Module 3 - Viruses and Fungi

Question 1

What is the fundamental structure of every virus?

Answer 1

A nucleic acid (DNA/RNA) surrounded by a capsid

Question 2

What is different between a virus’ extracellular and intracellular states?

Answer 2

Extracellular: metabolically inert; stable structure which protects genome
Intracellular: stable protective capsid breaks down; redirects host machinery - reliant on host cell metabolism

Question 3

What are the two kinds of symmetry viruses can show?

Answer 3

Helical symmetry, and isocahedral (5-3-2) symmetry

Question 4

Name the 6 stages of the virus replication cycle

Answer 4

Attachment, Penetration, Uncoating, Synthesis, Assembly, Release

Question 5

Name the process(es) by which viruses generally and leave a host cell?

Answer 5

Enter by endocytosis, Exit by budding

Question 6

What happens during the uncoating phase of a virus life cycle?

Answer 6

The protective capsule breaks down so that the viral genome can be released into the cell

Question 7

How do viruses leave an animal cell?

Answer 7

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

Question 8

What type of nutrition do fungi show?

Answer 8

They are organoheterotrophs - they break down polymers outside of the cell using hydrolytic enzymes)

Question 9

Name the 5 major phyla of kingdom fungi

Answer 9

Basidiomycota, Ascomycota, Glomeromycota, Zygomycota, Chytridiomycota

Question 10

Describe the structure of chytridiomycota

Answer 10

Aquatic fungi with flagellated, motile, asexual and sexual spores; have a single large thallus containing motile zoospores, and from which rhizoids emerge

Question 11

Describe the structure of zygomycota

Answer 11

Terrestrial fungi with non-motile, asexual spores (found in sporangium); have a large sexual zygospore

Question 12

Describe the structure of ascomycota

Answer 12

Produces aerial-borne chains of asexual conidiospores; 8 sexual ascospores are contained in a single ascus -> asci borne on ascocarp

Question 13

Describe the structure of basidiomycota

Answer 13

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

Question 14

What determines whether Dimorphic fungi are in a yeast or filamentous form?

Answer 14

Temperature: (e.g., for some, 37C = yeast, 20-25C = filamentous)

Question 15

Describe how unicellular fungi grow

Answer 15

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)

Question 16

Describe how filamentous fungi spread

Answer 16

From a mat of hyphae, aerial hyphae grow up, and form sexual spores called conidia

Question 17

Name the two types of Hyphae structure in terms of separate cells

Answer 17

Septate (cells separated by septa) or coenocytic (single, multinucleated cell)

Question 18

Describe the structure of chitin

Answer 18

Polymer of N-acetylglucosamine; forms microfibrillar bundles

Question 19

Which fungal hypha is most primitive and why?

Answer 19

Chytridiomycota - they are the only phylum to still possess a flagella

Question 20

What type of growth occurs in hyphae, and what advantage does this provide?

Answer 20

Apical growth - gives penetrating power

Question 21

What processes/forces power growth of hyphae?

Answer 21

Actin polymerisation; cytoplasmic expansion forces

Question 22

What is the Spitzenkorper?

Answer 22

A cluster of micro-vesicles (chitosomes) and macrovesicles, embedded in a meshwork of actin filaments

Question 23

What do the vesicles in the Spitzenkorper contain?

Answer 23

• Enzymes involved in cell wall biosynthesis
• Enzyme activators GTP and Protease
• Enzymes involved in cell wall lysis
• Pre-formed wall polymers e.g., Mannoproteins

Question 24

What 3 things do NOT apply to viruses? (Sorry weirdly phrased question)

Answer 24

They are NOT alive, canNOT generate ATP and do NOT have ribosomes

Question 25

What IS a virus?

Answer 25

A small, infectious, obligate intracellular parasite

Question 26

What is the usual size range of viruses?

Answer 26

20 nm to 1.5 µm

Question 27

Which are the only group of viruses that are big enough to be seen without an electron microscope?

Answer 27

Those that infect Amoebozoa

Question 28

Ultrastructure of Tobacco Mosaic Virus?

Answer 28

Helical, +ssRNA genome, naked (i.e. no envelope)

Question 29

Ultrastructure of Adenoviruses?

Answer 29

Icosahedral, DNA genome, glycoproteins on surface of capsid

Question 30

What are the two types of viruses that can have both DNA and RNA genomes depending on the stage of the replication cycle?

Answer 30

Retroviruses (e.g., HIV) and Hepadnaviruses (e.g., HepB)

Question 31

How do retroviruses replicate?

Answer 31

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

Question 32

How do hepadnaviruses replicate?

Answer 32

DNA genome which replicates via an RNA intermediate

Question 33

What are viral capsids?

Answer 33

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)

Question 34

Name 3 ENVELOPED viruses (i.e. surrounded by a membrane as well as capsid)

Answer 34

Influenza, Coronavirus, Herpes

Question 35

What happens during the latent period on a viral one-step growth curve?

Answer 35

Adsorption, Eclipse and Maturation
(Synthesis of early enzymes, nucleic acids and protein coats must take place)

Question 36

How long does the whole process from Adsorption to Release take for bacteriophages and for animal viruses?

Answer 36

30-60 minutes for phages, 8-40 hours for animal viruses

Question 37

What are the three (general) distinct regions of growing hyphae?

Answer 37

Apical region, Subapical region and Vacuolation Zone

Question 38

Name the layers of the fungal cell wall

Answer 38

(Moving outward from cell membrane) Chitin; ß1-3 and ß1-6-glucan; Mannoproteins