L20 - A Carmichael - characteristics of fungi Flashcards
are fungi eukaryotyes?
yep
do fungi have a cell wall?
yep - polysaccharide
how do fungi reproduce?
form spores
Most fungi feed on …
Most fungi feed on dead plant material
Fungi are eukaryotes that have - 3 characteristics
- a membrane-bound nucleus containing several chromosomes
- genomic DNA that contains exons and introns (a typical yeast cell has about 6000 genes)
- a plasma membrane and cytoplasmic organelles
in fungi, cell membranes contain what molecues?
cell membranes contain steroid molecules called ergosterols
describe the fungal cell wall strucutre
mainly composed of polysaccharides (a glucan = a polymer of glucose residues; a mannan = a polymer of mannose residues).
inner layer of chitin microfibrils (chitin consists of long straight chains of β-1,4- linked N-acetylglucosamine residues)
outer layer of glucans (branched chains of β- 1,3-linked glucose residues) in which are embedded a variety of glycoproteins
label - fungal cell call wall structure
label fungal morphology
describe Yeasts
oval or round unicellular organisms that multiply by mitosis
2 types of mitosis yeasts undergo?
either symmetrical binary fission (e.g. Schizosaccharomyces pombe)
or asymmetrical budding (e.g. Candida, Cryptococcus)
Some yeasts can also form short cylinders called ________ (e.g. Candida)
Some yeasts can also form short cylinders called pseudohyphae (e.g. Candida)
describe Filamentous moulds
Filamentous moulds consist of a hypha (plural hyphae) which is a thin branching multicellular cylinder.
D: hypha
a thin branching multicellular cylinder
can hypha differ in form. strcuture?
A hypha can be septate in which a septum (partition) separates adjacent cells into interconnected compartments (e.g. Aspergillus); or aseptate in which there are many nuclei in a common cytoplasm (e.g. Mucor).
how to hypha continue to grow?
Hyphae exhibit apical growth by mitotis at the tip (apex) or at side branches
Hyphae can form an interwoven mass called a ______; when compacted together, layers of hyphae can form fungal tissue in macroscopic structures e.g. mushrooms.
Hyphae can form an interwoven mass called a mycelium; when compacted together, layers of hyphae can form fungal tissue in macroscopic structures e.g. mushrooms.
what are dimorphic fungi?
Describe symetrical binary fission of yeasts
describe asymmetrical budding
for hypha where does branching occur?
behind the tip
Fungi produce _____ ( to reproduce by)
Fungi produce spores
what are fungal spores
small tough light fungal cells that are adapted for dispersal to new habitats and/or survival in hostile environmental conditions.
characteristics of spores
thick walled
high energy content
low metabolic rate
low moisture content
Depending upon specific environmental conditions, a given fungus can exist in one of two states of differentiation, namely asexual or sexual, which determines how the spores are produced:
what are they
Asexual reproduction – spores produced by mitosis
Sexual reproduction – spores produced by fusion of two gametes
describe asexual reproduction
sproes produced by mitosis
- Yeasts produce internal endospores.
- others produce external spores called a conidium (plural condidia) on the outside of a hypha
- others produce internal spores inside a special hypha called a sporangium
asexual spores are for dispersal
One group of fungi called ________ (also called imperfect fungi) always exist in the asexual state and are incapable of sexual reproduction.
One group of fungi called Deuteromycota (also called imperfect fungi) always exist in the asexual state and are incapable of sexual reproduction.
describe fungi sexual reproduction
unlike humans - most fungi exist an a haploid state
spores join, followed by mitosis to restore haploid chromosome number - to form new spores
Sexual spores are usually tough and enable the fungus to survive in hostile environmental conditions until more favourable conditions develop in which they can germinate.
The classification of fungi is based on what?
The classification of fungi is based on the three ways in which different fungi form their sexual spores.
3 categories for the classification of fungi based on sexual spore formation
Ascomycota form sexual spores within an internal tubular structure called an ascus.
Basidiomycota form sexual spores on an external specialized club-like structure called a basidium.
Zygomycota form sexual spores by fusion of specialized sexual hyphae.
whats special about Deuteromycota
no sexual spores - asexual spores only
describe hoew fungi obtain nutrition
- secrete enzymes into immediate environment for extracellular digestion
- absorb small molecules throgh channels in fungal cell wall
- rely on exogenous preformed organic compounds
Yeasts generally live in ____ environments
Yeasts generally live in moist environments;
Yeasts generally live in moist environments; the hyphae of moulds can penetrate into s…
Yeasts generally live in moist environments; the hyphae of moulds can penetrate into solid food material.
