information that occurs between one bacterium and another also often occurs in fungi

FALSE

Hh\ow does the structure of fungal cells differ from plant cells?

Unlike plant cells, fungal cells do not have chloroplasts or chlorophyll

What organelles do fungal cells contain?

Fungal cells also contain mitochondria and a complex system of internal membranes, including the endoplasmic reticulum and Golgi apparatus

What function to the pigments in fungi have?

• Pigments in fungi are associated with the cell wall and play a protective role against ultraviolet radiation

• Some fungal pigments are toxic to humans

Describe the structure of fungal cell walls

• The rigid layers of fungal cell walls contain complex polysaccharides called chitin and glucans

• Chitin (N-acetyl-D-glucosamine), gives structural strength to the cell walls of fungi

What is ergosterol?

Fungal plasma membranes are stabilized by ergosterol: a steroid molecule that replaces the cholesterol found in animal cell membranes

Give examples of fungi

• bread mold

• mushrooms

• shelf fungus

• puffballs

• cup fungi

What environment do Chytrids live in?

Aquatic

Where do unicellular yeast fungi live? Give 2 examples of unicellular yeast fungi.

• Live on water films and moist tissue

• EX: Brewer’s yeast and vaginal yeast

What is mycelium?

• The main fungus body is a mycelium

• a network of filamentous (thread-like) hyphae (singular-hypha) often unseen: underground or within hosts

• feeds & grows; often enormous

What are Hyphae? What is it made of? What does the cell membrane contain?

• Hyphae are made of tubular cells with rigid cell walls containing chitin

• Chitin is a polymer of N-acetylglucosamine

• Cell membranes contain ergosterol, not cholesterol

What is the difference and similarity between septate hyphae and coenocytic hyphae?

• septate (cross walls) or coenocytic (“common cytoplasm”) hyphae

• both allow rapid cytoplasmic streaming

How do hyphae feed? what do they secrete and why?

• Hyphae feed by absorbing simple organic compounds

• thus fungi are absorptive heterotrophs

• most secrete hydrolytic enzymes & acids

  • this digests organic materials

  • Fungi are mostly saprobes

  • Some fungi are parasitic, infecting either plants or animals

What are haustoria? What do they do?

• some specialized hyphae:

• haustoria penetrate cell walls of host plant without killing cell

What is the relation between nematodes and hyphae?

• some hyphae “catch” nematodes for Nitrogen!

During fungal reproduction, where do the reproductive bodies emerge from?

a mycelium to make spores

In what cycles are spores made and describe the process of fungal reproduction

• Spores are made in both sexual and asexual cycles

• one cell (haploid, n), protected by coating

• disperse by air/ water to new resources

• spores germinate on food source

• each grows into a new haploid (n) mycelium

How does the process of asexual reproduction with spores by mitosis work?

grow new genetically identical mycelia

What are the two types of asexual spores?

conidiospores, sporangiospores

What is a sporangium?

Spores may be released from the parent thallus either outside or within a special reproductive sac called a sporangium

What are the three different types of asexual fungal reproduction and describe them

• budding: a bulge forms on the side of the cell, the nucleus divides mitotically, and the bud ultimately detaches itself from the mother cell

  • Somatic cells in yeast form buds

• fragmentation: bits of mycelium can grow into new individual

• asexual spores: by mitosis, grow new genetically identical mycelia

When is sexual fungal reproduction called homothallic? When is it heterothallic?

• when both mating types are present in the same mycelium, it is called homothallic, or self-fertile

• Heterothallic mycelia require two different, but compatible, mycelia to reproduce sexually

For sexual fungal reproduction there are no genders so what are the two mating types?

(+) or (–)

What are the three steps to form a zygote in sexual fungal reproduction?

1. plasmogamy = fusion of haploid (+) & (–) hyphae

2. heterokaryotic stage = hyphae with unfused haploid nuclei of both types

3. karyogamy = fusion of +/– haploid nuclei to form zygote (2n)

How does sexual fungal reproduction make diverse spores?

• zygote (2n) always does meiosis, making genetically diverse spores (n)

  • (never a multicellular 2n stage)

Describe the generalized fungal life cycle

describe the fungus phylogeny, which ones are mostly terrestrial and which are mostly aquatic? At what point is the flagellum lost?

