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Human Biology
James Scott

HMB436 Midterm Notes Lecture One  Fungi are a kingdom  One of the several highest domains of life  They have very varied morphology  Termitomyces titanicus is a huge mushroom while penicillium digitatum is microscopic  Cordyceps militaris feeds on pupating beetles; it grows through the pupal case and out of the beetle  There are three groups in the tree of life o Archaea, bacteria, and eukarya o Fungi are eukarya; humans are more related to fungi than fungi are to plants  There are three main lineages of fungi that will be focused on in this course o Muoromycotina also referred to as zygomycota/zygomycotina o Chytridiomycota o Dikarya (subdivided into basidiomycota and ascomycota)  Microsporidia is a new lineage of fungi; parasitic and unicellular species  Species within each class are phenotypically diverse; however, they have similar growth patterns  Most fungi are filamentous (hyphae)  Each hypha (singular) has several organelles and membrane-bound mitochondria ; it is possible for them to be multinucleated or have multiple mitochondria  Cell wall composition o Oomycota (not phylogenetically related; it is more of an algae however it behaves like a fungus; this explains difference in cell wall chemistry- more similar to plant)  Fibrillar components  cellulose, beta 1,3/1,6-d-glucans  Matrix components  glucan o Chtrydiomycota  Chitin, glucan  Glucan o Zygomycota/mucromycotina  Chitin, chitosan  Polyglucuronic acid , Glucuronomannoproteins o Ascomycota  Chitin, beta 1,3/1,6-d-glucans  Alpha 1,3-d-glucan, galactomannoproteins o Basidiomycota  Chitin, beta 1,3/1,6-d-glucans  Alpha 1,3-d-glucan, xylomannoproteins  Fungi are heterotrophic o Means they cannot fix carbon o Use organic carbon for growth o Opposite of autotrophs like plants and algae which can use energy from sunlight or inorganic compounds to make carbon compounds  Fungi digest their food OUTSIDE their cells  The hyphae absorb nutrients from the environment and release metabolites and antimicrobial materials o The hyphal type is the meristem where the fungi grows from (meristem is pool of stem cells) o The cell wall matrix of the hyphal tip is very porous which allows enzymes to be secreted and nutrients to be taken in. o The enzymes are secreted in order to breakdown the nutrients that are in the extracellular space; they are then taken up and metabolites are subsequently released  Hyphal structure o Septum  assues connection between hyphal cells ; permits movement of cytoplasm between adjacent cells o Ascomycota  single haploid nucleus and septum with one hole; also has woronin body  Woronin body is near septum and divides hyphal compartments; plugs septal spores after hyphal wounding which restricts loss of cytoplasm o Zygomycota  none, or very few septa (number of holes can be many or little), multinucleated (coenocytic)  Filamentous growth o A fungus can start as a single spore and branch because of germination o Radial growth allows for rapid colonization of surfaces  This is good for terrestrial surfaces but not good for fluids  Enzymes are secreted at fungal tips would float away in fluid  Adaptation to things they can do in fluid  Yeast have a more flexible cell wall which allows for more surface area; they bud to disperse throughout the fluid  A blob of filaments is called a mycelium; they are propagative structures  Fungi can grow in many forms o Yeast grows by budding  Spores o Spores can arise sexually (from meiosis)  Ascospores, basidiospores, zygospores o Can also be asexually reproduced  Sporangiospores in zygomycota  Always produced internally in a sporangium  Conidia in Ascomycota and some basidiomycota  Conidia are hyphae that have become modified through evolution for dispersal purposes  Always produced externally on a conidiophore  Sexual Reproduction o Most fungi are vegetative (non-reproductive) haploids (vegetative state also referred to as somatic)  Few are diploid (e.g. yeast candida albicans) o Each mycelia will carry a compatible nucleus (haploid) that will fuse (anastomosis)  Sometimes will become a dikaryon once compatible haploid nucleus is received  Nuclei then either undergo meiosis or continue to grow and mate later  The Ascomycota usually undergo meiosis immediately  The basidiomycota mycelium usually continues to grow (somatically) and will mate later  *anastomosis is the fusion between branches of the same or different hyphae; this allows for two different haploid mating types (merge if compatible)  We have the most complete taxonomic knowledge on animals and one of the least for fungi, insects, bacteria, and viruses – probably because there are so many types compared to mammals  Chytridiomycota o Mostly aquatic (FRESH WATER mostly) o Saprotrophic, meaning they grow on dead things o Some are parasites of plants (roots, pollen grains etc) o If you sprinkle pine pollen on pond water, chydridiomycota will colonize them o Some examples  Synchytrium endobioticum (potato wart disease)  Batrachochytrium dendrobatidis (amphibian decline)  Zygomycota/mucoromycotina o If you leave sugary fruit on the counter, contain will grow filaments (rhizopus) o Hyphae mostly lack septa and cells are multinucleated (coenocytic) o Includes 5 phylogenetic groups  Mucormycotina  Mostly saprotrophic but some parasitic  Contribute most to human disease  Grow fast  Like sugar (simple)  Some like high temps  Entomophthoromycotina  Sophisticated insect pathogens; usually venereally transmitted  Grows in insect cavity and causes behavioural changes (attraction to light, lying on its back, causing the zygospore cell wall to thicken)   Glomeromycotina  Symbiotic with plant roots  Reproduction in zygomycota o Sexual zygospores  2 compatible gametangia meet, grow apart, then grow towards each other and anastomose  Their nuclei move to central cell which becomes a zygosporangium which contains a single zygospore  Gametangia that are left empty are called suspensors o Asexual reproduction sporangiospores  Born inside sporangium  Can be single or multiple  Hyphae have