lecture 33-36 conceptrual stuff AI

What domain do fungi belong to and what are their basic characteristics?

Fungi are eukaryotic heterotrophs. They are non-motile and non-photosynthetic.

What are saprobes and why are fungi important as saprobes?

Saprobes are heterotrophic organisms that feed on dead organic matter (rotting wood, compost, etc.). Fungi are the key to recycling nutrients in ecosystems.

What are the beneficial uses of fungi? (industrial and scientific)

Industrial: soy sauce, cheese, beer, wine production.

Scientific: model system for understanding higher eukaryotes — used to study cell growth, cancer, and peroxisomes (affiliated with Zellweger's syndrome). Many biological processes are conserved between fungi and humans.

What are the harmful aspects of fungi?

Some fungi are parasitic and cause major diseases in plants and animals.

What are the 2 key components of the fungal cell wall?

Chitin and glucan — both are targets for antifungal drugs.

What is ergosterol and why is it important?

Ergosterol is the lipid in fungal plasma membranes that provides fluidity — it plays the same role as cholesterol in human cells. Because it's unique to fungi, it is a key target for antifungal drugs (selective toxicity).

What pH environment do fungi prefer and how can you exploit this?

Fungi prefer a moderately acidic environment. Adding a base (alkaline substance) to mold can kill it.

What is absorbitive nutrition in fungi?

Fungi secrete digestive enzymes to the outside of their cells, break down food externally, then absorb the digested nutrients into the cell. They cannot engulf food like animals.

What is a thallus?

The fungal body — the entire physical structure of a fungus.

What are the two basic structural forms of fungi?

Yeasts (unicellular) and molds (multicellular).

What is a dimorphic/biphasic fungus?

A fungus that can exist as either a yeast or a mold depending on conditions. The switch between forms is triggered by temperature.

What is a hypha (plural: hyphae)?

A filament of fungal cells stuck together end-to-end — the basic structural unit of a mold.

What is a mycelium?

A thick, tangled mass of hyphae — the visible "body" of a mold. Cells are connected by holes/pores between them.

What is the difference between coenocytic and septate fungi?

Coenocytic fungi: no septa (cross walls) — cells are not divided, forming one continuous multinucleate mass. Septate fungi: individual cells separated by cross walls (septa) that have pores connecting adjacent cells.

What is the preferred ploidy state of fungal cells?

Haploid — single, unpaired chromosomes. Fungi prefer the haploid state.

What are the two modes of reproduction in fungi?

Asexual and sexual reproduction.

How do yeasts reproduce asexually?

By fission (equal split into two equal daughter cells) or budding (one smaller daughter cell buds off from the parent).

What are sporangiospores?

Asexual mold spores created inside a specialized covering structure called a sporangium, located at the end of hyphae. The sporangium is a protective "sack."

What are arthrospores/arthroconidia?

Asexual mold spores with NO specialized structure — any area of the hypha can break off and grow into a whole new mycelium. "Arthro" = joints, like breaking at the joints.

What are conidiospores?

Asexual mold spores produced from a specialized structure called a conidiophore, but the spores are NOT covered/protected (unlike sporangiospores). The conidiophore is exposed ("Conan the Barbarian" — no protection).

What is a mycosis?

A fungal disease.

Why are there so few antifungal drugs compared to antibiotics?

Because fungi are eukaryotes — they share many cellular structures with humans (60S and 40S ribosomes, ER, etc.), making it very difficult to achieve selective toxicity. Drugs that kill fungi tend to also harm human cells.

What is the main structural target that antifungal drugs exploit for selective toxicity?

Ergosterol — found only in fungal plasma membranes (not human cell membranes). Also chitin and glucan in the fungal cell wall (absent in human cells).

What are Polyenes and how do they work?

A class of antifungal drugs with multiple double bonds that target ergosterol in the fungal plasma membrane. They bind to ergosterol and form pores → excessive leakiness → cell death.

What is Amphotericin B and when is it used?

A polyene antifungal — the gold standard for systemic (body-wide) mycoses. Given by IV because it targets ergosterol and creates pores in fungal membranes.

What is Nystatin and when is it used?

A weaker polyene antifungal used for topical (surface) mycoses — not used systemically. Same pore-forming mechanism as Amphotericin B.

What are Azoles and how do they work?

A class of antifungal drugs that interfere with ergosterol SYNTHESIS — they inhibit the enzymes that produce ergosterol. Without ergosterol, the membrane becomes leaky and the cell lyses.

Name two Azole antifungal drugs and their uses.

Miconazole: found in over-the-counter antifungal products.

Fluconazole: a prescription antifungal drug. Both block ergosterol biosynthesis.

What are Allylamines and how do they work?

