Week 9 Review

Question 1

What is the proper term for “viruses?”

Answer 1

viri

Question 2

Which scientists contributed to the history of viruses? How did these scientists contribute to the history of viruses?

Answer 2

Martinus Beijerinck: “father of virology”
Wendell Stanley: isolated viruses
- The infectious agent passes through the 0.2um filter

Question 3

What was the original and the current definition of viruses?

Answer 3

Acellular

Obligate intracellular parasite

Question 4

What components make up a virus?

Answer 4

Capsid + nuclei acid (DNA or RNA, ss or ds)

Question 5

Are viruses alive?

Answer 5

No b/c it’s acellular (cell theory = all living things are made of cells)

Question 6

What are other acellular agents? Give examples

Answer 6

Prion
- Protein folded abnormally, encephalitis
- Ex: scrapie, BSE

Viroid:
- Smallest nucleic acid-based pathogens
- Ex: plants

Question 7

What is the typical virus size and genome? What is the largest/smallest?

Answer 7

Virus: 20nm (microviridae) to 1000 nm (Filovirus)
Genome: 5000 bases (microviridae) to 1,000,000 (pandoravirus)

Question 8

What is the host specificity of a virus? Give examples.

Answer 8

Most viruses have a single species of host cells(infects specific species)
- M13 phage infects E.coli F pilus
- HIV attaches to CD4 (T cell)

Question 9

What is the capsid structure of a virus?

Answer 9

Virion: complete virus
- Nucleic acid inside protein capsid
- envelope/non-enveloped capsid cover: made from host plasma membrane, structurally not functionally similar to humans
- May have spokes

Question 10

What are the different types of morphology?

Answer 10

Helical: helical-shaped capsid, inside is nucleic acid (Tobacco mosaic virus)

Polyhedral: Pentagone shaped (Icosahedral, Human rhinovirus HRV14)

Complex: don’t fit into helical or polyhedral (bacteriophage)

Question 11

How are viruses classified? How do they differ?

Answer 11

International Union of Microbiological Societies Virology Division

Host specificity

Nature of genome (RNA, DNA, ss, ds, size)

Organization of capsid

Question 12

How are viruses named?

Answer 12

Family: -viridae
Genus: suffix-virus, common name

Ex:
Family Herpesviridae
Genus Simplexvirus
Human herpesvirus 2 (HHV-2)

Question 13

What are some examples of families of viruses that affect humans?

Answer 13

Coronaviridea
Papovaviridae
Herpesviridae
Picornaviridae

Question 14

How many families are there?

Answer 14

71 families, about 20 Animal family/genera medically significance

Question 15

What is the general life cycle of a virus? A prophage? An animal virus?

Answer 15

Stages: Bacterial and animal host

Attachment
Entry
Biosynthesis
Maturation
Release

Question 16

Give an example and describe the lytic cycle and the lysogenic cycles?

Answer 16

Virus replication: lysis and lysogeny
Lytic cycle:
Attachment: Phage attaches to surface of host
Penetration: Viral DNA enters host cell
Biosynthesis: Phage DNA replicates and phage proteins made
Maturation: New phage particles are assembled
Lysis: Cell lyses, releasing newly made phage

Lysogenic cycle:
Phage attach to host cell and injects DNA
Phage DNA circulates and enters lytic cycle or lysogenic cycle
Phage DNA integrates within the bacterial chromosome by recombination, becoming a prophage
Lysogenic bacterium reproduces normally
Occasionally, the prophage may excise from the bacterial chromosome by another recombination event, initiating a lytic cycle

Question 17

What are the results of lysogeny?

Answer 17

Lysogeny maintained by repressors-prevent lytic cycle gene expression

Lysogenic cell stops infection by same type phage

Phage conversion toxins associated w/infectious disease coded by prophages S. pyogenes->scarlet fever, botulinum botulism->botulism)

Specialized transduction

Question 18

What are the stages of specialized transduction?

