Ch. 13

Question 1

Why are viruses nonliving?

Answer 1

They cannot reproduce on their own

Question 2

What is defined as the number of different host cells that virus can infect
- limited to single bacterial species for a single phage or virus

Answer 2

Host range

Question 3

What 4 factors limit host range

Answer 3

1. attachment to host receptors
2. host attachment sites
3. bacteriophages
4. animal viruses

Question 4

T or F once one virus enters a host cell no other viruses can enter?

Answer 4

True

Question 5

What are the 3 general characteristics of viruses?

Answer 5

1. Non-living entities
2. infect organisms of every domain
3. referred to by organism they infect (Animal viruses, Plant viruses, Bacteriophage)

Question 6

Who first proposed the term virus?

Answer 6

Louis Pasteur

Question 7

1. what is a virion?
2. Virions can have DNA, RNA, or both?

Answer 7

1. complete, fully developed viral
   particle
2. Can have DNA or RNA, never both

Question 8

math the virion structure to its definition (envelope, nucleic acid, spikes, capsid):

1. DNA or RNA can be single- or
   double-stranded; linear or circular
2. protein coat made of capsomeres
   (subunits)
3. lipid, protein, and carbohydrate
   coating on some viruses.
   - Partially formed from the plasma membrane of the host cell when the virus buds from the cell
4. projections from outer surface
   - found on some enveloped viruses
   ▪ Made of carbohydrate and protein
   ▪ May be used for attachment

Answer 8

1. Nucleic acids
2. capsid
3. envelope
4. spikes

Question 9

What are the 2 phases in Obligate intracellular parasites? Which one is metabolically inert and active?

Answer 9

1. extracellular phases (inert)
2. Intracellular phase (active)

Question 10

Which is more resistant to killing, naked virus or envelope virus?

Answer 10

Envelope virus because they have a plasma membrane that is more susceptible.

Question 11

does multiplication take place inside or outside of the host cell during the replication cycle?

Viruses use host machinery to support __________

Answer 11

inside a host cell

reproduction

Question 12

T/F Viral genome is DNA and RNA

Answer 12

FALSE, it is either DNA OR RNA, never both

Question 13

complete complex of nucleic acid and protein packaged in the virion

Answer 13

Nucleocapsids

Question 14

Determine which type of virus this is based on the characteristics below:

• Have membrane surrounding nucleocapsid
• Lipid bilayer with embedded proteins
• Lipid bilayer with embedded proteins
• Common in Animal viruses
• Envelope makes initial contact with host cell

Answer 14

Enveloped Viruses

Question 15

T/F Complex viruses are virions composed of several parts with separate shapes and symmetries

Answer 15

TRUE

Question 16

In comparison to bacterial cells viruses are what?

Answer 16

very small in size

Question 17

What are the Two alternative mechanisms of multiplication of bacteriophages?

Answer 17

1. Lytic cycle
2. Lysogenic cycle

Question 18

1. which viral symmetry has spherical viruses? (e.g., human papillomavirus)

• Most efficient arrangement of subunits in a closed shell

Answer 18

1. Icosahedral viral symmetry

Question 19

________ __________: causes lysis and death of the host cell
_________ __________: Phage DNA is incorporated in the host DNA

Answer 19

1. Lytic cycle
2. lysogenic cycle

Question 20

1. which cycle (lytic or lysogenic) involves productive infection?
2. when there is a lysis of cells and release of virions what happens to the host cell?
3. when there is a release of virions and non-lysis of cells what happens to the host cell?

Answer 20

1. Lytic cycle
2. It dies
3. host cell burst (multiplies), continuous leakage of virions

Question 21

1. In which cycle (lytic or lysogenic) does the nucleic acid of virus become part of host cell DNA or replicates as a plasmid?
2. What is the state of the host cell being described above?
3. At the end of the lysogenic cycle what happens to the host cell?

Answer 21

1. Lysogenic cycle
2. Latent state
3. modified and continues to multiply

Question 22

What are the 3 potential outcomes of lysogeny?

Answer 22

1. immune to reinfection (depending on external conditions)
2. Phage conversion: host cells exhibit new porperties
3. Specialized transduction: Changes genetic properties of the recipient bacteria

Question 23

what happens in lysogeny (latency)?

