PMB: Mycology Flashcards
What are characterisitcs of fungi?
- Eurkaryotes
- Multiple Chromosomes
- DO NO all look the same - come in different shapes and structures
- Microscopic organisms
- Possess a nucleus
- Often Fast growing
- Can be harmful e.g. produce contaminants or beneficial e.g. source of AB
Medically, which fungi are most important?
Yeast and filimentous
Discuss the structural characterisitics of fungi
- Fungi all have a cell wall, made of polysaccharide. Mainly B-glucan with mannan and chitin
Describe fungal growth
- Optimum growth temperatures for medically important fungi are between 20-25C
- Fungi have complex reproductive strategies
- Growth includes vegetative cycles and spore formations. Vegetative cycles tends to occur when their is a rich supply of nutrients. Where as spore foramtion tends to be a strategy to allow an organism to persit under harsh conditions
- Both sexual and asexual reproduction can occur. Asexual growth allows the organisms to divide rapidly during favourable conditions. However sexua; growth allows for diversity in a chanign ecosystem. Sexual growth can still occur during favourable conditinos
Discuss the characteristics if yeast
- unicellular spherical fungi
- Faculative anaerobes
- Asexual and sexual examples
- diameter around 10um
- What are examples of yeast and their uses:
- What methods of asexual reproduction do yeast undergo?
- g
- Binary fission or Budding:
- Binary fission - the parent cell splits into 2 approx equally sized daughter cells
- Budding - A smaller daughter cll budding off from the parent cell
Describe and explain the appearance of filamentous fungi
- Filamentous fungi have a fury appearance due to the hyphal growth of filamentous structures.
- These are called hyphae and can grow several cms.
- They form a complex mass called the mycelium
What does mycosis means? What classes is there?
- Fungal infection.
- Fungal infections can be split into 3 further categories depending on location of the infection:
- Superficial
- Cutaneous or subcutaneous
- deep
What are superifical mycosis? Examples
- Occur on the surface of skin
- Candidiasis
- Tinea (ring worm)
What are cutaneous or subcutaneous mycosis?
- Fungal infections beneath or within structures e.g. skin, hair, nails
What are deep mycosis? examples
- Fungal infections within the body
- aspergillosis (farmers lung)
Why would ABs and general anti-eukaroyte compouds be useful in treating mycosis?
Fungi are Eukaroytes, ABs are used for prokaryotic cells.
Mammal cells are also eukaryotes, therefore they might effect/ harm human cells
What compounds would be useful for treating fungal infections and why
Though mammal and fungi cells are both eukaryotes they do contain some differences e.g. cell walls and membranes, In Human membranes there is cholsterol, where as in fungi cells there is ergosterol (a derivative of cholseterol).
Ergosterol is present in large concentrations in the fungi membranes and is thought to be essential to their survivial. Therefore any compound which inhibits its synthesis could be an antifungal.
However, got to be careful to target synthesis of E. Many steps of E and C synthesis are the same.
What are cellular features of fungal cells which antifungals could be used to target?
- cell wall
- cell membrane
What are the main groups of antifungals
Polyenes
Azoles
Echinocandins
Allylamines
Describe some properties of polyene anti-fungals
- Polyunsaturated organic molecules
- 3 or more alternating C=C and C-C bonds
- Many hydroxyl groups
- Large macrolide latone ring
Uses of polyenes and problems
Many used in medical treatment against fungal pathogens.
However prolonged use leads to renal problems therefore reserved for serious systemic infections
Give an example of a polyene and its mechanism of action
- Amphotericin B is ampoteric and has both polar and non-polar regions, which helps with solubility in fungal membranes
- Amphotericin B is active and binds to ergosterol. It makes the membranes less in tack and porous. This causes leakage of molecules, mainly intracellular cations
Describe the structure of Azoles
- Heterocyclic compounds
- Contain a 5 membered ring
- Contains at least one N atom
- Also contains at least 1 other non-carbon atom within the ring
What is the mechanism of azoles? examples of Azoles
- Azole dervivatives are widely used as anti fungal agents e.g. ketonazole or Flucanazole
- Azoles inhibit ergosterol synthesis
- They bind to lanosterol 14a-demethylase. This prevents demethylation of lanosterol. This failure to demehylate means less ergosterol is produced which makes the membrane less stable. In turn this makes the mmebrane more porous. IT also allows for accumulation of toxic intermediates in the fungal membrane
Disccus the mechanism of action of allylamines and their composition
Have the chemical composition of C3H5NH2
Allkylamine derrivatives are also able to inhibit egosterol synthesis by inhibiting squalene monooxygenase
Describe thexhe structure of Echincandids
Semisynthetic lipoproteins which contain a cyclic hexapeptide rnig attached to a FA
New antifungal class
What is the mechanism of action of echincandids?
Inhibtis enzyme B-1,3-glucan synthase. this prevents synthesis of B-1,3-glucan which forms a major part of the cell membrane. Absence of this leads to osmotic instability and cell lysis
What are examples of intracellular antifungals and theri mechanisms
- Flucytosine is a synthetic fluorinated pyrimidine
- Derived from cytosine
- Interferes with nucleic acid and protein synthesis
- Griseofulvin is a compound which binds to microtubules (units of tubulin)
- Interferes with mitotic spindle
- Blocks fungal mitosis
