CHAPTER 13: VIRUSES AND PRIONS

108. Describe the difference between acute, latent, and persistent viral infections. What is an example of each?

1) Acute infection: characterized by rapid onset of disease, a relatively brief period of symptoms, and resolution within days. It is usually accompanied by early production of infectious virions and elimination of infection by the host immune system. Ex. flu 2) Latent infection: remains asymptomatix jost cell for long periods, viruses not usually released - may reactivate due to changes in immunity Ex. cold sores: caused by the herpes virus Ex. shigles: caise by the varciella virus; also causes chickenpox 3)Persistent infection: occurs gradually over a long period; is generally fatal Ex. measles virus: ma remain hidden in the brain for many years and cause encephalitis (brain inflammation) Ex. Human papillomavirus: can lead cervical cancer

95. Describe the 6 steps in animal virus replication.

1) Adsorption (attachment): binding of virus to specific molecule on host cell 2) Penetration: genome enters host cell 3) Uncoating: the viral nucleic acid is released from the capsid 4) Synthesis: viral components are produced 5) Assembly: new viral particles are constructed 6) Release: assembled viruses are released by budding (exocytosis-leave w/some of the cell membrane) or cell lysis (cell bursts)

114. What are the 5 stages in the lytic cycle of bacteriophage multiplication? Describe each step.

1) Attachment: phage attaches by tail fibers to host cell 2) Penetration: phage lysozyme open cell wall; tail sheath contacts to force tail core and DNA into cell 3) Biosynthesis: production of phage DNA and RNA inside the bacteria 4) Maturation: assembly of phage particles into varions (complete infectious virus) 5) Release: phage lysozyme breaks cells wall and new formed viruses are released

104. How are viruses identified (3)? What is the MOST common way that viruses are identified?

1) Cytoplasmic effects 2) Serological test: ex. western blotting - rxn of the virus w/antibodies - most common 3) nucleic acids: a) RELPs - slight changes b) PCR amplification and detection of viral DNA

100. What are the two ways through which animal viruses penetrate the host cell?

1) Endocytosis: binds to cell membrane and virus will enter the cell via endocystosis (cell engulfs the virus). Then, the virus dissolves inside the cell. Ex. herpes virus 2) Fusion: virus binds to the cell membrane and receptors diffuse on it. After half of the receptor is diffuse with the cell membrane, the virus (naked) can enter the cell. E. mumps virus.

105. What are the 3 main categories for how antiviral drugs work (you do not need to know the examples given)?

1) Entry inhibitors inhibit: either attachment, fusion, uncloating - prevent virus from entering the cell 2) Nucleic acid synthesis inhibitors inhibit: viral polymerase, reverse tanscriptase, integrase 3) Assembly and release inhibitors inhibit: protease (enzyme required to clip viral proteins into functional pieces)

What are the 4 types of viral shape?

1) Helical 2) Polyhedral 3) Complex 4) Enveloped

102. What are 3 ways that animal viruses are grown in the lab?

1) In living animals 2) In embryonic eggs - virus injected in the egg - viral growth is signaled by changes or death of the embryo 3) In cell cultures - cells are treated with enzymes to separate cells - virally infected cells are detected via their deterioration (cytoplasmic effects) - continuous cell lines are used

93. What are the 4 enzymes that viruses can produce? Which enzyme do retroviruses use to direct the formation of DNA from RNA?

1) Polymerase: synthesize of DNA and RNA 2) Replicases: copy RNA (RNA > RNA) 3) Reverse transcriptase: synthesis of DNA from RNA (RNA > DNA). Known as retroviruses - used for viruses that RNA as their genetic information. Ex. HIV 4) Lysozyme: enzyme to degrade cell walls - found in bacteriophage (viruses that effect bacteria)

1)Helical 2) Polyhedral 3)Complex 4)Enveloped

1) The virus capsid shape that is a hollow cylinder with nucleic acid inside. Ex. Ebola or rabies 2) The virus capsid shape that is many sided; icosahedron. Ex. adehovirus - effects respiration system 3) Have both a helical and polyhedral shape. Ex. bacteriophage 4) Roughly spherical, but are polymorphic (many shapes). The capsid inside the envelope can either be helical or polyhedral. Ex. influenza virus.

85. What are viruses classified by? (3)

1) Type of nucleic acid - DNA or RNA (single or double stranded) 2) Morphology 3) Replication strategy (w/in the host cell)

107. What is required for a virus to multiply in a host cell? (2)

1) must invade the host cell 2) must take over the host's metabolic machinery

83. What are the 10 general characteristics of viruses?

1) not considered living 2) obligate intracellular parasites 3) ultra microscopic size 4) no cellular in nature (structure = compact and economical) 5) protein shell (capsid) 6) nucleic acid can either be DNA or RNA and can either be singled or double stranded 7) molecules on surface to attach to host cell 8) multiply by taking control of host cells genetic material and regulating the synthesis and assembly of new viruses 9) lack enzymes for metabolic processes 10) lack machinery for synthesizing protein

87. What are the two parts of the nucleocapsid?

1) nucleic acid (core) 2) (protein) capsid

89. What is a capsid and what is it made of?

All viruses have capsids - protein coats that enclose and protect their nucleic acid Constructed from identical repeatedly sub units called capsomers made of protein - some have an external covering (envelope) and some lack it (naked)

110. What do we call viruses that infect bacteria?

Bacteriophage

113. What is a plaque and what does each plaque correspond to?

Bacteriophage forms plaques - clearings on the surface of the agar one plaque = single virus (PFU-plaque forming unit)

99. How does virus adsorption occur for animal viruses? How is this different between enveloped and non-enveloped viruses?

