1. Attachment: host specificity

- virus attaches to the animal cell

2. Penetration: virus enters the cell membrane

- "naked" virus = no membrane

- enter the eukaryotic cell by pinocytosis - active cellular process by w/c nutrients and other mol. are brought into a cell

- virus w/ memb. fused w/ cell memb.

- fusion in w/c the viral envelope fuses w/ the plasma memb. and releases the capsid into the cell's cytoplasm

- virus w/ memb. fused w/ cell memb. by phagocytosis

3. Uncoating: viral genetic material released fr. capsid; capsid is:

- digested in vesicles or released fr. vesicles

- digested in cytoplasm or

- digestion while still attached to cell memb.

4. Biosynthesis: 

- transcription of the DNA = produce mRNA

- replication of the viral DNA = some viral proteins are made

- translation = ribosomes use mRNA to make proteins

5. Assembly: proteins capsid is assembled

- release: when a portion of the plasma memb., now the envelope, adheres to the virus

- budding: when envelope develops around the capsid/viruses 

- proteins of virus

- membranes of host

- lysis: naked viruses

- DNA viruses

- ssRNA viruses

- (+) RNA

- (-) RNA

- dsRNA viruses

- retroviral viruses

ex: Papovavirus

ex: Herpesviridae, a DNA virus

1. attachment: virion attaches to host cell

2. penetration: virion enters cell and its DNA is uncoated

3. DNA is transcribed to make (+)RNA, mRNA that encodes "early" viral proteins

- host RNA polymerase (enzyme used to make RNA) for viral early mRNA synthesis or transcription

- proteins made here are enzymes to start viral DNA replication w/c are completed by host enzymes

4. viral DNA is replicated and some viral proteins are made

- late mRNA's made using host enzymes are exported to cytoplasm

- host enzymes make capsids & other viral proteins fr. late mRNA

5. late translation; capsid proteins are synthesized in the cytoplasm

-mRNA's encode capsids that are usually made by host enzymes

6. virions mature = migration of capsid proteins into nucleus

7. virions are released

ex: Picornaviridae such as poliovirus, it's called (+) strand b/c it can act as mRNA

ex: Flaviviridae

1. attachment to the host cell

2. penetration occurs: virus enters the cell, uncoats

- uncoating releases viral RNA and viral proteins

3. RNA replication by viral RNA-dependent RNA polymerase - an enzyme that catalyses the synthesis of another strand of RNA

- (+)RNA is transcribed/copied to make (-)RNA

- then (-)RNA acts as a template to produce additional (+)RNA

- (+)RNA serves as mRNA for:

- the translation of capsid proteins or

- may become incorporated into capsid proteins to form a new virus or

- may serve for continued RNA multiplication

4. translation and synthesis of viral proteins

- (+)RNA also serves as the viral RNA

5. maturation and release occurs

- once viral RNA and proteins are synthesized

ex: Rhabdoviridae such as rabiesvirus

ex: Orthomyxoviridae

- (-) ssRNA will not act as mRNA until it's been transcribed into the (+) ssRNA

1. attachment

2. penetration/uncoating

3. RNA replication by viral RNA-dependent RNA polymerase

- comes w/ virion & makes (+) strands

- (-)RNA is copied to make (+)RNA

- (+)RNA serves as a template to make (-)RNA

- (+)RNA serves as mRNA for the translation of capsid proteins

4. translation and synthesis of viral proteins

_{- (-)RNA serves as the viral RNA}

_{- (+)RNA also serves as a template for the synthesis of new viral RNA}

5. maturation occurs

- virions are then release fr. the host cells either by:

- budding or by rupturing the host cell plasma membrane

ex: Reoviridae, such as reoviruses

1. attachment

2. penetration

3. RNA replication by viral RNA-dependent RNA polymerase

- comes w/ virus

- strand forms mRNA (+RNA)

- mRNA is produced inside the capsid and released into the cytolasm of the host

4. translation and synthesis of viral proteins

- RNA polymerase initiates production of (-) strands

- mRNA and (-)strands form the dsRNA that is incorporated as new viral RNA

- capsid proteins and RNA-dependent RNA polymerase

- capsid & this enzyme are made fr. new mRNA

5. maturation and release: envelop

ex: Retroviridae, an RNA virus w/ reverse transcriptase

1. attachment

2. penetration/uncoating releases the RNA

3. biosynthesis:

- RNA is transcribed to make DNA

- DNA serves as a template to make (+)RNA

4. the new viral DNA is transported into the host cell's nucleus and integrated as a provirus

5. transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that encodes the retrovirus capsid, enzymes, and envelope proteins

- (+)RNA serves as mRNA for the translation of capsid protein

- (+)RNA serves as the viral genome

6. viral proteins are processed by viral protease; some of the viral proteins are moved to the host plasma memb. 

7. maturation takes place, and the mature retrovirus leaves the host cell

- mature retrovirus leaves the host cell, acquiring an envelope and attachment spikes as it buds out