A class of antifungal drugs that affect a different enzyme step in ergosterol biosynthesis than Azoles. Example: Lamisil (terbinafine). Result is the same — impaired ergosterol production → membrane dysfunction.

What are Echinocandins and how do they work?

Antifungal drugs that target glucan synthase — the enzyme responsible for glucan synthesis in the fungal cell wall. Without glucan, the cell wall is weakened → cell lysis. Example: Caspofungin. Analogous to how penicillins/cephalosporins target bacterial cell wall synthesis.

How are Echinocandins analogous to penicillins?

Both target cell wall synthesis enzymes — Echinocandins block glucan synthase in fungi; penicillins block transpeptidase in bacteria. Both result in weakened cell walls and lysis.

What is Griseofulvin and how does it work?

An antifungal that deactivates tubulin → blocks microtubule assembly → prevents chromosome separation during mitosis → fungal cells cannot divide. Used mainly for skin and nail infections because it concentrates in epithelial cells.

Why is Griseofulvin used specifically for skin and nail infections?

It concentrates in epithelial cells and in fungi that infect those cells — achieving sufficient local concentration to be effective.

What is Nikkomycin Z and how does it work?

An antifungal still in development. It inhibits chitin synthase → weakens the fungal cell wall → lysis. Has high selective toxicity with few side effects. Specifically used for Valley Fever.

What is Valley Fever?

A fungal disease specifically targeted by Nikkomycin Z (still in development).

Why does Nikkomycin Z have high selective toxicity?

It targets chitin synthase, which is needed to make chitin — a component of fungal cell walls that is completely absent in human cells. Humans have no chitin synthase to inhibit.

Compare all 4 main antifungal drug classes by their target.

Polyenes (Amphotericin B, Nystatin): bind ergosterol → pores in membrane.

Azoles (Miconazole, Fluconazole): block ergosterol synthesis.

Allylamines (Lamisil): block different step in ergosterol synthesis.

Echinocandins (Caspofungin): block glucan synthase → weaken cell wall.

Griseofulvin: blocks tubulin/microtubules → stops mitosis.

Nikkomycin Z: blocks chitin synthase → weaken cell wall.

What is a protozoan?

A unicellular eukaryote with organelles. Found in moist habitats. Most lack chlorophyll. Mobile during at least some phase of their life cycle.

How are protozoans different from fungi in terms of cell structure?

Protozoans DO NOT have cell walls — this is a key distinction from fungi (which have chitin/glucan cell walls) and bacteria.

What makes protozoans more complex than bacteria or fungi?

They are eukaryotes with organelles, have multiple nuclei, undergo many developmental changes in their life cycle, and take longer to replicate.

What is a pellicle in a protozoan?

A belt of protein located outside the plasma membrane. It is rigid but contractile — useful for squeezing between tight spaces (e.g., between cells).

What are contractile vacuoles in protozoans?

Organelles that expel or take up water — used for osmoregulation (water balance).

What are the two life forms of a protozoan?

Trophozoite: the active, feeding form — the protozoan is happy and eating. Cyst: the dormant form — triggered when the environment is bad or food is scarce. Similar to a bacterial spore.

What triggers a protozoan to form a cyst?

Adverse environmental conditions — bad environment, running out of food. The protozoan encysts to survive.

What triggers a protozoan to exit the cyst (excystation)?

Return of moisture and nutrients — favorable conditions cause the cyst to reactivate into the trophozoite form.

How is a protozoan cyst analogous to a bacterial spore?

Both are dormant, resistant forms that form in response to environmental stress and can reactivate when conditions improve.

--- COMPARISON: Fungi vs. Protozoans ---

--- Key distinctions between these two eukaryotic microbe groups ---

Are fungi and protozoans both eukaryotes?

Yes — both are eukaryotic, unlike bacteria (prokaryotes).

Do fungi or protozoans have cell walls?

Fungi: YES — cell wall made of chitin and glucan. Protozoans: NO cell wall. This is a major structural difference.

Are fungi or protozoans motile?

Fungi: NON-motile. Protozoans: MOTILE during at least some phase of their life cycle.

What membrane lipid do fungi have that humans don't?

Ergosterol — the basis for antifungal selective toxicity. Protozoans and humans use cholesterol instead.

What dormant forms do fungi vs. protozoans produce?

Fungi: spores (sporangiospores, arthrospores, conidiospores). Protozoans: cysts (analogous to bacterial spores — dormant, resistant, reactivate when conditions improve).

What is the nutritional strategy of fungi vs. protozoans?

Fungi: absorbitive nutrition — secrete enzymes outside the cell, digest food externally, absorb products. Protozoans: most are heterotrophic but can engulf food directly (no external digestion required).