Both: always occur via receptors; receptors are protein + sugar; and some type of attachment Enveloped: viruses uses spikes located on the envelope; Ex. influenza Non-enveloped (naked): the attachment sites are small fibers on the corners of the icosahedron; Ex. rhinovirus

101. Which term refers to the gradual release of viruses by an infected cell that is not immediately lysed? What term refers to when nonenveloped and complex viruses are released when the host cell dies and ruptures?

Budding: exocytosis (exiting the cell); nucleocapsid binds to membrane which pinches off to exit cell. Enveloped viruses will use this method. May not kill the cell. Lysis: cell bursting; and kills cells automatically.

90. What are the identical protein subunits called that make up a capsid called?

Capsomers.

88. What nucleic acid(s) are found in viruses? What are some of the possible structures of viral DNA (e.g single stranded, circular, etc.)? What types of genes are typically in a viral genome?

Either DNA or RNA (never both) - maybe segmented Single stranded, double stranded, linear or circular Carries genes necessary to invade host cell and redirect cell's activity to make new viruses. Number of genes varies for each type of virus - few to hundreds

86. Are antimicrobial drugs more likely to be effective towards naked or enveloped viruses? Why?

Enveloped viruses. Most sensitive to antimicrobial chemicals because most are lipid soluble (dissolves phospholipids) & viruses will no longer be able to attach to host.

92. What are the spikes used for on a viral envelope?

Essential for attachment of the virus to the host cell.

91. What is the viral envelope and what is it composed of? Where is the viral envelope, relative to the capsid (inside or outside?)? Are enveloped viruses monomorphic or pleomorphic? What advantage does the viral envelope give a virus?

F(x) = to hide from the hosts immune system A phospholipid layer; only in some viruses - usually in animal viruses Composed of host cell membrane (acquired when the virus leaves the host cell) surrounds the capsid Pleomorphic (many shapes) Exposed carbohydrate-protein complexes on the outside of the envelope called spikes

96. True or False. A specific animal virus has the ability to attach to and enter almost any animal host cell. Explain you answer.

False. Most viruses can only infect on host species. Determined by availability of appropriate attachments sites on surfaces of the host cell. Virus bind with receptors sites.

112. How are bacteriophage grown in the laboratory?

Grown in bacteria (living bacteria)

98. Does hepatitis B have a narrow or a broad host range? What type of cells can the hepatitis B virus infect? What about rabies?

Hepatitis B: narrow host range - only infect liver cells Rabies: broad host range - various cells of many mammals

118. What is the lysogenic cycle in bacteriophage? What happens during the lysogenic cycle?

Lysogeny: phage remains latent Phage DNA incorporated into host cell DNA -inserted phage DNA is known as prophage -when the cell replicates its chrromosomes, it replicates the prophage DNA also -results in phage conversion - the host cell exhibits new properties Also known as temperate phage (*Bacteria may acquire ability to produce toxins)

117. How are phage released from bacterial cells?

Occurs by lysis only. Enough viral particles in a bacteria can rupture the cell. **part of the lytic cycle

109. What do we call mammalian viruses capable of initiating tumors?

Oncoviruses (10% of cancers are known to be virally)

106. What are interferons used for?

Prevent spread of viruses to new cells. Produce naturally by virally infected cells. Magnifies an immune response. Inhibit viral replication and cancer cells. Drug Ex. Imiquimod: promotes interferon production.

119. What are prions, satellite viruses, and viriods?

Prions: proteinaceous infectious particles - misfolded proteins, contain no nucleic acid > causes transmissible spongiform encephalopathies (fatal neuro-degenerative diseases). Extremely resistant to usual sterilization techniques. Satellite viruses: dependent on other viruses for replication - adeno-associated virus: replicate only in cells infected with adenovirus - delta-agent: naked strand of RNA expressed only in the presence of hepatitis B virus Viriods: short pieces of RNA, no protein coat, only been identified in plants, so far

116. What enzyme do phage produce that allow them to break down bacterial cell walls so that they may inject their DNA into a host cell?

Produce lysozyme to degrade bacterial cell wall (*tail sheath contracts and driven down the cell wall an when the to reaches the plasma membrane - the phage DNA will pass from the capsid head > tail > plasma membrane > bacteria cell) **part of the lytic cycle

97. What is host range? What does host range depend on?

Spectrum of cells a virus can infect Limited by the receptors found on the host cell

115. Which structure on bacteriophage allow them to attach to host cell receptors?

The phage uses fibers at the end of the tail to attach to cell wall (part of the lytic cycle)

84. What is the term for the fully formed virus that is able to establish an infection?

Virion

103. What are cytopathic effects and what are the 7 examples of cytopathic effects?

-Virus induced damage to cells -Virally infected cells are detected via theri deterioration; also known as CPE. 1) changes in size and shape 2) cytoplasmic inclusion bodies (vesicles) 3) nuclear inclusion bodies 4) cells fuse to form multi-nucleated cells 5) cell lysis 6) alter DNA 7) transform cells into cancerous cells

111. What step happens in animal virus multiplication, but doesn't happen in bacteriophage multiplication?

-only nucliec acid enters the cytoplasm - uncouting is not necessary in bacteriophage because capsid doesn't enter the cell -releases only occurs via cell lysis only