Chapter 13
1 / 47

Chapter 13 - PowerPoint PPT Presentation

  • Uploaded on

Chapter 13. Viruses, Viroids and Prions. Adolf Mayer, 1886 tobacco mosaic disease (TMD) transmissible Dimitri Iwanowski, 1892 Filtered sap still caused TMD contagious fluid or filterable agent Walter Reed,1901 Yellow Fever. Felix d’Herelle, 1917 Bacteriophage Suggested phage therapy

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' Chapter 13' - bradley-barrera

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Chapter 13

Chapter 13

Viruses, Viroids and Prions

Chapter 13

  • Adolf Mayer, 1886

    • tobacco mosaic disease (TMD) transmissible

  • Dimitri Iwanowski, 1892

    • Filtered sap still caused TMD

    • contagious fluid or filterable agent

  • Walter Reed,1901

    • Yellow Fever

Chapter 13

  • Felix d’Herelle, 1917

    • Bacteriophage

    • Suggested phage therapy

  • 1930’s, term virus introduced and electron microscopy invented

  • Wendell Stanley, 1935

    • Isolated tobacco mosaic virus

Chapter 13

  • Viral Features

    • Obligate intracellular pathogen

    • Host range

      • highly specific or generalists

    • DNA or RNA

    • Protein coat

    • Surface proteins highly susceptible to mutations

    • Cause synthesis of specialized structures to transfer viral particles to other cells

Chapter 13

  • Virion

    • complete, fully developed, infectious viral particle

    • Living or non-living entities?????

Viral classification
Viral Classification

  • Oldest system based on symptomology

  • International Committee on Taxonomy of Viruses (ICTV), 1966

    • Describe viruses as elementary bio-systems

    • Classified into orders, families, genera and species

    • Over 1,500 officially recognized species

Chapter 13

3 primary means of classification:

Nucleic acid

Replication strategy

Morphology of protein coat (capsid)

Helical viruses
Helical Viruses

Polyhedral Viruses

Chapter 13

  • Viral Envelope

    • Acquired from host cell

    • Phospholipids and proteins

    • Some glycoproteins are virally coded spikes

    • Often play role in host recognition

Viral taxonomy
Viral Taxonomy

  • Order –virales

  • Family –viridae

  • Genus – virus

  • Species

    • Common names

    • Subspecies designated by a number

Viral taxonomy1
Viral Taxonomy

  • Retroviridae– family

    • Lentivirus – genus

      • Human Immunodeficiency Virus– species

  • Herpesviridae

    • Simplexvirus

      • Human herpesvirus 1, HHV 2, HHV 3

Isolation and cultivation of viruses
Isolation and Cultivation of Viruses

  • Viruses must be grown in living cells

    • Cytopathic effects

Chapter 13

Virus identification
Virus Identification embryonated eggs

  • Serological tests

    • Detect antibodies against viruses in a patient

  • Nucleic acids

    • RFLPs

    • PCR

Multiplication of bacteriophages

Lytic cycle Phage causes lysis and death of host cell embryonated eggs

Lysogenic cycle Temperate phages incorporate DNA into host DNA (prophage)

Multiplication of Bacteriophages

Lytic cycle
Lytic Cycle embryonated eggs

  • Attachment Phage attaches by tail fibers to host cell

  • Penetration Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell

  • Biosynthesis Production of phage DNA and proteins

  • Maturation Assembly of newly synthesized phage particles

  • Release Phage lysozyme breaks cell wall

Chapter 13

[INSERT FIGURE 13.8] embryonated eggs

One step growth curve
One-step Growth Curve embryonated eggs

Lysogenic cycle
Lysogenic Cycle embryonated eggs

Chapter 13

Specialized transduction
Specialized Transduction embryonated eggs

gal gene

Bacterial DNA



Prophage exists in galactose-using host (containing the gal gene).

Galactose-positive donor cell

gal gene


Phage genome excises, carrying with it the adjacent gal gene from the host.


Phage matures and cell lyses, releasing phage carrying gal gene.

gal gene


Phage infects a cell that cannot utilize galactose (lacking gal gene).

Galactose-negative recipient cell


Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA.


