AuCoin I: Viral Classification

Question 1

Viruses are (blank) agents.

Answer 1

filterable

**can pass through a filter

Question 2

Viruses are obligate intracellular parasites. What does this mean?

Answer 2

viruses can’t make energy or proteins independently of a host cell

Question 3

Are viral genomes DNA or RNA?

Answer 3

may be either, but not both

Question 4

Viruses have a (blank) or an envelope morphology

Answer 4

naked capsid

Question 5

Are viruses living? What must they do to endure in nature? How do viruses infect humans and other hosts?

Answer 5

no; they must be infectious; mutation and selection

Question 6

Viruses can enter a cell, but they must be able to use (blank) to produce their components. Viruses must encode any required processes not provided by the cell.

Answer 6

host cell processes

ex: use transcription factors from the host cell

Question 7

Components of a virion? What can happen to naked capsids?

Answer 7

DNA or RNA
structural proteins
enzymes + nucleic acid binding proteins

these form a nucleocapsid or a naked capsid

nucleocapsids may gain glycoproteins and a membrane and become an ENVELOPED virus

Question 8

What are some examples of naked capsid viruses or unenveloped viruses?

Answer 8

papilloma virus
adenovirus
poliovirus

Question 9

What are some examples of enveloped viruses?

Answer 9

herpesvirus

retroviruses

Question 10

What are some means of classifying viruses?

Answer 10

structure - size, morphology, nucleic acid
biochemical characteristics - structure/mode of replication
disease - what do they cause
means of transmission - arbovirus = spread by insect
tissue or organ

Question 11

What is an arbovirus?

Answer 11

virus spread by insects

Question 12

What is a RETROvirus?

Answer 12

synthesized DNA from RNA

Question 13

Are there more DNA viruses or RNA viruses?

Answer 13

RNA viruses

Question 14

Can + sense RNA cause infection? Can - sense?

Answer 14

yes - it is like messenger RNA and will infect a host cell; negative sense will not infect a host cell

Question 15

Viruses are measured in (blank)

Answer 15

nanometers

Question 16

What is the largest virus that can be seen under a light microscope?

Answer 16

poxviruses

Question 17

Why are some viruses large vs small?

Answer 17

larger viruses hold larger genomes and are more complex

Question 18

Describe the structure of a virion. What can be found between the capsid and the envelope?

Answer 18

virion = nucleic acid genome packaged into a protein coat (capsid) or within a larger membrane (envelope); in between the capsid and the envelope, you may find a tegument layer packed with viral proteins

Question 19

Target cells for viruses have receptor proteins. How do viruses bind to their target?

Answer 19

viral attachment proteins are located on the surface of the capsid or envelope - these mediate the interaction of the virus and target cell

Question 20

Antibodies that bind viral attachment proteins on the virus and block infection are (blank) antibodies

Answer 20

neutralizing

Question 21

The capsid is a rigid structure. This makes viruses with naked capsids resitant to (blank)

Answer 21

drying, acid, and detergents

Question 22

How can naked capsid viruses be transmitted?

Answer 22

fecal oral route or in sewage

Question 23

What does the viral envelope contain?

Answer 23

lipids, proteins, and glycoproteins

Question 24

Viral envelops are maintained only in aqueous solutions. So, how are they transmitted?

Answer 24

in body fluids

Question 25

Capsids can be (blank): self assemble on the RNA gemone and form a (blank)

Answer 25

helical (rod); ribonucleocapsid

Question 26

Helical capsids are found within what type of viruses?

Answer 26

found within most negative-strand RNA viruses

Question 27

Capsids can be (blank), which take the form of a sphere that is assembled from symmetrical subunits. Simple icosahedrons like picornaviruses are made of 12 (blank) each with fivefold symmetry (pentamer)

Answer 27

icosahedrons; capsomers

Question 28

What are viral envelopes composed of?

Answer 28

lipids, proteins, glycoproteins - formed from cellular membranes

Question 29

Most (blank) on viruses act as VAPs that bind to target cells to initiate entry. VAPs that bind to red blood cells are (blank)

Answer 29

glycoproteins; hemagglutinins

Question 30

The glycoproteins on the viral envelop can form (blank) that are usually immunodominant.

Answer 30

spikes **these cause an immune response

Question 31

All of the negative strand RNA viruses have this

Answer 31

an envelope

Question 32

(blank) is situated between the envelope and nucleocapsid - contains enzymes, and other proteins that facilitate viral infection. (Herpesviruses)

Answer 32

tegument layer

Question 33

Does the host cell assist the virus in replication?

Answer 33

yes; the host cell provides substrates, energy, and some of the machinery necessary for viral replication

Question 34

What are the phases of viral replication?

Answer 34

1. virus recognizes its target cell via VAPs 2. it attaches and penetrates the plasma membrane 3. it uncoats its genome into the cytoplasm and delivers the genome to the nucleus 4. viral genome replicates and transcription occurs to produce necessary proteins 5. virus assembles and is released via lysis or like the secretory pathway in vesicles?

