Chapter 6 Review

• - Naked nucleocapsid virus
• - nucleicacid
• - capsid

• - Envelope Virus
• - nucleic acid
• -capsid
• -envelope
• -spikes

- unique group of biological entities known to infect every type of cell

• - unusual structure and behavior
• - all possess a protein capsid surrounding some type of nucleic acid

- infectious particles

- obligate intracelluar parasites

• - protective outer shell that surrounds viral nucleic acid
• - capsid spikes are used for attachement to host cells
• - composed of capsomer subunits
• - two types of capsids
• - helical
• - icosahedral

• - rod-shaped capsomers bond forming a hollow disc similar to a bracelet
• - form a continuous helix
• - nucleic acid coils inside

• - naked helical virus
• - tobacco virus
• - nucleocapsid is rigid and tightly wound into a cylinder-shaped package

• - Enveloped helical virus
• - influenza, measles, rabies
• - nucleocapsid is more flexible
• - envelope comes from host cell membrane

- three dimensional, 20 sided with 12 evenly spaced corners

• - variation in capsomer numbers
• - polio virus 32 capsomers
• - adenovirus 240 capsomers

• - naked icosahedral viruses
• - papillomavirus

• - Enveloped icosahedral viruses
• - herpesvirus
• - envelope comes from host cell membrane

• - most common among animal viruses
• - lipid and proteins
• - during release of animal viruses, a part of the host membrane is taken

• - has envelope spikes for attachment of viruses to the next host cell
• - enable pleomorphic shape of the viruses

- protect nucleic acid from the host's acid and protein digesting enzymes

- assist in binding and penetrating host cell

- stimulate the host's immune system

• - intricate structure
• - pox virus
• - several layers of lipoproteins
• - course surface fibrils

• - bacteriophage
• - polydedral head
• - helical tail
• - fibers for attachment

- viruses contain either DNA or RNA but not both

- possess only the genes to invade and regulate the metabolic activity of host cells

- no viral metabolic genes; the virus uses the host's metabolic resources

• DNA viruses:
• - Enveloped
• - double stranded genome

• - Non-enveloped
• - single stranded genome
• - double stranded genome

• RNA Viruses:
• - enveloped - non-enveloped
• - single stranded genome - single stranded genome
• - segmented genome - double stranded genome
• - non segmented genome

• - adsorption (attachment)
• - penetration/uncoating
• - synthesis
• - assembly
• - release

• - viral attachment to host cell is mediated by spike proteins
• - spikes recognize only certain host receptors
• - basis for specificity

• - naked viruses are endocytosed
• - requires degradation of cell membrane and capsid prior to uncoating

• -enveloped viruses
• - viral envelope fuses to host cell membrane
• - allows only capsid to directly enter cytosol

• - liberated by budding or exocytosis
• - allows them to retain a portion of the host cell membrane

• - Damage to the host cell due to a viral infection
• - inclusion bodies: compact masses of viruses of damaged cellular material
• - syncytia: fusion of multiple host cells into a single, large, multinucleated cell
• - chronic latent state: viruses remain dormant in a certain cell type periodically becoming reactivated
• - transformation: viral geneic material permanently alter host genome
• - oncogenes

• - virus that specifically infects bacteria
• - multiplication is similar to animal viruses except:
• - pentration occurs via injecting DNA
• - can form a dormant prophage (lysongeny)
• - release (lyses) destroys the cell

- viral enzymes weaken host cell membrane

- leads to rupture the cell (lyses)

- release numerous virions

- insertion of viral DNA into the bacterial host genome

- allows viral DNA to be copied with every cell division of bacteria

- eggs provide an intact, self-supporting unit for viral maintenance

- viruses can be injected through shell into various areas within embryonic egg

• - tissues are grown on culture media
• - normal cells form an even monolayer of undisturbed cells

- viruses cause an aggregation of cells forming visible plaques

- prions

- satellite viruses

- viroids

- protein particle with no nucleic acid, no envelope, no capsid

• - Diseases
• - creutzfeldt- Jakob
• - "mad cow disease"

• - dependent on other viruses for replication
• - delta agent: naked RNA only expressed in the presence of hepatitis B virus potentially worsening the damage to liver cells

• - plant pathogens
• - tomatoes, potatoes, cucumbers

- 1/10th the size of normal viruses

- naked strands of RNA, no capsid