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Microbiology > 14. Virion structure general composition and symmetry > Flashcards

14. Virion structure general composition and symmetry Flashcards

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Biology 101 flashcards
1
Q

Are viruses alive

A

No. They are unable to carry out metabolic reactions outside a host cell

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2
Q

What are definition and properties of a virus

A

Viruses are filterable agents that are obligate intracellular parasites. They can’t make energy or proteins independently from a host cell.
They have a naked capsid or envelope morphology

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3
Q

Can viral genome be both RNA and DNA

A

No, only one or the other

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4
Q

Do virus components replicate by division

A

No

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5
Q

What are the consequences of viral properties

A

Aside for not being living things, they need to be infectious to endure in nature. They mist be able to use host cell to produce their components and they must encode any required processes not provided by the cell. Viral components must self-assemble

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6
Q

Where can viruses exist

A

Extracellularly or intracellularly

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7
Q

What happens to viruses when they are extracellular

A

They are inactive because they can’t reproduce outside a host cell

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8
Q

What happens to viruses when they are intracellular

A

They commandeer host cells and use them to synthesize viral components from which mature progeny viruses are assembled and eventually released

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9
Q

Who can viruses infect

A

-Eukaryotes( animals, plant, fungi)
-Bacteria and Archaea
-Other viruses( viriophages)

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10
Q

On what properties can we do virus classification

A

-Genome type
-Virion structure
-Replication strategy

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11
Q

What’s virus classification by genome type

A

-Type of nucleic acid(DNA or RNA)
-Double helix or single helix and polarity
-Unsegmented or segmented
-Linear or circular
–If the genome is diploid( retroviridae)

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12
Q

What’s virus classification by virion structure

A

-Capsid symmetry: icosahedral, helical, complex
-Number of capsomeres
-Presence or absence of envelope

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13
Q

What’s classification of viruses by replication strategy

A

It’s shown by Baltimore classification system where:
1. dsDNA->mRNA
2.ssDNA->dsDNA->mRNA
3.dsRNA->mRNA
4.(+)ssRNA->(-)ssRNA->mRNA
5.(-)ssRNA->mRNA
6.(+)ssRNA->DNA/RNA hybrid->dsDNA->mRNA
7.dsDNA->ssRNA->mRNA

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14
Q

In what taxa can viruses be divided in

A

-Orders(-virales)
-Families(-viridae)
-Subfamilies(-virinae)
-Genus(-virus)
-Species
-Strains
-Types

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15
Q

What characteristics do viruses of the same specie share

A

They infect same host or a tissue, cause the same pathology and have same genomic map

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16
Q

What about genotypes of viruses?

A

Genotypes posses nucleotide differences that do not result in antigenic differences

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17
Q

What about serotypes of viruses

A

Serotypes differ in the presence of specific epitopes- are neutralized by different antibodies

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18
Q

What are viral strains

A

Viral isolates that have been well defined; like laboratory strains

19
Q

How is mature virus particle called

A

Virion; it’s infectious( able to infect a cell)

20
Q

What do the simplest virions consist of

A

-nucleocapsid(composed of nucleic acid, either DNA or RNA)
-protein ccoat-capsin

21
Q

What does capsid do

A

It surrounds viral nucleic acid, thereby protecting the genome and often aids in its transfer between host cells

22
Q

How can viruses be classified based on the envelope

A

.Enveloped viruses-virions covered by a lipid membrane
-Nonenveloped or naked viruses- viruses lacking the lipid membrane

23
Q

What’s missing from the viruses

A

Ribosomes( for protein synthesis ) and mechanism for generating ATP. Cytoplasm is absent, and there is not enough enzymes (if any at all) to sustain cellular processes

24
Q

What is virion structure defined by

A

Capsid symmetry and presence or absence of envelope

25
Q

How do nonenveloped viruses construct a capsid

A

From many copies of one protein and a few minor proteins. Each subunit is named protomer and thousands of protomers self-assemble to form the capsid

26
Q

How do enveloped viruses form a capsid

A

They require both nucleocapsid proteins and additional proteins to anchor the membrane. Some viruses use noncapsid proteins as scaffolding upon which the capsids are assembled

27
Q

What are helical capsids and give example

A

They are capsids shaped like hollow tubes with protein walls. One of the examples is tobacco mosaic virus

28
Q

How does TMV assemble its helical capsid

A

Self-arrangement of TMV protomers into helical arrangement produces a rigid tube. Capsid encloses a genome, which is wound in a spiral and lies within a groove formed by the protein subunits

29
Q

What kind of nucleic acid does helical capsid contain

A

RNA

30
Q

What are other examples, except TMV of helical viruses

A

Rabies virus, Ebola, influenza

31
Q

What is icosahedral

A

Regular polyhedron with 20 equilateral triangular faces and 12 vertices

32
Q

Characteristics of icosahedral capsid

A

It’s the most efficient way to enclose a space. They are structured from ring- or knob-shaped assemblages of 5 or 6 protomers, the assemblages are called caspomers

33
Q

What are capsomers composed of 5 and 6 protomers called

A

Pentons and hexons( hexamers)

34
Q

Are hexomeras in every icosahedral capsid

A

No, but pentamers are

35
Q

With what does number of exons vary

A

With size of a virus

36
Q

Give example of viruses based on number of exons

A

0- Parvovirus B19
20- Polioviruses
60- Papillomaviruses
150- Epstein and Barr viruses
240- Adenoviruses

37
Q

What are examples of viruses with complex symmetry

A

Poxviruses and large bacteriophages

38
Q

What are characteristics of poxviruses

A

They are among the largest of the animal viruses and can be seen with the light microscope. they have complex internal structure with an ovoid to brick shaped exterior

39
Q

What is virion morphology of poxvirus

A

Its double-stranded DNA genome is associated with proteins and contained in the core, a central structure shaped like biconcave disk and surrounded by a membrane. Two lateral bodies lie between the core and the virion’s outer envelope and contain viral enzymes

40
Q

What’s characteristic of virions of some phages

A

Virions of T2,T4 and T6 phages8even phages) that infect Escherichia coli are said to have binal symmetry because they have a head that resembles an icosahedron and a helical tail

41
Q

What’s different about the head of T-even phages

A

Icosahedral head is elongated by one or two rows of hexamers in the middle and contains the DNA genome

42
Q

What is characteristic for the tail of T- even phages

A

Tail is composed of a collar joining it to the head, a central hollow tube, a sheath surrounding a tube and a complex baseplate

43
Q

What’s characteristic for a baseplate of T-even phages

A

Baseplate is hexagonal and has a pin and a jointed long tail fiber and a short tail fiber at each corner

44
Q

What are examples of icosahedral and helical viruses with and without envelope

A

Icosahedral without envelope: poliovirus ,adenovirus, hepatitis A virus
Helical without envelope: TMV; no human virus is found here
Icosahedral w envelope: herpesvirus
Helical w envelope: rabies virus, flu virus

Microbiology (20 decks)

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