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Viral Biology: Characteristics, Structure, Replication, and Taxonomy of Viruses - Prof. Ba, Study notes of Microbiology

An overview of viruses, including their characteristics, taxonomy, structure, and replication processes. It covers both dna and rna viruses, as well as enveloped and nonenveloped viruses. The document also discusses the role of viruses in causing diseases and the methods used to identify and culture them.

Typology: Study notes

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Slide 1
Viruses
Lecture 16
Slide 2
Biol 240 S06 2
Learning Outcomes
Characteristics of
Viruses
•Viral Taxonomy
•Viral Structure
Viral Replication
•DNA viruses
RNA viruses
•Prions
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pf8
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Slide 1

Viruses

Lecture 16

Slide 2

Biol 240 S

Learning Outcomes

  • Characteristics of

Viruses

  • Viral Taxonomy• Viral Structure• Viral Replication• DNA viruses• RNA viruses• Prions

Slide 3

Biol 240 S

3

Characteristics of ALL Viruses

    1. Viruses contain genetic material
    • Either DNA or RNA never both
        1. Protein coat = Virion• 3. Multiply inside living cells• 4 Cause the synthesis of structures for

their own transfer

Describe the 4 characteristics of all viruses.

Slide 4

Biol 240 S

General Characteristics of Viruses •^

Most viruses infectonly specific types ofcells in one host

-^

Host range isdetermined by specifichost attachmentreceptors

-^

Polio–

Narrow range

•^

Rabies–

Broad host range

What factors determine the host range of viruses.

Slide 7

Biol 240 S

7

Viral Proteins

•^

Enzymes–

DNA or RNA Polymerases

-^

protease

•^

Structural Proteins–

Capsid proteins

-^

Receptors

•^

Antigenicity due to differencein structural proteins–

Serotypes

-^

influenza

•^

Antibodies bind to structuralproteins

-^

Cytotoxic T cells

Slide 8

Biol 240 S

Viral Envelope

•^

Components–

Lipoprotein derivedfrom host cell plasmamembrane

-^

Viral proteins

•^

Protein spikes–

Attach to host cellreceptors for hormones

-^

Glycoproteins

-^

Influenza

-^

Hemagglutin

-^

HIV

-^

Gp 120

•^

Less resistant thannon-enveloped viruses

Provide definitions for the following terms – capsid,nonenveloped virus, enveloped virus, and virion

Slide 9

Biol 240 S

9

Viral Taxonomy

  • Family names end in -viridae• Genus names end in -virus• Viral species: A group of viruses sharing the

same genetic information and ecological niche(host). Common names are used for species

  • Subspecies are designated by a number

Provide an example of a family, genus, species, and acommon name of a virus.

Slide 10

Biol 240 S

Viral Taxonomy

  • Herpesviridae• Herpesvirus• Human herpes

virus 1, HHV 2,HHV 3

  • Retroviridae• Lentivirus• Human

ImmunodeficiencyVirus 1, HIV 2

Provide an example of a family, genus, species, and acommon name of a virus.

Slide 13

Biol 240 S

13

Single Strand RNA Viruses

•^

Enveloped + strand

-^

Togaviridae–

Rubivirus – rubella

•^

Flavivirus–

Yellow fever

•^

Nonenveloped

-^

Picornaviridae–

Rhinovirus

-^

Common cold

-^

Poilovirus

•^

Calciciviridae–

Norovirus

-^

Stomach Flu

•^

Enveloped - strand

-^

Rhabdoviridae–

Rabies

•^

Filoviridae–

Ebola

•^

Orthomyxoviridae–

Influenza

-^

Multiple segments ofsingle stranded RNA

Provide examples of enveloped and non-enveloped RNAviruses Which enzyme do most RNA viruses carry with theminside their capsids, and why?

Explain the difference between +RNA and –RNA viruses

Slide 14

Biol 240 S

14

Culturing Viruses

•^

Viruses must begrown in living cells.

-^

Bacteria–

Phages

•^

Live animals

-^

Embryonated eggs–

Vaccine development

•^

Animal cell cultures

-^

vaccinations

List the different methods that can be used to growanimal viruses in a laboratory.

Slide 15

Biol 240 S

  • Cytopathic effects• Serological tests
    • Detect antibodies against viruses in a patient– Use antibodies to identify viruses in

neutralization tests,

  • viral hemagglutination– Western blot
    • Nucleic acids
      • PCR– RFLPs

Virus

Identification

Slide 18

Biol 240 S

18 Figure 13.10.

5

Capsid

Tail fibers

One Step Growth Curve

Slide 19

Biol 240 S

The Lysogenic Cycle

Figure 13.

Explain the basic difference between the lytic cycle ofphage multiplication and the lysogenic cycle. What is a prophage?

Slide 20

Biol 240 S

20

Specialized Transduction

Figure 13.

Prophage exists in galactose-using host(containing the

gal

gene).

Phage genome excises, carryingwith it the adjacent

gal

gene from

the host.Phage matures and cell lyses, releasingphage carrying

gal

gene.