Answer 18

Attachment and Penetration

Integration

Excision: Phage DNA excised along with piece of bacterial chromosome (Both DNA packed into new phage)

Infection: Phage with DNa (phage + piece of previous host) infects new host

Recombination: DNA from phage and previous host integrates into chromosome

Question 19

Compare and contrast the life cycle of bacteriophage and animal viruses.

Answer 19

Animal virus replication
Attachment: plasma membrane
- Receptor sites are inherited but can vary between individuals
Entry: receptor-mediated endocytosis/fusion
Uncoating of capsid
Biosynthesis (DNA vs RNA)
Release (budding: enveloped, rupture: nonenveloped)
- Attachment
- Penetration via endocytosis
- Uncoating
- Biosynthesis (viral DNA enters the nucleus)
- Assembly
- Release

In animal virus replication, the entire virus enters the cell, so an extra step to uncoat the capsid
In bacterial replication, phage remained outside of the cell

Question 20

Review RNA virus. Examples of RNA viruses?

Answer 20

Multiply in host cell cytoplasm
mRNA and viral
Include retroviridae (ex: HIV)
Uses enzyme reverse transcriptase

Question 21

Retrovirus Replication steps?

Answer 21

HIV fuses to the host-cell surface

HIV RNA, reverse transcriptase, integrase, and other viral proteins enter the host cell

Viral DNA is formed by reverse transcription

Viral DNA is transported across the nucleus and integrates into the host DNA

New viral RNA is used as genomic RNA and to make viral proteins

New viral RNA and proteins move to the cell surface and a new, immature HIV forms

The virus matures when protease releases proteins that form the mature HIV

Question 22

What is a latent infection? Give examples.

Answer 22

Viral genome persists w/o active production of virions
Prevents host defense from detecting virus
Triggers include physiological changes

Examples:
Includes Herpesviruses
- Herpes Simplex Viruses I and II (HSV 1, -2)
- EBV
- Cytomegalovirus (CMV)
HIV
HTLV1
Rabies virus

Question 23

What is the association between viruses and cancers?

Answer 23

Transformation= normal cell -> cancer cell
Metastasis: cancer cells spread from tissues where they arose
Oncogene: cancer-causing genes (transformation linked)
Oncogenic viruses or oncorviruses: induce tumors

• Small number of cancers caused by viruses
• Viral infection is 2nd leading of known cancers
• Common feature: integration of viral genome into host chromosome
• Cell cultures typically lose contact inhibition (surrounded by other cells to stop growth)

Question 24

Describe examples of DNA and RNA oncogenic viruses.

Answer 24

RNA:
Human T cell lymphotropic virus (HTLV 1, HTLV 2)
- Same family as HIV
- Associated w/ leukemias and lymphomas

DNA:
Human Papilloma Virus (HPV)
- Papovavirus family
- Common sexually transmitted infection
- Strong association with cervical cancer

Epstein-Barr (EB) virus
- Herpesvirus
- Targets lymphocytes
- Infects 80% of population
- Cause infectious mononucleosis in youth
- Linked to Burkitt’s lymphoma, possibly Hodgkin’s disease

Question 25

How were/are bacteriophage and animal viruses cultured?

Answer 25

Phage:
Plaque method
- Phage + bacteria
- Plaques: clearing

Animal:
Embryonated eggs used in past
Now: cell cultures
- Cell lines

Question 26

What is a cell line?

Answer 26

Animal cells growing on a Petri plate

Question 27

Why are fungi, algae, and helminths studied in microbiology?

Answer 27

Microscopic fungi include molds and yeasts. Helminths are multicellular parasitic worms. They are included in microbiology because their eggs and larvae are often microscopic.

Question 28

How are micro-eukaryotes classified? Give characteristics of each.

