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VIRUS PROPERTIES. Infectious – must be transmissible horizontally Intracellular – require living cells RNA or DNA genome, not both* Most all have protein coat * May of may not have lipid envelope May have broad or narrow host range

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VIRUS PROPERTIES


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virus properties
VIRUS PROPERTIES
  • Infectious – must be transmissible horizontally
  • Intracellular – require living cells
  • RNA or DNA genome, not both*
  • Most all have protein coat*
  • May of may not have lipid envelope
  • May have broad or narrow host range
  • Replication involves eclipse (breaking apart of virus particles) and reassembly
  • Use host factors for to complete replication cycle
some consequences and effects of virus infection
SOME CONSEQUENCES AND EFFECTS OF VIRUS INFECTION
  • Like other life forms, viruses promote the propagation of their own kind
  • Like other life forms, virusesevolve in response to selection pressure
  • Viruses are major factors in promoting the evolution of higher organisms
  • Viruses help control populations of their hosts, including humans
virus like agents classified and studied with viruses
Virus-like agents classified and studied with viruses
  • Viroids
    • No coat protein, no coding capacity
  • Prions
    • No nucleic acid (?)
  • Retrotransposons
    • No infectivity (?)
host properties influence the virus types found in that host group
Host properties influence the virus types found in that host group
  • Vertebrates have broad range of viruses
  • Plants have mostly small RNA viruses
  • Fungi have mostly dsRNA viruses
  • Single-celled organisms have mostly large dsDNA viruses
slide5

Viruses are

submicroscopic intracellular

pathogens

slide6

Sizes of microscopic and submicroscopic biological entities

and their ability to be examined using various technologies

Flint et al., 2004

Principles of Virology

Fig. 1.8

viruses may be simple or complex
Viruses may be simple or complex
  • Genome sizes 0.3 - 1200 kb; average genome sizes vary with host organism types
  • Isometric particle sizes vary from ~24 nm to ~400 nm diameter
  • May have single-stranded (ss) or double-stranded (ds) RNA or DNA genome
  • If ssRNA, may be + or – sense
  • May have one or many proteins in particles
  • May or may not have lipid envelope
types of viral genomes
Types of viral genomes
  • double-stranded (ds) DNA
    • Rarely segmented
    • Often large
  • single-stranded (ss) DNA
    • Rarely large
    • Less common than dsDNA
  • ssRNA, negative sense
    • Often found in viruses with broad host ranges
  • ssRNA, positive sense
    • Most common overall
  • dsRNA
    • Often segmented
    • Particle structure often critical
composition of viruses infecting different hosts
Composition of viruses infecting different hosts
  • No “rules” about virus families that may or may not be present in a given kingdom
  • Some types of viruses are found more commonly in some kingdoms than in others
    • Many plant viruses contain ssRNA genomes
    • Many fungal viruses contain dsRNA genomes
    • Many bacterial viruses contain dsDNA genomes
  • Host properties determine the types of viruses that tend to be found in members of a biological “kingdom”
slide10

Virus types by nucleic acid composition

DNA RNA

ss ds ss ds

env naked env naked env naked env naked

Families

Species

0 5 9 12 9 14 2 5

0 100 200 300 200 600 10 300

Host type

Vertebrate

Invertebrate

Plant

Fungus

Bacteria

- + ++ ++ ++ ++ - ++

- + ++ - ++ ++ - ++

- ++ - + + +++ - +

- - - + + + + +++

- + + +++ - + + -

overview of virus properties
Animal

RNA – 5-30 kb

DNA: 5-350 kb

Many enveloped

Range of complexity

Range of morphologies

Some divided genomes

  • True Fungi
    • RNA – 2.5-28 kb
    • DNA – none
    • Enveloped ones have no capsid
    • Little genome complexity
    • Little morphological complexity
    • Some divided genomes
  • Plant
    • RNA – 0.3-28 kb
    • DNA – 3-10 kb
    • Few enveloped
    • Little genome complexity
    • Little morphological complexity
    • Many divided genomes
Overview of Virus Properties
  • Prokaryote
    • RNA – 5-8 kb
    • DNA – 10-200 kb
    • Few enveloped
    • Range of complexity
    • Range of morphologies
    • Few divided genomes
  • Lower eukaryote
    • RNA – 5-10 kb
    • DNA – 180-1200 kb
    • Internal envelope
    • Range of complexity
    • Range of morphologies
    • No divided genomes
tobacco mosaic virus a typical small rna virus
Tobacco mosaic virus – a typical small RNA virus
  • 18X300 nm
  • Single 6400 nt RNA
  • 2130 copies of single 17 kDa coat protein
  • 3 essential genes
  • Simple regulatory elements
poxvirus a typical large dsdna virus
Poxvirus – a typical large dsDNA virus
  • 120X200 nm
  • Single 180 kb DNA
  • Complex coat made up of numerous proteins
  • >100 essential genes
  • Complex regulatory elements
virus at the edge mimivirus
Virus at the edge: Mimivirus
  • Mimivirus infects Acantamoeba polyphaga
  • 400 nm particle, 1.2 megabase genome, 1262 putative ORFs represent the largest virus identified yet
  • Many genes for normal cellular functions
    • central translation functions
      • Aminoacyl tRNA synthetases
      • Peptide release factor 1
      • Translation elongation factor EF-TU
    • DNA repair enzymes
    • Many polysaccharide synthesis enzymes
  • Lineage suggests connection with eukaryotes, not prokaryotes

Raoult et al., Science Express 10/14/04

slide15

Phylogenetic position of Mimivirus

Compared to other similar DNA viruses

Compared to other prokaryotic and eukaryotic life forms

Raoult et al., Science Express 10/14/04

slide16

Mimiviruses (arrowed) can bee seen inside their amoeba host, Acanthamoeba polyphaga using a light microscope

Raoult et al., Science Express 10/14/04

slide17

By transmission electron microscopy, isolated Mimivirus can be seen as a large icosahedral virus with fibrilar protrusions

Mimivirus (green) seen by fluorescence microscopy in amoeba

Mimivirus in ultrathin section in amoeba

Raoult et al., Science Express 10/14/04

slide18

At 1.2 megabases (1.2X106 nucleotides), Mimivirus has the largest genome of any known virus, larger than many bacteria

slide19

Simple virus replication cycle

  • Virus enters
  • host cell

5. New virus released from host cell

2. RNA released;

translates

3. Replication in cytoplasm

4. New virus assembled

slide20

From 7th

Report of the

ICTV

(Academic

Press, 2000)

slide21

From 7th

Report of the

ICTV

(Academic

Press, 2000)

slide22

From 7th

Report of the

ICTV

(Academic

Press, 2000)

slide23

From 7th

Report of the

ICTV

(Academic

Press, 2000)

slide24

From 7th Report of the ICTV

(Academic Press, 2000)

slide25

From 7th Report of the ICTV

(Academic Press, 2000)

slide26

From 7th Report of the ICTV

(Academic Press, 2000)

slide27

From 7th Report of the ICTV

(Academic Press, 2000)

slide28

From 7th Report

of the ICTV

(Academic

Press, 2000)

slide29

From 7th Report

of the ICTV

(Academic

Press, 2000)