Virus Structure, Classification, and Life Cycle

Question 1

What are filterable agents and how did the name come about?

Answer 1

Filterable agents are viruses. The name came about when these organisms could filter through 220nm pores. Hence, bacteria are bigger than 220nm while viruses are smaller than 220 nm because bacteria were trapped by the filter and filtrate was not infectious while the viruses went thru and filtrate remains infectious.

Question 2

Order in terms of size from largest to smallest, ribosomes, atoms, proteins, viruses, animal cells, plant cells, eyes, bacteria

Answer 2

1. eyes
2. plant cells
3. animal cells
4. bacteria
5. viruses
6. ribosomes
7. proteins
8. atoms

Question 3

T/F: viruses are associated with all life forms

Answer 3

True

Question 4

Definition of a virus

Answer 4

a capsid-encoding organism that has a genome

Question 5

what is a capsid?

Answer 5

protein shell that encapsulates the nucleic acid genome

Question 6

what is a virion?

Answer 6

the particle encoded by a virus genome

Question 7

All viruses have these 3 basic gene modules

Answer 7

1. capsid proteins
2. replicon (encodes the nucleic acid polymerase and accessory proteins to copy the genome)
3. host-cell interacting factors

Question 8

What are the non-structural and structural proteins in viruses?

Answer 8

non-structural proteins = host-cell interacting factors

structural proteins = capsid proteins

Question 9

Virions contain which basic gene modules

Answer 9

genome and capsid

Question 10

T/F: The capsid shape and genome type are dependent

Answer 10

False: the capsid shape and genome type are independent

Question 11

What are 3 ways to classify viruses?

Answer 11

1. host cell (kingdom)
2. genome type (RNA or DNA; single or double stranded)
3. virion structure (enveloped or naked; icosahedral, helical or complex)

Question 12

State the genome type, the structure and whether it’s enveloped or not: Adenovirus

Answer 12

1 -dsDNA

2. icosahedral
3. naked

Question 13

State the genome type, the structure and whether it’s enveloped or not: Poxvirus

Answer 13

1. dsDNA
2. complex
3. enveloped

Question 14

State the genome type, the structure and whether it’s enveloped or not: Influenza Virus

Answer 14

1. • segmented RNA
2. helical
3. enveloped

Question 15

State the genome type, the structure and whether it’s enveloped or not: Herpesvirus

Answer 15

1. dsDNA
2. icosahedral
3. enveloped

Question 16

State the genome type, the structure and whether it’s enveloped or not: Retrovirus

Answer 16

1. • ssRNA (2 copies b/c diploid)
2. icosahedral
3. enveloped

Question 17

All viruses share this simple 3-part strategy to ensure their survival

Answer 17

1. The genome encodes a capsid that protects it outside the cell
2. The genome contains info for infecting a cell, replicating the genome, intraceullar survival, and assembling virions
3. Transmission to a new host is required to maintain the virus as a species

Question 18

What type of microscope is used to observe viruses and cell cultures?

Answer 18

Inverted microscopes because viruses are NOT visible by light microscopy

Question 19

Virus infection may cause ______________ that can be used to study virus replication and infectivity.

Answer 19

cytopathic effects

Question 20

What are 6 things viruses need to grow?

Answer 20

1. The right host (tropism)
2. Cells with the right receptors (susceptible)
3. Appropriate intracellular environment (permissive)
4. Biosynthetic machinery
5. Abundant building blocks (RNA, DNA, amino acids, ATP, lipids, sugars, etc.
6. Time to finish replication

Question 21

What are the 9 general steps in virus replication?

Answer 21

1. Recognition
2. Attachment
3. Entry: Penetration or Fusion
4. Cell coating
5. Transcription, making more mRNA
6. Protein translation
7. Replication of the genome
8. Assembly of virions
9. Egress: lysis, budding, or exocytosis

Question 22

Define host range

Answer 22

The preferred species

Question 23

Define abortive infection

Answer 23

replication is incomplete

Question 24

Define tissue tropism

Answer 24

the preferred cell type

Question 25

Which step of viral replication marks the beginning of eclipse phase?

Answer 25

Uncoating

Question 26

Viruses can uncoat in these regions

Answer 26

At the plasma membrane, within endosomes, at the nuclear pore

Question 27

T/F: All viruses must make mRNA

Answer 27

True

Question 28

T/F: Only host transcription factors regulate transcription of viral genome

Answer 28

False; both viral and host transcription factors regulate mRNA synthesis

Question 29

Viral mRNAs are translated into protein by host machinery, requiring these 3 host components

Answer 29

- ribosomes - tRNAs - Amino acids

Question 30

How are viral proteins sorted?

Answer 30

They are sorted to site of virion assembly. Capsid proteins interact with newly made genomes. Membrane proteins traffic thru secretory pathway and cytosolic proteins accumulate next to membrane

Question 31

T/F: Polymerases make new genomes using host cell nucleotides

Answer 31

True

Question 32

Which polymerase is unique to viruses?

Answer 32

RNA-dependent RNA polymerase (RDRP) -makes mRNA and genomes

Question 33

What marks the end of eclipse phase?

Answer 33

Assembly of virions so eclipse phase is from uncoating of capsid to assembling of virions

Question 34

Do viral DNA get inserted into capsid as it's growing or after the capsid has been made.

Answer 34

Viral DNA is inserted after the capsid shell has been made already.

Question 35

Where do enveloped viruses acquire their lipid bilayer?

Answer 35

membranes from ER, Golgi, Plasma membrane

Question 36

T/F: All virion components accumulate at the site of capsid formation, genome incorporation, matrix, glycoproteins, and envelopment

Answer 36

True

Question 37

How can virions transfer to new cells?

Answer 37

by syncytium formation

Question 38

The entry of enveloped viruses into cells involves

Answer 38

fusion between viral and cellular membranes

Question 39

T/F: Virion envelopes are constructed from viral glycoproteins and host membranes

Answer 39

True

Question 40

T/F: Exocytosis of enveloped virions occurs in a burst and lyses the cell.

Answer 40

False