Lysogenic cell can now metabolize galactose.

Galactose-positive recombinant cell

Multiplication of animal viruses
Multiplication of Animal viruses embryonated eggs

  • Attachment Viruses attaches to cell membrane

  • Penetration By endocytosis or fusion

  • Uncoating By viral or host enzymes

  • Biosynthesis Production of nucleic acid and proteins

  • Maturation Nucleic acid and capsid proteins assemble

  • Release By budding (enveloped viruses) or rupture

Chapter 13

  • Attachment of animal viruses embryonated eggs

    • Chemical attraction

    • No tails or tail fibers

    • Glycoprotein spikes or other attachment molecules

Chapter 13

  • Replication of Animal Viruses embryonated eggs

    • Biosynthesis

      • Each virus requires different strategy depending on its nucleic acid

      • DNA viruses often enter the nucleus

      • RNA viruses typically replicate in cytoplasm

      • Must consider:

        • What serves as template for replication and how mRNA is transcribed

Multiplication of dna virus
Multiplication of DNA Virus embryonated eggs



Virion attaches to host cell


Virions are released

Host cell





Virion penetrates cell and its DNA is uncoated



Virions mature

Capsid proteins



Late translation; capsid proteins are synthesized


Viral DNA penetrates host nucleus

Early transcription and translation; enzymes are synthesized


Late transcription; DNA is replicated

Multiplication of rna virus
Multiplication of RNA Virus embryonated eggs


Multiplication of a retrovirus
Multiplication of a Retrovirus embryonated eggs


Reverse transcriptase



Two identical + stands of RNA


Retrovirus penetrates host cell.

Host cell

DNA of one of the host cell’s chromosomes


Mature retrovirus leaves host cell, acquiring an envelope as it buds out.

Reverse transcriptase


Virion penetrates cell and its DNA is uncoated

Viral RNA

Identical strands of RNA


Transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that codes for the retrovirus capsid and envelope proteins.

Viral proteins



The new viral DNA is tranported into the host cell’s nucleus and integrated as a provirus. The provirus may divide indefinitely with the host cell DNA.


Chapter 13

  • Assembly and release of animal viruses embryonated eggs

    • Most DNA viruses assemble in and are released from nucleus into cytosol

    • Most RNA viruses develop solely in cytoplasm

    • Enveloped viruses cause persistent infections

    • Naked viruses are released by exocytosis or may cause lysis and death of host cell

Viruses and cancer
Viruses and Cancer embryonated eggs

  • Oncogenes transform normal cells into tumor cells

    • Activated by mutagenic chemicals, radiation, viruses

    • Causes increased growth, loss of contact inhibition

    • Cells tend to be misshapen and exhibit chromosomal abnormalities

Chapter 13

  • Oncoviruses embryonated eggs

    • Viral DNA integrated into host DNA

    • Induces tumors

Oncogenic viruses
Oncogenic Viruses embryonated eggs

  • Oncogenic DNA Viruses

    • Adenoviridae

    • Herpesviridae

    • Poxviridae

    • Papovaviridae

    • Hepadnaviridae

  • Oncogenic RNA viruses

    • Retroviridae

      • DNA

      • HTLV 1

      • HTLV 2

Chapter 13

  • Latent Viral Infections embryonated eggs

    • Virus remains dormant in asymptomatic host cell for long periods

      • Cold sores, shingles

  • Persistent Viral Infections

    • Disease progresses slowly over a long period, generally fatal

      • Subacute sclerosing panencephalitis (measles virus)

Chapter 13

  • Plant Viruses embryonated eggs

    • Plant viruses enter through wounds or via biting insects

    • May be transmitted in pollen

  • Viroids

    • infectious naked RNA

Potato Spindle Tuber Viroid

Prions embryonated eggs

  • Proteinaceous infectious particle

  • Inherited and transmissible diseases

  • Spongiform encephalopathies

    • Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease

Prp c normal cellular prion protein prp sc scrapie protein
PrP embryonated eggsC, normal cellular prion proteinPrPSc, scrapie protein

Chapter 13

[INSERT FIGURE 13.23] embryonated eggs

scrapie proteinsaccumulate in brain cells forming large vacuoles