Fungi 2023 Past Paper PDF

Cell Biology & Genetics. Fungi Dr Anna Black Learning outcomes By the end of this session you will be able to: 1 Characteristics 2 Structure 3 Fungi & disease 4 Reproduction (main groups) 5 Products (harmful &/or useful) Fungi  Kingdom (within domain of Eukaryotes) ...

Cell Biology & Genetics. Fungi Dr Anna Black Learning outcomes By the end of this session you will be able to: 1 Characteristics 2 Structure 3 Fungi & disease 4 Reproduction (main groups) 5 Products (harmful &/or useful) Fungi  Kingdom (within domain of Eukaryotes)  Nearly all multicellular (yeast uni)  Diploid number of chromosomes and membrane bound nucleus  MYCOLOGY - study of fungi Fungal Cell Wall Characteristics: HETEROTROPHS Need to obtain carbon from another organic source Nutrition of Fungi  Acquire nutrients by absorption  Most are saprophytes  Some are parasites  Some are symbiotic  Most aerobic – some facultative. Morphology 1) Yeast (A,B,C) 2) Hyphae (D,E,F) STRUCTURE OF FILAMENTOUS:  Multinucleate  branched filaments (hyphae), forming a mycelium  Non-reproductive structures collectively called thallus  moulds  filamentous fungi HYPHAE:  Chitin wall (polymer: N-acetylglucosamine)  Typically 5-30 m diameter  Grow from tip (apical growth)  No fixed length (>100 metres in soil)  Branched - 2D or 3D growth Did you know… The largest known organisms is a fungi? Hyphae:  Not composed of ‘standard cells’  Multinucleate compartments  Coenocytic form [“common cell”] – where cytokinesis doesn’t occur despite multiple nuclear division  Cross-walls [SEPTA] have pores cytoplasm Nuclei may pass through pores in septa Where would you expect to see hyphal forms of fungi? Hyphae aggregate [visible]:  on surface of substrate (mould = growing mycelium)  ‘fruiting bodies’ (mushrooms & toadstools) Mycelium on food Mycelium on leaf –ash dieback disease Mycelium on skin (“ringworm”) 1) MOULDS - filamentous fungi:  Mostly AEROBES (respiratory metabolism)  Major DECOMPOSERS of biopolymers (soil/water)  Mostly harmless (necrotrophs) ….. few pathogens (biotrophs) 2. YEASTS – non filamentous  Unicellular fungi  Grow by (i) budding or (ii) fission Saccharomyces - a budding yeast Budding [asexual reproduction] Saccharomyces - a budding yeast scanning electron micrograph bud scars 10 micrometres Saccharomyces cerevisiae Schizosaccharomyces - a fission yeast Schizosaccharomyces pombe Fungal Cell Wall Yeast cell structure:  Most organelles in animal cells also found in yeast cells  e.g. nucleus, ribosomes (80S), mitochondria, endoplasmic reticulum, Golgi body, etc.  Cell wall is major additional feature Yeasts: culture  COLONIES on agar media  Slower growth than many bacteria (doubling time 2-3 h)  Colonies take 1-3 days to form Pathogenic fungi and how we fight them! Fungi and DISEASE - Mycosis  Azole class – Inhibit fungal ergosterol biosynthesis lanosterol 14  demethylase H H H HO HO lanosterol ergosterol N N N N N N HO F Fluconazole F Image from doctorfungus.org Effect of azoles on C. albicans  Polyene class - Amphotericin B OH O OH OH HO O OH OH OH OH O O H OH O O Amphotericin B HO OH NH 2 Image from doctorfungus.org DIMORPHIC FUNGI Both cellular forms!!! DIMORPHIC fungi:  Two structural phases: 1 yeast phase (unicellular) or 2 filamentous phase (hyphae) Candida albicans … dimorphic fungus Candida albicans - dimorphic fungus germ tubes - early transition phase germ tubes (light micrograph) Appearance of germ tubes in 2h @37°C in horse serum used in Candida albicans:  Dimorphism & pathogenicity  Commensal: yeast phase (e.g. mouth)  Invasive pathogen: filamentous phase REPRODUCTION BY SPORES  May be ASEXUAL or SEXUAL  Spore structure:  (1) nucleus  (2) dehydrated cytoplasm, (3) glycogen & (4) thick spore wall  Usually coloured - survive in sunlight (air dispersal)  Asexual spores – two main types 1 Individual spore - CONIDIUM (pl. conidia)  On aerial hyphae (CONIDIOPHORES)  Released into air  Diagnostic for particular fungi Penicillium - conidia Aspergillus - conidia http://www.wellcome.ac.uk/stellent/groups/corporatesite/@msh_publishing_group/documents/image/wtd028112.jpg Asexual spores - two main types 2 Multiple spores in a sac (sporangium) SPORANGIOSPORES  On aerial hyphae (sporangiophore)  Released into air: sporangial wall splits Sporangiospores - Rhizopus sp. Asexual reproduction:  IMPERFECT fungi only asexual spores  PERFECT fungi (also) capable of sexual reproduction (sexual spores)  Sexual spores – many different types … 3 main groups….. 1 ZYGOMYCETES  Sexual reproduction: fusion of hyphae from two individuals: ZYGOSPORE  Zygospore develops thick resistant wall  e.g. Mucor (bread mould) Zygomycete on solid media 2 ASCOMYCETES  Also known as sac fungi  Sexual spores in sac-like ASCUS  Eight ASCOSPORES per ascus  Ascus bursts open to release ascospores into air 3 BASIDIOMYCETES  Sexual spores on specialised cell (BASIDIUM)  Four BASIDIOSPORES per basidium  Released into air on maturation Basidiomycetes:  The most complex fruiting bodies are seen in basidiomycetes  (mushrooms and toadstools) PRODUCTS PRODUCTS Toxins (mycotoxins)………..  Ergot (Claviceps purpurea in cereals): alkaloid toxin related to lysergic acid diethylamide  Aflatoxins (Aspergillus flavus) stored foods Liver damage necrosis /cirrhosis and carcinoma  Amanita phalloides - ‘death cap fungus’  Psilocybin – magic mushrooms Products…  Antibiotics (antibacterial) …………..  penicillin (from Penicillium)  cephalosporin (from Cephalosporium) Products…  Foodstuffs……………..  mushrooms (Agaricus)  quorn (Fusarium)  Citric acid (from Aspergillus)