Fungal Structure and Function

Regarding the mode of action of antifungal drugs, which one of the following is most accurate? Terbinafine acts by inhibiting fungal DNA synthesis but has no effect on DNA synthesis in human cells. Azole drugs, such as fluconazole, act by inhibiting ergosterol synthesis. Echinocandins, such as caspofungin, act by inhibiting messenger RNA synthesis in yeasts but not in molds. Amphotericin B acts by inhibiting fungal protein synthesis at the 40S ribosomal subunit.

Azole drugs, such as fluconazole, act by inhibiting ergosterol synthesis

What components of the fungal cell wall are unique to fungi only?

Chitin and glucan components of cell wall are unique & essential to fungi. These cell wall components have no mammalian counterpart and are the targets of antifungals.

The selective toxicity of amphotericin B is based on the presence in fungi of which one of the following? 30S ribosomal subunit Mycolic acid Ergosterol Dihydrofolate reductase DNA gyrase

Ergosterol

What are the components of the fungal cell membrane?

Ergosterol (main component), phospholipids, sphingolipids, membrane proteins

What are the fungal diseases?

Fungal nail infections Ringworm Vaginal candidiasis Oral thrush Histoplasmosis Blastomycosis Aspergillosis Pneumocystis pneumonia

What are Polyoxins?

Potent inhibitors of chitin synthases in fungi

What are the two general classes of fungal pathogens?

Primary pathogens (fungi that cause disease in non compromised patients Opportunistic pathogens (cause disease in hosts whose local or systemic immune system has been impaired, damaged, or is innately dysfunctional)

What are polyene antibiotics?

Produced by Streptomyces species fungicidal Broad spectrum

What is the fungal cell wall?

Provides structural support and protection to the fungal cell. Contains mainly chitin, glucans, and mannan in different proportions depending on the species.

What is the fungal cell membrane and the cell wall comprised of?

Sterols, mostly ergosterols comprises the fungal cell membrane chitin mannan, and glucan comprises the fungal cell walls

Regarding the structure and reproduction of fungi, which one of the following is most accurate? Molds are fungi that grow as single cells and reproduce by budding. Peptidoglycan is an important component of the cell wall of fungi. As most fungi are anaerobic, they should be cultured under anaerobic conditions in the clinical laboratory. The fungal cell membrane contains ergosterol, whereas the human cell membrane contains cholesterol. Some fungi are dimorphic (i.e., they are yeasts at room temperature and molds at body temperature).

The fungal cell membrane contains ergosterol, whereas the human cell membrane contains cholesterol.

What are the two major forms of fungi?

Unicellular forms (yeasts) Multicellular filamentous forms (molds)

What is chitin?

a long linear homopolymer of β-1,4-linked N-acetylglucosamine. Relatively minor, but structurally important, component of fungal cell wall. Chitin accounts for 1-2% of yeast cell wall by dry weight and 10-20% of the cell walls of filamentous fungi.

What is mannan?

a polysaccharide and polymer of the sugar mannose; highly immunogenic component of fungal cell wall.

Are fungi considered eukaryotes or prokaryotes?

eukaryotes

What is the mechanism of action for polyene antibiotics?

forms a complex with ergosterol in the plasma membrane, causing membrane disruption, increased permeability, leakage of cytoplasmic contentsØ, and ultimately cell death.

What is the function of echinocandins?

inhibit cell wall synthesis - inhibits β-1,3-D-glucan synthesis

What is ergosterol involved in?

involved in numerous biological functions: Membrane fluidity Regulation Activity and distribution of integral membrane proteins Cell cycle control

What is glucan?

major structural polysaccharide of fungal cell wall, constituting approximately 50-60% of the wall by dry weight. Polymers of glucan are composed of repeating glucose residues that are assembled into chains through a variety of chemical linkages. Between 65% and 90% of cell wall glucan is found to be β-1,3-glucan, which serves as the main structural constituent to which other cell wall components are covalently attached

What are the echinocandins?

semi-synthetic lipopeptide first-line agents for treating severe invasive fungal infections fungicidal against yeast and fungistatic against molds