Many fungi are _____ that feed on dead plant or animal material.
Many fungi are saprotrophs that feed on dead plant or animal material.
cool picture
fungi are near the bottom of the food chain
true
label
guve some contributions of fungi to society
Pros
- Food (bread, Quorn)
- Beverages (beer)
- Antibiotics & drugs
- Recombinant proteins
- Scientific knowledge
Cons
- Damage to buildings & food
- Damage to living crops and trees
- Diseases of living humans & animals
Host defences against fungal infections
whats the importance of the commensal bacterial flora in the mouth and gut?
inhibits the multiplication of fungi on the epithelial surface as result of low-grade biological warfare between resident bacteria & competing fungi. Treatment with broad-spectrum antibiotics temporarily reduces the commensal bacterial population and permits overgrowth of commensal fungi such as Candida albicans.
Invading fungi are recognized by ….
Invading fungi are recognized by evolutionarily conserved pattern recognition receptors which act as microbial sensors
many of the pattern recognition receptors that recognize fungi are…..
many of the pattern recognition receptors that recognize fungi are lectins
what are lectins
(a lectin = a protein which has a carbohydrate recognition domain that specifically binds to a defined carbohydrate structure).
Pattern recognition receptors for fungi can be where? plasma? or intracellular?
Pattern recognition receptors can either be soluble in plasma (e.g. mannose binding lectin which activates the Complement enzyme cascade),
or on the surface/internal compartments of dendritic cells, macrophages, neutrophils and some epithelial cells.
label the molecules PRRs bind to
does MBL activate the complement system
yep
which Two rare autosomal recessive inherited disorders have been described in humans in which a loss-of-function mutation that impairs sensing of fungal β-1,3 glucan results in a selective susceptibility to superficial fungal infections (chronic fungal nail infections +/- mucosal Candida infections)
- Dectin-1 deficiency
- Caspase recruitment domain-containing protein 9 (CARD9) mutation
why are people with Impaired IL-17 immunity more susceptible to fungi infections
deficiency in IL_17 receptor - selective susceptibility to chronic superficial Candida infections in childhood
Vulnerable to superficial yeasts
describe how people with an Impaired number or function of neutrophils are susceptiblw to fungi infectinons
Lack of functional neutrophils predisposes to deep fungal infections, especially opportunist filamentous moulds.
NADPH oxidase system normally generates superoxide needed to kill fungi following phagocytosis in neutrophils
what diseases can leda to reduced numbers of circulating neutrophils
Severely reduced numbers of circulating neutrophils (= neutropenia) occurs in diseases of the bone marrow (e.g. leukaemia) or following cytotoxic chemotherapy for cancer.
Impaired function of neutrophils occurs in certain inherited disorders such as Chronic Granulomatous Disease in which there is a mutation in one of the genes of the neutrophil NADPH oxidase system that normally generates superoxide needed to kill fungi following phagocytosis – affected individuals have deep infections caused by filamentous moulds, especially Aspergillus.
Impaired T cell/macrophage - fungi suceptibility
yeasts and dimorphic fungi
how do we diagnose fungal infections
anti fungal drugs
disease and infection
describe Commensal infections
low density infection on human moist surfaces (= mucosa) without causing disease
e.g. Candida albicans in throat, gut, vagina
are Filamentous moulds part of normal human flora
Filamentous moulds are not part of normal human flora
describe Superficial fungal infections of skin, hair, nails
whats this?
Tinea pedis - Superficial infection of the foot
whats tis?
Tinea corporis - circular scaly superficial fungal infection of the body
whats this?
Tinea unguium - chronic fungal infection of the nails
describe subcutaneous fungal infections
Low virulence saprotroph fungi in soil or vegetation Mainly warm climates
Acquired by traumatic implantation through the skin Typically involves hands or feet
Farmers, gardeners, vets
The infection usually develops slowly
May remain localized or spread through lymphatics
Diagnosis by tissue biopsy and in vitro culture
e.g. dimorphic Sporothrix schenckii – filamentous mould on roses that invades as a yeast at 37oC
known as rose pickers disease
dimorphic Sporothrix schenckii
fat
mamba