Chytrids: Describe them, their structure, how they are different from other fungi, and their role in the environment

• the simplest and most primitive Eumycota, or true fungi

• have chitin in their cell walls

• most chytrids are unicellular

• a few form multicellular organisms and coenocytic hyphae

• Chytrids are the only fungi that have retained flagella

• flagellated spores (zoospores) and gametes

• aquatic decomposers (saprobes) or parasites

Zygomycetes: describe them, their role, how they reproduce, and an example

• sexual cycle makes a resistant zygosporangium

• coenocytic hyphae

• most species are saprobes (an organism that breaks down dead or decaying organic matter for nutrients)

• a few are parasites, particularly of insects

• Usually reproduce asexually by producing sporangiospores

• EX: Rhizopus sp. bread mold

Ascomycota: The Sac Fungi, what are the two different types and give 3 examples

• sexual spores (ascospores) within saclike ascus (plural asci)

• asexual spores (conidiospores) are released by conidiophores

• EX: cup fungus, morel, Tuber melanosporum (truffle)

Basidiomycota: The Club Fungi, what type of spores do they have, what is its reproductive organ called, give an example

• sexual spores (basidiospores) within club-like basidium

• basidia, which are the reproductive organs of these fungi, are often contained within the familiar mushroom

• EX: common mushroom

Glomeromycota: what type of relationship do they have

• mutualistic arbuscular mycorrhizae

• 90% of plant species have a mycorrhizal relationship

Describe the growth and surface area of fungi

• rapid growth at hyphal tips toward new food (no motile feeding cells)

• huge total surface area for absorption

What is the importance of fungi?

• Fungi are Decomposers

• Fungi Damage Property

• Fungi are Mutualists

• Fungi are Pathogens

• Fungi Benefit Medicine & Research

• Fungi & Food

• Poisonous Fungi

How do fungi differ from bacteria as decomposers?

Many bacteria & fungi are great at decomposing cellulose, but most bacteria cannot break down lignin (fungi can!)

How do fungi damage property?

“Dry rot” & “wet rot” & “mold” & “mildew”

How are fungi mutualists?

• mycorrhizal fungi help plants absorb moisture & minerals

• fungus “gets” sugars, etc., from plant

What are the three types of mutualistic fungi and describe them

• Ectomycorrhizae

  • Fungus remains outside root and between cells

• Endomycorrhizae (arbuscular mycorrhizae)

  • fungi penetrate cell walls and form haustoria

  • All Glomeromycetes are endomycorrhiza

• Lichens

  • fungi living in close association w/ photosynthetic unicellular chlorophyte or cyanobacteria

  • fungus “gives” framework, moisture, minerals

  • algae/cyanobacteria “gives” sugar • can reproduce as “dual organism” via soredia

How are fungi pathogens to plants? what do they produce?

• Infecting plants:

  • attack trees, landscape plants, crops

  • e.g., rusts & smuts

• Several produce mycotoxins e.g., ergot – ergotism, LSD

• Claviceps purpurea causes ergot on rye, barley and other grasses

• Probable cause of St. Anthony’s fire

What type or neurological symptoms does fungus cause and how?

• Fungus produces alkaloid toxins that cause severe physiological & neurological symptoms

  • Hallucinations

  • Burning skin sensation

  • Bug crawling feeling

  • Gangrene due to vasoconstriction

  • Tremors

  • Still births

  • Abortion

How do fungi infect humans? what type of infections can it cause? which ones are treatable and which ones are severe?

• Infecting humans

  • mycosis = infection due to fungus

  • some very serious, difficult to treat

    • Ex: “valley fever” (coccidioidomycosis)

  • many common, treatable

    • Ex: ringworm, oral thrush, athlete’s foot, jock itch, vaginal yeast infections

How are fungi important in medicine and research? Give an example of a fungi used

• Source of antibiotics & other meds

  • Ex: penicillin, cephalosporins

• Genetic research & biotechnology

  • Ex: Neurospora research model organism

  • Dr. Bell-Pederson

  • Dr. Sachs

• Ex: yeasts

How do we use fungi in our food? Give examples of foods.

• Yeasts do fermentation

  • ethyl alcohol in beer, wine, etc.

    • CO2 for rising bread

• Molds used in food processing

  • Ex: bleu cheese, soy sauce

Give examples of poisonous fungi

• Moldy foods can kill humans, livestock!

  • Ex: ergotism from ergot on rye

  • Ex: aflatoxin from Aspergillus on corn, peanuts, etc

• Many mushrooms are deadly!

  • Never eat wild fungi!