Viruses

Question 1

How do viruses differ from life forms? (4)

Answer 1

-no functional organelles
-cannot produce their own energy/macromolecules
-metabolically inert outside of the host cell
-do NOT multiply by binary fission (can only replicate/survive within a host cell)

Question 2

Obligate Intracellular Parasites

Answer 2

Ie. Viruses —> can only replicate/survive within a host cell

Question 3

Are viruses alive? How do we know?

Answer 3

Yes: they can replicate within a cell, can be inactivated/denatured, and possess + replicate genes/simple genomes
- however, they require host symbiosis (are obligate parasites)

Question 4

Death of cell is called

Answer 4

Lysis

Question 5

Replication of the virus within a host cell results in:

Answer 5

Lysis (death of cell) which results in disease

Question 6

What are the structural components of viruses?

Answer 6

-Nucleic Acid (RNA or DNA - not both)
-Surrounded by the Capsid (protein coat)
Some viruses may also contain:
-Lipid Envelope that contains Membrane Glycoprotein (recognition of host cell)

Question 7

How big are viruses?

Answer 7

20-300nm (ie. VERY small
- requires an electron microscope to see)

Question 8

Three types of “Giant Viruses” that have been discovered in amoeba:

Answer 8

• Mimivirus
• Pandoravirus
• Pithovirus

Question 9

What structural component gives a virus its shape?

Answer 9

The Capsid

Question 10

How many virus shapes are there?

Answer 10

Three

Question 11

What are the three types of Virus shape? Describe them and give an example.

Answer 11

1. Helical: capsid is cylindrical or “rod shaped”. May or may not have an envelope ex. Rhabdo Viruses (rabies) or Filoviruses (Ebola)
2. Icosohedral: capsid is dimensional and somewhat round. May have an envelope ex. Retrovirus (feline leukemia) or NO envelope ex. Parvovirus
3. Complex: capsid is a more complex arrangement, can be a combination of helical or icosohedral ex. Pox virus and bacteriophages

Question 12

Virus nucleic acid contains either _____ or _____ and can be further classified as _____ or _____

Answer 12

DNA; RNA Linear; Circular

Question 13

DNA / RNA in viruses can be _____ or _____ stranded

Answer 13

Single or double stranded

Question 14

Example of DNA Linear Single Strand Virus

Answer 14

Parvovirus

Question 15

Example of DNA Linear Double Stranded Virus

Answer 15

Herpesvirus

Question 16

Example of DNA Circular Single Stranded Virus

Answer 16

M13

Question 17

Example of DNA Circular Double Stranded Virus

Answer 17

Baculovirus

Question 18

Example of RNA Linear Single Stranded Virus

Answer 18

TMV

Question 19

Example of RNA Linear Double Stranded Virus

Answer 19

Reovirus

Question 20

Example of RNA Circular Single Stranded Virus

Answer 20

Hepatitis D

Question 21

Example of RNA Circular Double Stranded Virus

Answer 21

Trick: does not exist

Question 22

Most viruses possess what type of genome

Answer 22

Single Stranded RNA

Question 23

How do viruses recognise host cells?

Answer 23

Surface cell receptors

Question 24

How do viruses infect their host (simplest terms)

Answer 24

Virus recognizes host cell through surface cell receptors; virus enters cell, sheds shell, and releases protein; virus takes cell’s energy (cell is often destroyed and bursts); virus moves on to a new cell

Question 25

Viruses are classified into groups based on what criterion?

Answer 25

-type of nucleic acid (DNA or RNA?) -shape of capsid (helical or icosahedral or complex?) -envelope present or not? -replication strategy -genome sequence and organization -other criteria (size, pH sensitivity, host range)

Question 26

Virus species name is often just

Answer 26

The name of the disease. Example: Rabies Virus causes Rabies

Question 27

How is the taxonomical naming of viruses different from other organisms

Answer 27

Viruses show only the species name, not the genus name

Question 28

Viruses can be named after the place where they were first isolated. Give two examples.

Answer 28

-Hendra Virus -Newcastle Disease Virus

Question 29

Similar to other organisms, viruses are classified into:

Answer 29

-Family -Genus -Species

Question 30

What are three virus evolution theories? What are some problems associated with each theory?

Answer 30

1. Viruses are escaped pieces of host cell DNA (ie. escaped cell and evolved as its own entity) -Does not work for full virus genomes (ie. viruses with more than one gene) 2. Viruses are degenerate unicellular life forms (ie. viruses were once cells but overtime lost certain genes that weren’t needed) -Does not work as the viral genome sequence does not resemble the genome sequence of unicellular life 3. Viruses originated independently from host replication systems, with several separate viral origins occurring at different times (ie. Viruses evolved alongside cells)

Question 31

Describe the best supported theory on how Viruses may have evolved

Answer 31

Viruses originated independently from complex molecules of protein and nucleic acid, evolving alongside their hosts. Several separate viral origins

Question 32

Why are viruses so difficult to track from an evolutionary standpoint?

Answer 32

-Viruses leave no geological fossils -Viruses have a huge range of diversity, indicating multiple ancestors

Question 33

How are Henipaviruses transmitted? What species are affected?

Answer 33

-Fruit bats (flying foxes) are a reservoir host of Henipaviruses -Transmitted to horses as Hendra Virus -Transmitted to pigs as Nipah Virus -ZOONOTIC

Question 34

Why are viruses labelled as “important infectious diseases”

Answer 34

-quickly occurring mutation leading to increased virulence and expanded host range -disrupts ecosystems