Viruses 1 Flashcards

1
Q

Virus discovery

A

Chamberland filters removed bacteria from extracts
- yet extracts still caused disease
.:. microbe distinct from + smaller than bacteria caused disease

Virus nature + structure defined by electron microscope

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2
Q

What are viruses?

A

Non-cellular parasitic microbes
- w/ no intrinsic metabolic capabilities

Obligate intracellular parasites
- can only replicate inside living host cells

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3
Q

Viral replication

A
  1. Virus attaches host cell
  2. Capsid penetrates cell
  3. Uncoating of capsid
    = DNA released
  4. Viral DNA + proteins synthesised via host machinery
  5. Assembly of new virions
  6. Release + maturation of virions
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4
Q

General characteristics of viruses

A

Simple structures

  • few/no enzymes of their own
  • consist of NAs + protein

Size

  • smaller than almost all microbes
  • 20nm-400nm
  • size of virus unrelated to size of target host cell
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5
Q

Virus structure

A

Capsid encloses genome
- symmetrical

Some have an outer lipid envelope

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6
Q

capsid function

A

protect viral genome

facilitate entry into cell

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7
Q

genome

  • size
  • made of
A

small compared to other orgs

DNA or RNA
(most bacteriophage =DNA
all plant + most animal = RNA)

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8
Q

capsomeres

A

subunit of capsid

capsid mad euphorias of many individual capsomeres

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9
Q

nucleocapsid/core

A

capsid w/ enclosed NAs

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10
Q

tegument

A

space between nucleocapsid + envelope

may contain accessory viral proteins

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11
Q

virion

A

complete mature virus particle

metabolically inert

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12
Q

envelope

A

lipid membrane surrounding complex viruses

may contain glycoproteins

derived from host cell membrane during budding of viruses

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13
Q

capsid

- why are capsomeres a fundamental property?

A

economy of genetic info

ease of capsid assembly

ease of intracellular release of viral genome

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14
Q

economy of genetic info

A

allows virus to generate capsids from min level of genetic info

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15
Q

ease of capsid assembly

A

virus particles can self-assemble
+ held together by intra-molecular forces NOT covalent bonds

.:. no additional enzyme needed to join subunit s

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16
Q

ease of intracellular release of viral genome

A

dissociation of non-covalently bonded capsid

-> easy release of genome inside host

17
Q

capsid symmetry

- types + e.g.s

A

helical
e.g. Tobacco mosaic virus

icosahedral (20 faces)
e.g. Adenovirus

BUT asymmetrical
e.g. Ebola

18
Q

icosahedral capsids

- made up of…

A

20 sided polygon

each of the 12 corners = a penton = a capsomere

each face composed of a heron
= repeating units of same capsomere

hexons + pentons can be identical proteins or distinct

19
Q

helical capsids

  • e.g.
  • arrangement
A

e.g. tobacco mosaic virus (TMV)

capsomeres arranged in helical array to form a helical cylinder

inside surface of each capsomere contains a ridge
- viral genome in embedded

20
Q

helical capsids

- microscopes

A

shape not always evident in microscopes

influenza’s helical capsid appears roughly spherical

21
Q

genome

  • encodes
  • fragmented?
A

all necessary info to direct host cells to make viral proteins + replicate viral genome

some encode genomes on several distinct strands of DNA/RNA

e.g. influenza has a fragmented genome
w/ 8 separate strands of RNA

22
Q

genome

  • size e.g.s
  • overlapping
A

Cauliflower mosaic virus encodes 7 genes
vs E.coli encodes 4000

often encode overlapping genes
- can encode more genes on a smaller strand

23
Q

Classification of viruses

- originally

A

based on diseases caused
- BAD

dissimilar viruses may cause similar symptoms
OR
same virus may cause different symptoms depending on age, health etc of host

symptoms may also be associated with secondary bacterial infections
NOT primary viral infection

24
Q

Hepatitis

- what is it?

A

= inflammation of liver

25
Q

Virus classification

- ICTV base it on

A

genome composition + structure

capsid symmetry

envelope

size

host range

26
Q

Virus classification

- most important component

A

genome

those w/ similar genome sequences likely to share a common ancestry

27
Q

genome

- composition

A

DNA or RNA

ss or ds

ssRNA may either be +ve sense RNA
OR
-ve sense RNA

(copying a +ve sense strand
–> complementary -ve sense strand being synthesised)

28
Q

genome

- +ve snese RNA

A

mRNA needs to be +ve sense to be translated

BUT +ve sense template transcribed into a -ve sense product

SO additional steps required

29
Q

genome classifications

A

Class:
1 = dsDNA

2 = ssDNA + dsDNA

3 = dsRNA

4 = +ssRNA + - ssRNA

5 = -ssRNA

6 = ssRNA-RT + DNA/RNA + dsDNA

7 = dsDNA-RT

30
Q

Baltimore classification of viral genomes

  • group 1
  • group 2
  • group 3
A

dsDNA
- uses own or host DNA pol for replication

ssDNA
- requires DNA pol

dsRNA
- requires RNA-dependent RNA pol to make mRNA + genomic RNA

31
Q

Baltimore classification of viral genomes

  • group 4
  • group 5
A

+ ssRNA
- requires RNA-dependent RNA pol to make mRNA template + replication

  • ssRNA
  • requires RNA-dependent RNA pol to make mRNA + replication
32
Q

Baltimore classification of viral genomes

  • group 6
  • group 7
A

retrovirus
- uses own RTase to make dsDNA

dsDNA pararetrovirus
- requires plant host RTase to make dsDNA

33
Q

Hepatitis

  • envelope Y/N?
  • group
A

Hep A Virus = N
+ve sense ssRNA (gp 4)

Hep B = Y
dsDNA (gp 7)

Hep C = Y
+ve sense ssRNA (gp4)

Hep D = Y
-ve sense ssRNA (gp5)

Hep E = N
+ve sense ssRNA (gp4)