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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
Q

From where is the envelope of a virus acquired?

A

From the host cell during replication

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26
Q

Where on an enveloped virus are virally encoded glycoproteins or ‘spikes’ found?

A

Protruding outward from the envelope’s surface

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27
Q

What role do viral spike proteins play in the life cycle of the virus?

A

The virion’s recognition of host cells

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28
Q

Why are enveloped viruses more fragile than naked ones?

A

Membranes are more susceptible to detergents, alcohol, and drying

29
Q

What type of bacteriophage replication results in lysis of the cell near the end of the cycle?

A

Lytic replication

30
Q

Describe the attachment stage in the lytic replication cycle of the bacteriophage T4

A

The virion attaches to the host cell

31
Q

Describe the entry stage in the lytic replication cycle of the bacteriophage T4 (2)

A
  • The virion enters the host cell
  • Viral enzymes degrade the bacterial chromosome
32
Q

Describe the synthesis stage in the lytic replication cycle of the bacteriophage T4

A

Ribosomes are used to synthesize new viral nucleic acids and proteins

33
Q

Describe the assembly stage in the lytic replication cycle of the bacteriophage T4

A

New virions are spontaneously assembled in the host cell

34
Q

Describe the release stage in the lytic replication cycle of the bacteriophage T4

A

New virions are released form the host cell

35
Q

What role does lysozyme play during entry and release?

A

It pre-weakens the peptidoglycan of the cell wall prior to entry / release

36
Q

What type of bacteriophage replication involves a ‘modified’ cycle in which infected host cells grow and reproduce normally for many generations before they lyse?

A

Lysogenic replication / lysogeny

37
Q

What type of phages are involved in the lysogenic replication cycle?

A

Temperate phages

38
Q

Virulent phages strictly follow the ______

A

Lytic replication cycle

39
Q

After entry into the host cell, the viral genome remains ______

40
Q

What is a prophage?

A

An inactive phage

41
Q

In reference to the lysogenic life cycle of bacteriophage lambda, what is induction? (3)

A
  • A prophage is inserted into DNA
  • Becomes part of the bacterial chromosome
  • Passed on to daughter cells
42
Q

Describe the concept of lysogenic conversion

A

Changing the phenotype of a bacterium from harmless into a pathogen

43
Q

Name the 3 different mechanisms by which animal viruses enter a host cell

A
  • Direct penetration
  • Membrane fusion
  • Endocytosis
44
Q

Describe direct penetration (2)

A
  • Naked viruses enter the host cell
  • Creates a pore for the genome to enter
45
Q

Describe membrane fusion (2)

A
  • The entire nucleocapsid enters the host cell
  • The envelope and host cell membrane fuse
46
Q

During membrane fusion, ______ are left as part of the cell membrane

A

Envelope glycoproteins

47
Q

Describe endocytosis (3)

A
  • Enveloped viruses / naked viruses enter the host cell
  • Virus attaches to receptor molecules
  • The cell endocytizes the virus
48
Q

For animal viruses, what is uncoating?

A

Removal of the capsid from the nucleocapsid

49
Q

When does uncoating occur?

A

Membrane fusion

50
Q

What is budding?

A

Enveloped animal viruses are released into the environment

51
Q

What is viral budding?

A

Viral glycoproteins are inserted into cellular membranes

52
Q

Infections with enveloped viruses in which host cells shed viruses slowly and steadily are known as ______

A

Persistent infections

53
Q

Budding allows an infected cell to …

A

Remain alive

54
Q

Name 2 examples of latent viruses / proviruses

A
  • Chicken Pox
  • Herpes
55
Q

Latent viruses ______ become incorporated into the chromosomes of their host cells

56
Q

Lysogenic phases ______ become incorporated into the chromosomes of their host cells

57
Q

When a provirus is incorporated into its host DNA, the condition is ______

58
Q

What are viroids?

A

Circular pieces of ssRNA that are pathogenic in plants

59
Q

How are viroids different from RNA viruses? (2)

A
  • Lack capsids
  • Do NOT code for proteins
60
Q

Describe the mechanism by which viroids cause plant diseases (3)

A
  • Adhere to plant mRNA
  • Forms dsRNA
  • Plant enzymes degrade
61
Q

Name an example of a plant disease caused by viroids

62
Q

What are prions?

A

Proteinaceous infectious particles

63
Q

Where is mammalian PrP protein found?

A

Mammal brain cells

64
Q

Describe ‘cellular’ PrP regarding form and function

A

Normal functional structure with a-helices

65
Q

Describe ‘prion’ PrP regarding form and function

A

Disease-causing form with b-pleated sheets

66
Q

What is templating?

A

PrP acts as a template to refold molecules of cellular PrP

67
Q

Describe prion diseases in terms of systems affected and cellular changes (2)

A
  • Fatal neurological degeneration
  • Formation of large vacuoles
68
Q

Why are prion diseases called spongiform encephalopathies?

A

Neurological degeneration results in a spongy appearance

69
Q

Name an example of a spongiform encephalopathies disease

A

Bovine spongiform encephalitis

MICRB 106 - Exam 4 (4 decks)

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