Chapter 33: Viruses

Question 1

Describe the hereditary material in viruses vs living organisms.

Answer 1

viruses: DNA or RNA, single or double stranded
organism: DNA and always double stranded

Question 2

Describe the plasma membrane in viruses vs living organisms.

Answer 2

viruses: no membrane
organisms: have membrane

Question 3

Describe transcription in viruses vs living organisms.

Answer 3

viruses: doesn’t occur
organisms: occurs

Question 4

Can viruses carry out translation independently?

Answer 4

no

Question 5

All viruses contain…

Answer 5

1. genetic material (DNA or RNA)
2. capsid

some contain an outer phospholipid membrane called an envelope

Question 6

Describe the variety of viral genomes.

Answer 6

• linear or circular
• DNA or RNA
• single-stranded (ss) or double-stranded (ds)
• options are dsDNA, ssDNA, dsRNA, or ssRNA

Question 7

What are the 3 categories of ssRNAs?

Answer 7

1. positive sense
2. negative sense
3. abisense

Question 8

What is positive sense?

Answer 8

sequence matches the mRNA, so its directly read by the ribosomes to synthesize proteins

Question 9

What is negative sense?

Answer 9

sequence is complementary to mRNA; must be copied before translation

Question 10

What is ambisense?

Answer 10

part of genome is pos sense, the other is negative sense

Question 11

What is the viral growth cycle also referred to as?

Answer 11

lytic cycle because it ends with lysis of bacterial host cell

Question 12

Describe the 6 phases of the lytic cycle.

Answer 12

1. viral genome enters the host bacterial cell
2. viral genome transcribed to produce viral proteins (gene expression)
3. viral genome replicated
4. particles assemble inside host
5. particles exit to exterior
6. free virions in tissue or environment are transmitted to new host

Question 13

Viruses enter a cell via _________.

Answer 13

uncoating

Question 14

What is uncoating?

Answer 14

viral capsid is removed and the genome is released

Question 15

What are the two mechanisms enveloped viruses follow ?

Answer 15

1. viral proteins bind to a receptor causing the viral membrane to fuse with the cell membrane
2. virions enter via endocytosis; acidification causes viral proteins to change shape, promoting release

Question 16

What are the classes of DNA viruses?

Answer 16

1. Class I: dsDNA
2. Class II: ssDNA

Question 17

What are the classes of RNA viruses?

Answer 17

1. Class III: dsRNA
2. Class IV: (+)ssRNA
3. Class V: (-)ssRNA

All require RNA replicase

Question 18

What are the classes of reverse-transcribing viruses?

Answer 18

1. Class VI: (+)ssRNA RT
2. Class VII: dsRNA RT

require reverse transcriptase

Question 19

How are viruses classified?

Answer 19

1. genome and morphology
2. nature of host species
3. how the virus replicated within the host

Question 20

What are antiviral drugs?

Answer 20

designed to target specific viruses at specific stages of infection

Question 21

What are vaccines?

Answer 21

activate immune response