1 2 3

Prophage

gal gal^ gene

gene

Bacterial DNA

Galactose-positivedonor cell

gal

gene

Phage infects a cell that cannot utilizegalactose (lacking

gal

gene).

4

Galactose-negativerecipient cell

Along with the prophage, the bacterial

gal

gene becomes integrated into the newhost’s DNA. 5

Lysogenic cell can now metabolizegalactose. 6

Galactose-positive recombinant cell

Describe a case where a bacterium owes its pathogenicityto specialized Transduction.

Slide 21

Biol 240 S

  • Attachment Viruses attaches to cell

membrane receptor

  • Penetration By endocytosis or fusion• Uncoating

By viral or host enzymes

  • BiosynthesisProduction of nucleic acid and

proteins

  • Maturation

Nucleic acid and capsidproteins

assemble

  • Release

Animal viruses By budding (envelopedviruses) or rupture

Describe how an animal virus like herpes simplex enteran animal cell?

Slide 24

Biol 240 S

24

Replication of DNA Virus

Figure 13.

Virion attaches to host cell

Virion penetratescell and its DNA isuncoated

Early transcription andtranslation; enzymes aresynthesized

1

2

3

DNA

Late transcription;DNA is replicated 4

Late translation;capsid proteinsare synthesized Virions mature 6 5

Capsid

Papovavirus

Host cell

DNA Cytoplasm

Virions are released 7

Capsid proteins

mRNA

Following uncoating, describe the biosynthesis of a DNAvirus.

Slide 25

Biol 240 S

+ RNA or SenseStrand = mRNA

•^

Viral genometranscribed

-^

“early proteins”–

Enzymes forviral replication

•^

RdRp–

Synthesizes –stand

-^

template formaking new +strands

•^

“late proteins”–

capsid proteins

Following uncoating, describe the biosynthesis of a+RNA virus.

Slide 26

Biol 240 S

26

- Strand RNA Viruses - RNA dependent

RNA Polymerase

  • Uses – strand to

make + strand

    • strand (mRNA)

transcribed intoviral proteins

Slide 27

Biol 240 S

Retrovirus Replication

Figure 13.

Retrovirus penetrateshost cell.

Virion penetratescell and its DNA isuncoated

The new viral DNA istranported into the host cell’snucleus and integrated as aprovirus. The provirus maydivide indefinitely with thehost cell DNA.

1

2

3

DNA

Transcription of theprovirus may also occur,producing RNA for newretrovirus genomes andRNA that codes for theretrovirus capsid andenvelope proteins. 4

Matureretrovirusleaves hostcell, acquiringan envelope asit buds out. 5

Capsid

Reversetranscriptase

Virus

Two identical + stands of RNADNA of one of the hostcell’s chromosomes

Provirus

Hostcell

Reversetranscriptase Viral RNA

RNA

Viral proteins

Identicalstrands ofRNA

How does the biosynthesis of the retroviridae differ fromthat of other viruses?

Slide 30

Biol 240 S

30

Latent v Persistent Infections

  • Latent Viral Infections
    • Virus remains in asymptomatic

host cell for long periods

  • Cold sores, shingles
    • Persistent Viral Infections
      • Disease processes occurs over a

long period, generally fatal

  • Subacute sclerosing panencephalitis

(measles virus)

What is a provirus? And provide an example of a latentviral infection.

Slide 31

Biol 240 S

Viral Therapy

•^

Pathogen specificbacteriophages

-^

Phages mutate at samerate as bacteria

-^

Selective

-^

Phages multiply insidepatient

-^

Viriotherapy

-^

Oncolytic virusesselectively bind to anddestroy cancer cells

Slide 32

Biol 240 S

32

  • Infectious proteins• Inherited and transmissible by ingestion,

transplant, & surgical instruments

  • All are fatal• Spongiform encephalopathies:• Sheep scrapie,• Creutzfeldt-Jakob disease• Mad cow disease

Prions

What are prions and how are they transmitted?

Slide 33

Biol 240 S Prions

Figure 13.

PrP

c

PrP

Sc

1

2

3

4

5

6

7

8

Endosome

Lysosome

Explain how prions cause diseases like BovineSpongiform Encephalopathy?

Slide 36

Biol 240 S

36

Vaccine History

• Variolation: Inoculation of smallpox

into skin (

th

century)

• Vaccination: Inoculation of cowpox

(Vaccina) into skin

Slide 37

Biol 240 S

Vaccination

  • Prevention better

(and cheaper)thancure

  • Herd Immunity• Epidemics• Eradication
    • Small pox– Polio?– Measles?

Why is it better to vaccinate against viral disease, likepolio, that someone may never have than to treat thesymptoms if the individual contracts a viral disease?

Following the eradication of smallpox, which viraldiseases are the likely targets for the next globaleradication efforts.

Slide 38

Biol 240 S

Attenuated Whole-Antigen

Vaccines

  • Living, but

weakened virus

  • Lifelong immunity• 95% effective• Living virus

replicates in body

  • Polio - Sabin

Compare the use of attenuated whole-agent vaccines toinactivated whole-agent vaccines in terms of theireffectiveness and safety.