Question 35

Which cells a virus infects are dependent on its VAPs. VAPs are usually specific (blank) of enveloped viruses. Viruses may bind to receptors on cell types of (blank) only

Answer 35

glycoproteins; specific species

Question 36

The cell that is susceptible to viral binding defines the tissue (blank)

Answer 36

tropisms

Question 37

The HA of influenza A virus binds to (blank) expressed on many different cells and has a (blank) host range and tissue tropism

Answer 37

sialic acid receptors; broad

Question 38

How do most nonenveloped viruses enter the host cell?

Answer 38

receptor mediated endocytosis

Question 39

How do enveloped viruses deliver the nucleocapsid or genome into the cytoplasm of the host cell?

Answer 39

by fusing its membrane

Question 40

T/F: Fusion proteins may be active at neutral pH or may need acidic conditions of an endosome to fuse

Answer 40

true

Question 41

Where are most DNA genomes delivered in the host cell? What about RNA genomes?

Answer 41

to the nucleus; RNA genomes remain in the cytoplasm

Question 42

Most DNA viruses use the cells (blank) and other enzymes to make mRNA; mRNA must acquire what two components?

Answer 42

DNA-dependent hose RNA polymerase II; 3' poly A tail and 5' methylated cap

Question 43

Most RNA viruses replicate and produce (blank) in the cytoplasm. Therefore, the virus must encode the (blank) for transcription

Answer 43

mRNA; enzymes

Question 44

What types of viruses replicate in the nucleus?

Answer 44

DNA viruses - retroviruses and influenza

Question 45

Some complex DNA viruses encode their own (blank) to regulate the expression of viral genes. Viral DNA replication begins at the (blank). Viral replication factors bind to this region.

Answer 45

trx factors; origin

Question 46

Viruses with large DNA can encode their own (blank) which makes room for errors and mutations - these polymerases can be the target of (blank)

Answer 46

DNA polymerase; antiviral nucleotide analogs

Question 47

Describe the process of DNA viral replication

Answer 47

1. attachment and penetration of host cell via fusion 2. moves to the nucleus 3. immediate early protein synthesis -- trx factors 4. early protein synthesis and genome replication 5. late protein synthesis 6. DNA containing naked capsids enter ER, gain mature glycoproteins and become mature enveloped virions 7. exocytosis and release of mature virions

Question 48

RNA virus must encode a (blank). These polymerases are fast and have a high (blank)

Answer 48

RNA-dependent RNA polymerase; mutation rate

Question 49

The (blank) RNA viral genomes act as mRNA, bind to ribosomes, and direct protein synthesis Therefore, this (blank) viral RNA alone can initiate infection RNA-dependent RNA polymerase will produce a (blank) RNA template that can be used to produce more (blank) RNA

Answer 49

+ strand; + strand; - strand; + strand

Question 50

What is the template for production of + mRNA?

Answer 50

- strand mRNA **NOT INFECTIOUS

Question 51

Where does RNA viral transcription and replication occur?

Answer 51

in the cytoplasm, except for influenza viruses

Question 52

What does the 5' cap structure of viral mRNA do?

Answer 52

mediates binding of viral mRNA to host ribosomes

Question 53

(blank) bind to viral mRNA and may produce one large polyprotein which needs to be cleaved by cellular or viral proteases Viral mRNA is preferentially translated in many cases. Some viruses block cellular mRNA egress from the (blank) Some viral proteins require post-translational modifications such as (blank) Viral glycoproteins are synthesized on membrane-bound (blank) and have the amino acid sequences to allow for (i) insertion into the rough endoplasmic reticulum and (ii) N-linked glycosylation

Answer 53

ribosomes; nucleus; phosphorylation and glycosylation; ribosomes

Question 54

When the concentration of viral structural components is high enough in the cell then protein-protein, protein-nucleic acid, and protein –membrane interactions occur Viral (blank) occurs after association of the nucleocapsid with the intracellular portion of viral glycoproteins Most RNA viruses bud from the (blank) Other viruses acquire their envelope by budding into the (blank)

Answer 54

budding; plasma membrane; Er and golgi

Question 55

What are some ways viruses can be released?

Answer 55

cell lysis exocytosis budding from the plasma membrane

Question 56

What is the difference in lethal mutations vs attenuated mutations?

Answer 56

attenuated mutations cause less severe disease

Question 57

In what ways can viruses undergo mutation?

Answer 57

new strains are produced by recombination or segmented genomes can shuffle their segments

Question 58

Can the + strand viral RNA alone initiate infection? Can the - strand viral RNA initiate infection?

Answer 58

yes; no, not unless the polymerase is present

Question 59

What provides the template to produce more + strand RNA?

Answer 59

- strand RNA