Chapter 13: Viruses, Viroids, And Prions

Front 1

What are viruses? what do they contain?

Back 1

-Obligatory intracellular parasites
-replicate by assembly
-contain DNA or RNA (one or more segments)
-Some are enclosed by an envelope
-Some viruses have spikes or sophisticated structures

Front 2

Host range

Back 2

-is determined by specific recognitions between host receptors and viral proteins and by cellular factors affect viral replication and spread among cells *tissue and cell specificity: cellular surface receptors

Front 3

Virus sizes

Back 3

24nm-3000nm

Front 4

Viron structure

Back 4

-Nucleic acid (DNA or RNA)
-Capsid (capsomeres)
-Envelope
-Spikes

Front 5

3 types of viruses: Icosahedral virus, enveloped virus, and helical virus

Back 5

1) Icosahedral: 12 corners/ 20 sides/ 30 edges. Ex: Adenovirus
2) enveloped virus: Exs: Influenzavirus and Bovine Herpesvirus
3) Helical virus: long virus. Ex: Ebola virus

Front 6

Complex viruses:Bacteriophage. Components and example

Back 6

They have a capsid (head), DNA, Sheath, tall fiber(legs), Baseplate(bottom), and pin(injection). Ex: Human Smallpox virus- orthopoxvirus

Front 7

Taxonomy of Viruses

Back 7

-Order(-virales)
-Family names end in (-viridae)
-Genus names end in (-virus)
-Viral Species: Common English names (Tobacco mosaic virus, Human immunodeficiency virus)
-Subspecies are designated by a number or geographical origin

Front 8

Baltimore Classification Scheme: by Genome and Replication Strategies Part I: dsDNA viruses, ssDNA viruses, and dsRNA viruses

Back 8

-dsDNA viruses: replicate through dsDNA
-ssDNA viruses: replicate through dsDNA intermediates
-dsRNA viruses

Front 9

Baltimore Classification Scheme: by Genome and Replication Strategies Part II: ssRNA viruses, ssRNA viruses, and Ambisense ssRNA viruses

Back 9

-ssRNA viruses: (+)-sense genomes
-ssRNA viruses: (-)-sense genomes
-Ambisense ssRNA viruses: mosaics of +/- genomes

Front 10

Baltimore Classification Scheme: by Genome and Replication Strategies Part III: Retroviruses and Pararetroviruses

Back 10

-Retroviruses: diploid ssRNA viruses replication via dsDNA
-Pararetroviruses: dsDNA viruses replication via ssRNA

Front 11

Viral Infection Process: Entry

Back 11

STEP 1. Entry: dependent on all cell wall types.
-Animals: attachment to cell membrane, endocytosis, or fusion
-Plants: wounds, insects
-Bacteria: attachment to cell wall receptors or pili, injected or pulled into cells

Front 12

Viral Infection Process: Uncoating

Back 12

STEP 2. Uncoating: removal of capsid to exposed nucleic acids

Front 13

Viral Infection Process: Biosynthesis: Gene expression/transcription

Back 13

STEP 3. Biosynthesis: Production of proteins and nucleic acids
-Gene expression (1st step for positive RNA viruses)
-Transcription (1st step for DNA viruses and negative RNA viruses)

Front 14

Viral Infection Process: Assembly

Back 14

STEP 4. Assembly: Nucleic acid and capsid proteins form virions

Front 15

Viral Infection Process: Release

Back 15

STEP 5. Release: by budding (enveloped viruses) or rupture or spreading to neighboring cells through plasmodesmata (plants)

Front 16

Attachment, penetration, uncoating

Back 16

By pinocytosis or by membrane fusion. (see slide for examples of both)

Front 17

dsDNA Viruses

Back 17

1) dsDNA genome enters into the nucleus
2) transcription of genes usually by host RNA polymerase
3) Semi-conservative replication of viral genomes by either host or viral DNA polymerase

Front 18

ds DNA: Replication of DNA Virus steps 1-7

Back 18

1) Virion attaches to host cell
2) Virion enters cell, and its DNA is uncoated
3) A portion of viral DNA is transcribed, producing mRNA that encodes "early" viral proteins
4) Viral DNA is replicated and some viral proteins are made
5) Late translation: capsid proteins are synthesized.
6) Virions mature
7)Virions released

Front 19

ssDNA Viruses

Back 19

-ssDNA first converted to dsRNA by host DNA polymerase
-Genes are expressed
-A viral protein (Rep) initiate a rolling circle replication of the viral genome by a host DNA polymerase

Front 20

dsRNA viruses

Back 20

-Carry a transcriptase (RNA-dependent RNA polymerase) in virions
-mRNA transcribes within the virion and then extruded for translation
-Once all proteins and progeny viral RNA are made, and immature virion is formed, within which ssRNA is converted to dsRNA

Front 21

dsRNA viruses replication steps 1-5

Back 21

1) attachment
2) Entry and uncoating
3) DNA replication by viral RNA-dependent RNA polymerase
4)Translation and synthesis of viral proteins
5)Maturation and release

Front 22

(+) ssRNA Viruses

Back 22

-Genomic RNA is the same sense (+ sense) as mRNA, therefore translated DIRECTLY
-RdRp translated from genomic RNA
-(+)-sense RNA copied to (-)-sense RNA (complementary RNA)
-(-)-sense RNA serves as template to produce (+)-sense, genomic RNA

Front 23

(+) ssRNA Virus replication steps 1-5

Back 23

1) Attachment
2) Entry and uncoating
3) RNA replication by viral RNA-dependent RNA polymerase
4) Translation and synthesis of viral proteins
5) Maturation and release

Front 24

(-) strand and ambisense RNA viruses

Back 24

- (-)sense RNA viruses have a genome that is complementary to mRNA
-Ambisense RNA viruses have a mosaic genome of partial (+) or partial (-) sense RNA (ambiguous senses)
-Viral genomic RNA cannot serve as messenger RNA, a virus must carry a transcritpase
-Influenze viruses, Ebola virus, Hantavirus, Tomato spotted wilt virus

Front 25

(-) Strand RNA virus Steps 1-5

Back 25

1) Attachment
2) Entry and uncoating
3) RNA replication by viral RNA-dependent RNA polymerase
4) Translation and synthesis of viral proteins
5) Maturation and release

Front 26

Orthomyxoviridae

Back 26

Influenza A- Causes "epidemic influenza"
-An enveloped segmented (-) ssRNA virus
-In nature, Influenze is a wild bird virus
-There are human adapted strains but also, equine, swine, domestic bird(chicken) Flu strains
-Influenze mutates rapidly, recombines frequently and sometimes jumps species

Front 27

Retroviruses

Back 27

-Virions contain a "diploid" ssRNA genome
-Carry a reverse transcriptase
-Upon infection, ssRNA is reverse-transcribes into dsDNA in cytoplasm
-dsDNA transported into nucleus and integrated into host genome
-Progeny viral RNA transcribes from the integrated provirus sequence
-HIV, Human T-cell leukemia viruses