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MICRB 106 - Exam 4 > Characterizing / Classifying Viruses, Viroids, and Prions > Flashcards

Characterizing / Classifying Viruses, Viroids, and Prions Flashcards

1
Q

Why are viruses known as acellular infectious agents?

A

They have no cytoplasmic membrane, cytosol, or functional organelles

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2
Q

Which characteristics of life do viruses lack? (4)

A
  • Growth
  • Reproduction
  • Responsiveness
  • Metabolism
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3
Q

What term is used to refer to a virus in its complete or extracellular form?

A

Virion

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4
Q

What is the minimum basic structure / organization of all viruses?

A

Capsids

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5
Q

What are capsids?

A

Protein coats made of capsomeres surrounding a nucleic acid core

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6
Q

What are capsomeres?

A

Outer subunit of a capsid

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7
Q

What are nucleocapsids?

A

Nucleic acids and their capsids

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8
Q

What is a viral envelope?

A

Phospholipid membranes surrounding the nucleocapsid of a virion

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9
Q

What are the 2 functions imparted by the outermost layer of a virion?

A
  • Protection
  • Host-pathogen specificity
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10
Q

Name the 4 different kinds of viral genomes

A
  • Single-stranded RNA (ssRNA)
  • Single-stranded DNA (ssDNA)
  • Double-stranded RNA (dsRNA)
  • Double-stranded DNA (dsDNA)
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11
Q

Are viral genomes typically larger or smaller than cellular genomes?

A

Smaller

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12
Q

What kinds of organisms are susceptible to viral attack?

A

All types of organisms

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13
Q

______ are viruses that infect bacteria

A

Bacteriophages

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14
Q

Are viruses bigger or smaller than bacteria?

A

Smaller

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15
Q

Virus is latin for ______

A

Poison

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16
Q

Capsomeres that spiral around the nucleic acid are called ______

A

Helical viruses

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17
Q

Describe the shape of helical viruses

A

Tube-like structure

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18
Q

Describe the shape of polyhedral viruses

A

Spherical dome shape

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19
Q

Describe the shape of complex viruses

A

Capsids of many different shapes

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20
Q

Describe icosahedral heads

A

Genome attached to helical tails

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21
Q

______ refers to an outer membrane of a virus that is similar in composition to a cell membrane

A

Envelope

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22
Q

______ refers to a virus that possesses an envelope

A

Enveloped virions

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23
Q

______ refers to a virus that does not possess an envelope

A

Nonenveloped / naked virions

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24
Q

What is the viral envelope composed of?

A

Phospholipid bilayer and embedded proteins

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25
From where is the envelope of a virus acquired?
From the host cell during replication
26
Where on an enveloped virus are virally encoded glycoproteins or ‘spikes’ found?
Protruding outward from the envelope’s surface
27
What role do viral spike proteins play in the life cycle of the virus?
The virion’s recognition of host cells
28
Why are enveloped viruses more fragile than naked ones?
Membranes are more susceptible to detergents, alcohol, and drying
29
What type of bacteriophage replication results in lysis of the cell near the end of the cycle?
Lytic replication
30
Describe the attachment stage in the lytic replication cycle of the bacteriophage T4
The virion attaches to the host cell
31
Describe the entry stage in the lytic replication cycle of the bacteriophage T4 (2)
- The virion enters the host cell - Viral enzymes degrade the bacterial chromosome
32
Describe the synthesis stage in the lytic replication cycle of the bacteriophage T4
Ribosomes are used to synthesize new viral nucleic acids and proteins
33
Describe the assembly stage in the lytic replication cycle of the bacteriophage T4
New virions are spontaneously assembled in the host cell
34
Describe the release stage in the lytic replication cycle of the bacteriophage T4
New virions are released form the host cell
35
What role does lysozyme play during entry and release?
It pre-weakens the peptidoglycan of the cell wall prior to entry / release
36
What type of bacteriophage replication involves a ‘modified’ cycle in which infected host cells grow and reproduce normally for many generations before they lyse?
Lysogenic replication / lysogeny
37
What type of phages are involved in the lysogenic replication cycle?
Temperate phages
38
Virulent phages strictly follow the ______
Lytic replication cycle
39
After entry into the host cell, the viral genome remains ______
Inactive
40
What is a prophage?
An inactive phage
41
In reference to the lysogenic life cycle of bacteriophage lambda, what is induction? (3)
- A prophage is inserted into DNA - Becomes part of the bacterial chromosome - Passed on to daughter cells
42
Describe the concept of lysogenic conversion
Changing the phenotype of a bacterium from harmless into a pathogen
43
Name the 3 different mechanisms by which animal viruses enter a host cell
- Direct penetration - Membrane fusion - Endocytosis
44
Describe direct penetration (2)
- Naked viruses enter the host cell - Creates a pore for the genome to enter
45
Describe membrane fusion (2)
- The entire nucleocapsid enters the host cell - The envelope and host cell membrane fuse
46
During membrane fusion, ______ are left as part of the cell membrane
Envelope glycoproteins
47
Describe endocytosis (3)
- Enveloped viruses / naked viruses enter the host cell - Virus attaches to receptor molecules - The cell endocytizes the virus
48
For animal viruses, what is uncoating?
Removal of the capsid from the nucleocapsid
49
When does uncoating occur?
Membrane fusion
50
What is budding?
Enveloped animal viruses are released into the environment
51
What is viral budding?
Viral glycoproteins are inserted into cellular membranes
52
Infections with enveloped viruses in which host cells shed viruses slowly and steadily are known as ______
Persistent infections
53
Budding allows an infected cell to …
Remain alive
54
Name 2 examples of latent viruses / proviruses
- Chicken Pox - Herpes
55
Latent viruses ______ become incorporated into the chromosomes of their host cells
DO NOT
56
Lysogenic phases ______ become incorporated into the chromosomes of their host cells
DO
57
When a provirus is incorporated into its host DNA, the condition is ______
Permanent
58
What are viroids?
Circular pieces of ssRNA that are pathogenic in plants
59
How are viroids different from RNA viruses? (2)
- Lack capsids - Do NOT code for proteins
60
Describe the mechanism by which viroids cause plant diseases (3)
- Adhere to plant mRNA - Forms dsRNA - Plant enzymes degrade
61
Name an example of a plant disease caused by viroids
Stunting
62
What are prions?
Proteinaceous infectious particles
63
Where is mammalian PrP protein found?
Mammal brain cells
64
Describe ‘cellular’ PrP regarding form and function
Normal functional structure with a-helices
65
Describe ‘prion’ PrP regarding form and function
Disease-causing form with b-pleated sheets
66
What is templating?
PrP acts as a template to refold molecules of cellular PrP
67
Describe prion diseases in terms of systems affected and cellular changes (2)
- Fatal neurological degeneration - Formation of large vacuoles
68
Why are prion diseases called spongiform encephalopathies?
Neurological degeneration results in a spongy appearance
69
Name an example of a spongiform encephalopathies disease
Bovine spongiform encephalitis

MICRB 106 - Exam 4 (4 decks)

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