chapter 13
Download
Skip this Video
Download Presentation
Chapter 13

Loading in 2 Seconds...

play fullscreen
1 / 47

Chapter 13 - PowerPoint PPT Presentation


  • 49 Views
  • 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

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

slide2
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
slide3
Felix d’Herelle, 1917
    • Bacteriophage
    • Suggested phage therapy
  • 1930’s, term virus introduced and electron microscopy invented
  • Wendell Stanley, 1935
    • Isolated tobacco mosaic virus
slide5
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
slide6
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
slide9
3 primary means of classification:

Nucleic acid

Replication strategy

Morphology of protein coat (capsid)

helical viruses
Helical Viruses

Polyhedral Viruses

slide11
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
slide19
Animal & plants viruses may be grown in cell cultures
    • Primary cell lines
    • Continuous cell lines (transformed cells )
virus identification
Virus Identification
  • 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

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

Multiplication of Bacteriophages
lytic cycle
Lytic Cycle
  • 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
slide26
3 Important results of lysogeny
    • Immunity to re-infection
    • Phage conversion
    • Specialized transduction
specialized transduction
Specialized Transduction

gal gene

Bacterial DNA

Prophage

1

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

Galactose-positive donor cell

gal gene

2

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

3

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

gal gene

4

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

Galactose-negative recipient cell

5

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

6

Lysogenic cell can now metabolize galactose.

Galactose-positive recombinant cell

multiplication of animal viruses
Multiplication of Animal viruses
  • 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
slide29
Attachment of animal viruses
    • Chemical attraction
    • No tails or tail fibers
    • Glycoprotein spikes or other attachment molecules
slide30
Replication of Animal Viruses
    • 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

Papovavirus

1

Virion attaches to host cell

7

Virions are released

Host cell

DNA

Capsid

2

DNA

Virion penetrates cell and its DNA is uncoated

Cytoplasm

6

Virions mature

Capsid proteins

mRNA

5

Late translation; capsid proteins are synthesized

3

Viral DNA penetrates host nucleus

Early transcription and translation; enzymes are synthesized

4

Late transcription; DNA is replicated

multiplication of rna virus
Multiplication of RNA Virus

[INSERT FIGURE 13.13]

multiplication of a retrovirus
Multiplication of a Retrovirus

Capsid

Reverse transcriptase

DNA

Virus

Two identical + stands of RNA

1

Retrovirus penetrates host cell.

Host cell

DNA of one of the host cell’s chromosomes

5

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

Reverse transcriptase

2

Virion penetrates cell and its DNA is uncoated

Viral RNA

Identical strands of RNA

4

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

RNA

3

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.

Provirus

slide35
Assembly and release of animal viruses
      • 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
  • 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
slide39

Oncoviruses

    • Viral DNA integrated into host DNA
    • Induces tumors
oncogenic viruses
Oncogenic Viruses
  • Oncogenic DNA Viruses
    • Adenoviridae
    • Herpesviridae
    • Poxviridae
    • Papovaviridae
    • Hepadnaviridae
  • Oncogenic RNA viruses
    • Retroviridae
      • DNA
      • HTLV 1
      • HTLV 2
slide41
Latent Viral Infections
    • 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)
slide43

Plant Viruses

    • Plant viruses enter through wounds or via biting insects
    • May be transmitted in pollen
  • Viroids
    • infectious naked RNA

Potato Spindle Tuber Viroid

prions
Prions
  • Proteinaceous infectious particle
  • Inherited and transmissible diseases
  • Spongiform encephalopathies
    • Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease
slide47

[INSERT FIGURE 13.23]

scrapie proteinsaccumulate in brain cells forming large vacuoles

ad