Answer 23

phage remains latent; no lysis of host cell (non-productive cycle)

Question 24

1. Lysogeny begins like the lytic cycle
   ▪ Adsorption
   ▪ Penetration, then
   * _______________
2. Inserted phage DNA is known as a what?
3. T or F, the host cell replicates its chromosome but not its prophage DNA

Answer 24

1. Incorporation
2. prophage
3. False, replicates its chromosome AND prophage DNA

Question 25

How do bacteriophages get nucleotides and amino acids if they don’t have any metabolic enzymes?

Answer 25

from the hosts

Question 26

Vibrio cholerae produces toxin and is capable of causing cholera only when it is lysogenic. What does this mean?

Answer 26

virus came from the genome which is why it becomes pathogenic

Question 27

In the attachment stage of VIRULENT INFECTIONS of bacteriophages and animal viruses what is the difference?

Answer 27

animal viruses: fusion of viral envelope and host membrane. Bacteriophages: No fusion occurs in bacteriophages

Question 28

In the entry stage of VIRULENT INFECTIONS, what enters the cell in bacteriophages? animal viruses?

Answer 28

Bacteriophage: only nucleic acid animal: entire virion cell including enzymes

Question 29

Animal viruses 1. where do DNA viruses replicate their DNA using host enzymes? 2. Where do they synthesize capsid proteins using host cell enzymes?

Answer 29

1. nucleus of the host 2. cytoplasm

Question 30

What does the outcome of infection of eukaryotic cells depend on?

Answer 30

factors independent of cell

Question 31

In bacteriophages and animal viruses is Targetting of virion necessary? if so what occurs?

Answer 31

Bacteriophage: unnecessary animal: yes, site of replication

Question 32

Where does the uncoating stage of VIRULENT INFECTIONS take place in Bacteriophages and animal viruses?

Answer 32

bacteriophages: surface of cell animal: inside cell

Question 33

_______ _______ has the same pattern of replication as phage with the same genome, (bacteriophages or animal viruses)

Answer 33

animal viruses

Question 34

When viruses may develop relationships with normal hosts but no obvious disease or damage is caused to host this is referred to as?

Answer 34

State of balanced pathogenicity

Question 35

Relationships between viruses and host are divided into what two categories?

Answer 35

* Acute * Persistent

Question 36

Persistent infections can be divided into what 3 categories?

Answer 36

– Latent infections – Chronic infections – Slow infections

Question 37

T/F in acute infections Host cells usually die and may or may not lyse to release virions

Answer 37

TRUE

Question 38

1. In which type of infection can the Infectious virus be detected at all times? 2. T or F Disease may be present or absent during extended times or may develop late in chronic infections? 3. After the initial infection with or without disease symptoms, what happens to the virus? 4. Best known example of a chronic infection?

Answer 38

1. Chronic infections 2. True 3. Virus is released from host with no symptoms 4. * Hepatitis B– a.k.a serum hepatitis

Question 39

In latent infections, infection is followed by what?

Answer 39

symptomless period

Question 40

Hep B, Hep C, and Rubella virus are all what type of infections?

Answer 40

Chronic infections

Question 41

What is responsible for most virus-induced tumors in humans? Cancers caused by DNA viruses result from what? -is growth controlled or uncontrolled?

Answer 41

Double-stranded DNA viruses integration of viral genome onto host DNA - uncontrolled growth

Question 42

1. In slow infections the Infectious agent gradually increases in amount over a (short or long) period of time with no significant symptoms apparent during this time 2. T or F Few infectious agents cause slow infections?

Answer 42

1. Long 2. True

Question 43

1. What is a viroid? 2. What do viroid's consist of? 3. What do viroid's not have that allows them to be resistant to protease?

Answer 43

1. group of pathogens much smaller and distinctly different from viruses 2. small single-stranded RNA molecule 3. no protein coat

Question 44

Define virion

Answer 44

Mature virus particle that is infectious

Question 45

In persistent infections, how are viruses released?

Answer 45

budding

Question 46

________: a protein and genome _________: a single stranded RNA molecule (contains NO protein)

Answer 46

Virion Viroid

Question 47

Define proteus Are virions or viroids more susceptible to proteus?

Answer 47

An enzyme that destroys protein Virions because they contain proteins

Question 48

Define prions T/F prions cause brain degeneration

Answer 48

Proteinaceous infectious agent (infectious proteins) TRUE

Question 49

What is a method for studying viruses?

Answer 49

cultivation of host