Module 3 - Viruses and Fungi Flashcards
Viruses: what are they, why do they not count as living, and what key features are there?
Small, infectious, obligate, intracellular parasites
They rely on host cells to reproduce for them and produce ATP as they cannot reproduce themselves and no known viruses contain mitochondria (or ribosomes either)
May contain RNA as the genome instead of DNA
Viral genomes
1) SS or DS DNA
2) SS or DS RNA
3) Use both DNA and RNA (retrovirus - uses reverse transcriptase to convert RNA into DNA(HIV)) (Hepadnavirus - uses an RNA intermediate to replicate its DNA)
Virion: structure
Always a nucleic acid surrounded by the capsid (protein coat/shell)
Capsid - polymer of a single/multiple proteins
Some viruses have membranes too
What happens when a virus enters a host cell?
Its stable capsid is released and the genome is released and the viral replication redirects the host machinery
Helical symmetry
Size - 18-300nm
Length determined by RNA length
Width determined by subunits
Icosahedral symmetry
20 faces - most efficient packing in a closed shell
Complex viruses
Bacteriophages - icosahedral head, helical tail sheath, tail fibres, infect bacteria only, carry lysozyme for cell entry (breaks peptidoglycan)
Virus replication cycle
Induces host cell to synthesise viral components
1 - Attachment
2 - Penetration
3 - Uncoating
4 - Synthesis of nucleic acid and protein
5 - Assembly of subunits and genome packaging
6 - Mature virion released
Viral growth curve: the steps
1- Adsorption into the cell
2 - Eclipse (nucleic acid/coat separated)
3 - Latent period (synthesis begins)
4 - Maturation (viruses matured)
5 - Assembly and release
Fungi: what are they, when did they arrive on land, and what are the other key features?
Organoheterotrophic (saprotrophs) eukaryotes with chitin as the cell wall that are mostly aerobic and haploid
430,000 million years ago
- 100,000 species are identified out of an estimated 1.5 million
- 70s mitochondria ribosomes
6 Major phyla of fungi
*Microsporidia (unicellular animal/protist parasites)
*Chytridiomycota (flagellated and motile spores)
*Zygomycota (Sexual/asexual phases - mould)
*Glomeromycota (Symbiotic with plants)
*Ascomycota (Cell division as budding)
*Basidiomycota (Classic mushroom)
Microsporidia
Parasitic fungi - only on eukaryotes/protists
Chytridiomycota: what are they, what key features do they have, and where are they found?
Most primitive aquatic fungi with flagellated asexual/sexual spores
Has a large thallus from which rhizoids emerge and contain motile zoospores
- Present in the rumen of cattle as an important part of the digestive process
- Causes fatal disease in amphibians
Zygomycota: what are they, what key features do they have, and where are they found?
Terrestrial asexual fungi with non-motile spores
Have a large sexual zygospore
Organic material that isn’t alive, for example, they’re a large part of causing food to spoil
Glomeromycota
Symbiosis with plants
Ascomycota: what are they, what key features do they have, and where are they found?
Fungi with large fruiting bodies that also produce aerial-borne chains of asexual conidiospores
The most diverse group (includes Penicillium and Aspergillus)
Found as plant pathogens/food spoilage
Basidiomycota: what are they, what key features do they have, and where are they found?
The club-shaped “mushrooms and toadstools” group with Basidia lining the gills/pores of the mushroom usually with four sexual basidiospores borne on a basidium
Most advanced group
Many form mycorrhizal associations with trees
The use of hyphae in fungi
Apical growth of hyphae enables fungi to extend into fresh zones of the substrate
Enzymes are released from hyphae and diffuse into the surrounding media.
Released nutrients and minerals form from the decomposition of organic matter for e.g. are taken up into the hyphae
What are the two types of hyphae and what does each do?
- Septate - fungal hyphae are divided into separate cells by perforated septa. Tiny holes in the septa allow the flow of nutrients between cells.
- Coenocytic - No septa, large cells with multiple nuclei.
Chitin: what is it?
Polymer of N-acetylglucosamine
Fungal hyphae growth: what is it, how does it occur, and what does the growth give the fungi?
Only occurs at the tip of hyphae in the apical region (can be rapid – up to 40mm/min)
There is continuous movement of materials into the tip from older regions of the hyphae also the growth is powered by actin polymerisation and cytoplasmic expansion forces
Apical growth gives penetrating power- enables penetration of plant cells, insect cuticles, and hard materials such as wood
Hyphal growth: what is the actual process?
- Secretory vesicles derived from the Golgi are transported to the top
- Vesicles fuse with the plasma membrane at the tip and release their contents: enzymes involved in cell wall biosynthesis; glucan synthase; chitin synthase.
- Enzyme activators GTP (glucan synthase) and protease (chitin synthase)
- Enzymes involved in cell wall lysis
- Preformed wall polymers such as mannoproteins
The three regions of hyphae
Apical region - bigger actin cytoskeleton, more actin microfilaments and microtubules, less cell wall crosslinking. ~50nm thick
Subapical region - less of an actin skeleton, with a rigified cell wall with more crosslinking
Vacuolation zone - higher cell wall cross-linking, smaller actin cytoskeleton, most organelles are here
