Module 3 - Viruses and Fungi Flashcards
What is the fundamental structure of every virus?
A nucleic acid (DNA/RNA) surrounded by a capsid
What is different between a virus’ extracellular and intracellular states?
Extracellular: metabolically inert; stable structure which protects genome
Intracellular: stable protective capsid breaks down; redirects host machinery - reliant on host cell metabolism
What are the two kinds of symmetry viruses can show?
Helical symmetry, and isocahedral (5-3-2) symmetry
Name the 6 stages of the virus replication cycle
Attachment, Penetration, Uncoating, Synthesis, Assembly, Release
Name the process(es) by which viruses generally and leave a host cell?
Enter by endocytosis, Exit by budding
What happens during the uncoating phase of a virus life cycle?
The protective capsule breaks down so that the viral genome can be released into the cell
How do viruses leave an animal cell?
Enveloped viruses generally leave via exocytosis, taking a part of the cell membrane with them; naked viruses often simply lyse the cell and are released
What type of nutrition do fungi show?
They are organoheterotrophs - they break down polymers outside of the cell using hydrolytic enzymes)
Name the 5 major phyla of kingdom fungi
Basidiomycota, Ascomycota, Glomeromycota, Zygomycota, Chytridiomycota
Describe the structure of chytridiomycota
Aquatic fungi with flagellated, motile, asexual and sexual spores; have a single large thallus containing motile zoospores, and from which rhizoids emerge
Describe the structure of zygomycota
Terrestrial fungi with non-motile, asexual spores (found in sporangium); have a large sexual zygospore
Describe the structure of ascomycota
Produces aerial-borne chains of asexual conidiospores; 8 sexual ascospores are contained in a single ascus -> asci borne on ascocarp
Describe the structure of basidiomycota
Form mushrooms and toadstools; usually form 4 sexual basidiospores on a club-like structure called the basidium; the basidia line the gills or pores of the mushroom
What determines whether Dimorphic fungi are in a yeast or filamentous form?
Temperature: (e.g., for some, 37C = yeast, 20-25C = filamentous)
Describe how unicellular fungi grow
Budding - a form of asexual reproduction. (A new organism grows from a bud/outgrowth on a parent cell, remaining attached as it grows, and only separating once it is mature)
Describe how filamentous fungi spread
From a mat of hyphae, aerial hyphae grow up, and form sexual spores called conidia
Name the two types of Hyphae structure in terms of separate cells
Septate (cells separated by septa) or coenocytic (single, multinucleated cell)
Describe the structure of chitin
Polymer of N-acetylglucosamine; forms microfibrillar bundles
Which fungal hypha is most primitive and why?
Chytridiomycota - they are the only phylum to still possess a flagella
What type of growth occurs in hyphae, and what advantage does this provide?
Apical growth - gives penetrating power
What processes/forces power growth of hyphae?
Actin polymerisation; cytoplasmic expansion forces
What is the Spitzenkorper?
A cluster of micro-vesicles (chitosomes) and macrovesicles, embedded in a meshwork of actin filaments
What do the vesicles in the Spitzenkorper contain?
- Enzymes involved in cell wall biosynthesis
- Enzyme activators GTP and Protease
- Enzymes involved in cell wall lysis
- Pre-formed wall polymers e.g., Mannoproteins
What 3 things do NOT apply to viruses? (Sorry weirdly phrased question)
They are NOT alive, canNOT generate ATP and do NOT have ribosomes
What IS a virus?
A small, infectious, obligate intracellular parasite
What is the usual size range of viruses?
20 nm to 1.5 µm
Which are the only group of viruses that are big enough to be seen without an electron microscope?
Those that infect Amoebozoa
Ultrastructure of Tobacco Mosaic Virus?
Helical, +ssRNA genome, naked (i.e. no envelope)
Ultrastructure of Adenoviruses?
Icosahedral, DNA genome, glycoproteins on surface of capsid
What are the two types of viruses that can have both DNA and RNA genomes depending on the stage of the replication cycle?
Retroviruses (e.g., HIV) and Hepadnaviruses (e.g., HepB)
How do retroviruses replicate?
They have an RNA genome but replicate via a DNA intermediate, then use reverse transcriptase to translate their RNA into DNA in the host cell
How do hepadnaviruses replicate?
DNA genome which replicates via an RNA intermediate
What are viral capsids?
A protein coat or shell made up of capsomere units - can be a polymer of a single protein (e.g., in parvovirus) or several proteins (e.g., adenovirus, smallpox)
Name 3 ENVELOPED viruses (i.e. surrounded by a membrane as well as capsid)
Influenza, Coronavirus, Herpes
What happens during the latent period on a viral one-step growth curve?
Adsorption, Eclipse and Maturation
(Synthesis of early enzymes, nucleic acids and protein coats must take place)
How long does the whole process from Adsorption to Release take for bacteriophages and for animal viruses?
30-60 minutes for phages, 8-40 hours for animal viruses
What are the three (general) distinct regions of growing hyphae?
Apical region, Subapical region and Vacuolation Zone
Name the layers of the fungal cell wall
(Moving outward from cell membrane) Chitin; ß1-3 and ß1-6-glucan; Mannoproteins