Answer 28

Fungi:
Kingdom: Fungi
Nutritional type: Heterotroph
Multicellular? All, except yeasts
Cellular arrangement: Unicellular, filamentous, fleshy
Food acquisition method: Absorptive
Characteristic features: sexual and asexual spores

Algae:
Kingdom: Protista
Nutritional type: Photoautotrophs
Multiceullarity: some
Cellular arrangement: unicellular, colonial, filamentous, tissues
Food acquisition method: diffusion
Characteristic features: pigments

Protozoa:
Kingdom: Various
Nutritional type: heterotroph
Multiceullarity: none
Cellular arrangement: unicellular
Food acquisition method: absorptive; ingestive
Characteristic features: motility; some form cysts

Helminths:
Kingdom: Animalia
Nutritional type: heterotroph
Multiceullarity: all
Cellular arrangement: tissues and organs
Food acquisition method: ingestive; absorptive
Characteristic features: elaborate life cycle

Question 29

How do molds grow? Yeast?

Answer 29

Molds:
- Start with spore, elongates, then forms germ tube
- Germ tube divides and forms hypha, eventually forming a mass of hyphae that forms filaments, called mycelium/thalus

Yeast: unicellular/filamentous
- Fission yeast: divides evenly (Schizosccharomyces sp.)
- Budding yeast: divide unevenly (Saccharomyces sp.)
- Dimorphic (either mold or yeast (37C yeast, 25C mold)

Question 30

What is the asexual and sexual life cycle of fungi?

Answer 30

Asexual: offspring genetically identical
- Fragment hyphae
- Spore (unit that grows into an adult)

Sexual: Two parents contribute to genetic information, and offspring are unique
- Plasmogamy: nucleus of donor cell (+) penetrates cytoplasm of recipient cell (-)
- Karyogamy: the (+) and (-) nuclei fuse
- Meiosis: daughter cells half # chromosomes

Question 31

What are the medically significant fungi? What are the sexual and sexual spores for each?

Answer 31

Zygomycota (Conjugation fungi):
Asexual: sporangiospores (sac)
Sexual: Zygospores

Ascomyocta (Sac fungi):
Conidiospore (not in sac)
Ascospores

Basidiomycota (Club fungi):
Conidiospore (not in sac)
Basidiospores

Question 32

Describe the generalized life cycle of basidiomycete.

Answer 32

Hyphal fragment breaks off vegetative mycelium

Fragment grows to produce new mycelium

Vegetative mycelium grows

Plasmogamy

The fruiting structure (mushroom) develops

Basidiospores are formed by meiosis

Basidiospores mature

Basidiospores discharged

Basdiopsore germinates. Produce hyphae

Question 33

What are common microalgae? Why are they important?

Answer 33

Green and red algae: photosynthesis

Diatoms (fossils make diatomaceous earth(used filtration, insulation)

Dinoflagellates: The most important component of plankton, Red tide (harmful algal bloom)

Question 34

What is the typical life cycle, locomotion, and common examples of protozoans?

Answer 34

The general life cycle of most protozoans has two phases. The first phase is the proliferative stage which involves the formation of the trophozoites. These trophozoites are in a fast-working and active feeding state. The second phase is the resting cyst phase.

Three major types of locomotion:
- Pseudopodia
- Cilia
- Flagella

Common protozoans:
Archaezoa: diverged before origin mitochondria
Rhizopoda: amoebas, slime molds
Apicomplexa: parasitic, plasmodium (malaria)

Question 35

What are the most common medically significant helminths, including structures and life cycles?

Answer 35

Nematoma (roundworms) >15000 species
- Pinworms: most common infection in the U.S, female lays eggs around anus -> itching
- Hookworm: intestinal, main transmission = walking barefoot on soil, mainly tropical climates w/ poor hygiene
- Trichinellosis: from undercooked meat, larvae encyst in muscles
- Heartworm in animals: transmitted by mosquitos

Platyhelminths (flatworms)
- Flukes (trematodes): oral suckers, complex life cycles, multiple hosts, schistosomiasis (2nd in scale of parasitic disease to malaria)
- Tapeworms (cestodes): may have oral suckers or hooks, infections from undercooked meat

Life Cycle of Tapworm:
- Eggs or gravid proglottids in feces are passed into the environment
- Cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated by eggs or gravid proglottis
- Oncospheres hatch, penetrate the intestinal wall, and circulate to musculature
- Humans are infected by digesting raw or uncooked infected meat
- Scolex attaches to the intestine
- Adults in small intestine