sporangiospore in bulb tips which are the sporangium  These spores build up anre burst, spreading themselves out  the base of columella is a very light sensitive area  favours growth towards light; pressure builds up and sporangium bursts and releases spores  basidiomycota o sexual reproduction by basidiospores  produced EXTERNALLY on basidium o mostly larger fungi o mushrooms are the sexually reproducing ones o septa always have a central pore o asexual reproduction by conidia (modified hyphae), yeasts (but many lack asexual forms)  conidial e.g. sporotrichum  yeast e.g. sporomolomyces and Cryptococcus  can produce vegetative dikaryon  dikaryotic hyphae usually have clamp connections; o clamp connections are necessary to grow two different nuclei without recombining them in the same cell; same orientation maintained in compartments  the hyphae are always separate  a lot are saprotrophic; esp cause wood to rot  others are plant symbionts or parasites  Ascomycota o Sexual reproduction by ascospores  Produced inside ascus o Sister to basidiomycota o Generally smaller though o Ascus grows inside or on the ascoma o Commonly called cup fungi  Floppy cup like fruiting bodies called apothecia o More of the species make whisker like asomas  Ones with necks  perithecia  Ones that are entirely closed are called cleistothecia  Ones like tumbleweeds are called gymnothecia o Asexual cells line the interior of the cup (fertile portion) called hymenium o When they form a dikaryon, it never continues to grow  Only exist as vegetative monokaryons  Never have clamp connections o Asexual  By mitotic spores (conidia)  Often highly specialized  Some only make conidia – e.g. moulds o Vast ecological diversity – saprotrophic, parasitic, mutualistic… o Some are so successful producing asexually that they stop producing sexually o Asexual were classed under deuteromycotia, class hyphomycetes  Sexual stages are called telemorphs while asexual stages are called anamorphs Lecture One Readings Notes  Fungi are unicellular or multicellular and are eukaryotic and heterotrophic  Fungi have rigid cell walls; chitin/glucan/cellulose  Any fungus capable of growing at 37 Celsius is a potential pathogen in a debilitated or immunocompromised host o Note: some are pathogens and can cause disease in hosts with normal immune systems  Severity of disease relates to host factors, number of spores, and method of entry  Ubiquitous in nature – found everywhere  There is no part of our earth where fungi are not found  With a few exceptions, most fungal pathogens invade humans accidentally  Most fungi with pathogenic potential are opportunistic  Mycoses are diseases of humans and lower animals caused by pathogenic fungi  Fungi were the first microorganisms known  Vast majority of fungal infections are not spread from person to person o Exceptions: favus  The first cure of metastatic cancer was obtained in 1956 when methotrexate was used to treat a rare tumour called choriocarcinoma  Cancer chemotherapy which weakened the immune system made opportunities for yeast and mold disease o Mainly candidiasis and aspergillosis  AIDS also caused immune system weakening and therefore more prone to fungal infection  Important milestones in mycology o More rapid tests to identify candida species o Wider availability of antifungal tests o Transfer of technology into the clinical lab for sequence based identification  Simplest fungi are yeasts o Unicellular o Budding /fission o Blastoconidia cause disease in humans o Trichosporon buds and has hyphae o A lot of yeasts have pseudohyphae – when blastoconidia remain attached in a chain of round to elongate cells – string of pearls  Molds o Formed by filamentous, cylindrical, branching cells called hyphae o Mass of hyphae is mycelium o Hyphae have two different forms  Zygomycota vs. basidiomycota (see above)  Vegetative growth is necessary but not sufficient to spread fungus  Dikarya is the largest category Lecture two  Cell wall chemistry o Hyphal tip is at distal end; this is the end that the hyphae is growing at o Proximal composition (not exactly hyphal tip), so the older part of the fungus  Mostly carbohydrates and proteins  Chitin is the principle fibrillar cell wall protein  See polysaccharides table o Different stages of the fungus can be chemically different  Yeasts, spores, hyphae, and sporangiophores can be chemically different in the same species  DNA and RNA o Genome size of fungi is more than bacteria but less than higher eukaryotes  10-60MB; average 37 o Largest genome is scutellospora castanea (795) o Smallest genome is pneurnocystis carini (7) o Mass based content of DNA in fungi is lower than other organisms  Because stuff that is not DNA has much more mass relatively  High cell wall material  Metabolism o Catabolism  Energy taken from nutrients to make energy for anabolic reactions  ATP NADH NADPH  Key for macromolecules of hyphal structures o Anabolism  Nutrients changed into structural and functional components of the cell  Dependent on catabolism  Aerobic respiration o Regeneration of NAD+ by transfer of electrons to oxygen under aerobic conditions o Fungal respiration similar to other eukaryotes o Take place mostly in mito o Converts molecules into ATP (catabolic) o In cases of oxidative stress, undergo fermentation to generate NAD+ in the absence of O2  Fermentation o Regeneration of NAD+ by transfer of electrons to pyruvate under anaerobic conditions o Lack of O2 means oxidative phosphorylation cannot produce ATP by glycolysis  In the presence of O2 some fungi still prefer fermentation  Alcoholic fermentation (fungi) o Conversion of pyruvate to ethanol and CO2  Lactic acid fermentation o Other eukaryotes o Pyruvate to lactic acid o Mostly zygomycota (can do both)  Both pathways clear pyruvate and regenerate NAD+ o This is still aerobic respiration because O2 is still the electron acceptor  Trehalose o Alpha linked diglucose o Common in fungi, some bac and plants o Storage/energy o Important for signalling during periods of stress o Some people cannot digest it
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