Chapter 6

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6 unique characteristics of viruses

1) have DNA or RNA, never both 2) tiny infectious particles, not cells 3) do not independently fulfill characteristics of life 4) multiply by taking control of host cell genetic material 5) lack enzymes for most metabolic processes 6) lack machinery for synthesizing protein

Cytopathic effects of viral infection include:

1) inclusions in the cytoplasm & nucleus 2) multinucleated giant cells 3) syncytia formation 4) cells round up

Viruses are used to produce vaccines for certain viral infections. T / F

True

Viruses cannot multiply outside a host cell. T / F

True

The nucleic acid of animal viruses enter the host cell through a. endocytosis b. fusion c. both a and b d. none of the above

c. both a and b

Enveloped viruses are released by a. endocytosis b. lysis of the host cell c. exocytosis d. fusion

c. exocytosis

A virus is a tiny infectious a. cell b. prokaryote c. particle d. nucleic acid

c. particle

Lysogeny refers to: a. altering the host range of a virus b. latent stage of herpes infection c. viral genome inserting into bacterial chromosome d. none of the above

c. viral genome inserting into bacterial chromosome

Plants are affected by virus like agents called a. virion b. satellite virus c. viroids d. prion

c. viroids

The nucleic acid of a virus is a. DNA only b. RNA only c. Both DNA and RNA d. Either DNA or RNA

d. Either DNA or RNA

Viral spikes: a. are always present on the viral envelop b. allow bacteria to evade host defense c. are derived from host proteins d. bind viral capsid and envelop together

d. bind viral capsid and envelop together

Classification of viruses involve all of the following except a. type of nucleic acid b. type of capsid c. presence of an envelop d. biochemical reactions

d. biochemical reactions

Viruses can not be cultivated in a. tissue culture b. bird embryos c. live mammals d. blood agar

d. blood agar

Helical and icosahedral are terms used to describe viral a. spike b. capsomer c. envelop d. capsid

d. capsid

The viral capsid is composed of protein subunits called a. spikes b. protomers c. virions d. capsomer

d. capsomer

Match A with B: A B 1) Lysogenic conversion a) Icosahedron 2) Enveloped virus b) Spongiform encephalopathy 3) Capsids c) Plant virus 4) Viroids d) Corynbacterium diphtheriae 5) Prions e) Exocytosis

1) D 2) E 3) A 4) C 5) B

Compare steps of viral multiplication cycles of bacteriophages and animal viruses

Bacteriophages -adsorption: Tail fibers attach to cell well of host -penetration: Injection of nucleic acid through cell wall, no uncoating -Synthesis: in cytoplasm -Persistence: lysogeny -Release: cell lyses when enzyme weaken Animal Virus -adsorption: attachment of capsid/envelope to cell surface receptors -Penetration: whole virus engulfed & uncoated or viral surface fuses with cell membrane, nucleic acid release -Persistence: latency, chronic infection, cancer -Release: lyses or exocytosis

A specific animal virus has the ability to attach to and enter almost any animal host cell. T / F

False

Adeno-associated virus and Delta agents are prions. T / F

False

Bacteriophages do not undergo adsorption to specific host cell receptors prior to penetration. T / F

False

Viruses are ultramicroscopic because they range in size from 2-450 um T / F

False

What dictates host range of animal virus? 2 ways animal viruses penetrate and leave host cell.

Host range dictated by receptor ligand specificity, cells that lack compatible receptors are resistant to adsorption/invasion by that virus. Animal viruses penetrate via fusion to membrane of host cell or endocytosis and exit via lyses or exocytosis.

Compare lysogeny and latency

Lysogeny- host chromosome carries bacteriophage DNA, infected host cell grow + reproduce for generations until they lyse. Prophage stays dorment in host until spontaneous lyses of cell releases prophage. Latency- viruses remain dorment in cells, sometimes year without activity, remain with the host cell and never released.

Prophages can be activated into viral replication and enter the lytic cycle. T / F

True

Compace virus, piron, and viroids

Virus- infectious particles, nucleic acid + capsid, sometimes envelope, causes many diseases. Prions- infectious proteins, no nucleic acid, no capsid, no envelope, cause spongiform encephalopathy in humans. Viroids- plant pathogen, no capsid, naked RNA strand, very small pathogens for important plants like tomato, cucumber, potatoes.

A prophage is an early stage in the development of a/an a. bacterial virus b. poxvirus c. lytic virus d. enveloped virus

a. bacterial virus

Infectious protein particles are called: a. prion b. viroids c. phages d. spikes

a. prion

In general, RNA viruses multiply in the cell-------, and DNA viruses multiply in the cell--------. a. nucleus, cytoplasm b. cytoplasm, nucleus c. vesicles, ribosome d. endoplasmic reticulum, nucleolus

b. cytoplasm, nucleus

Satellite viruses are a. also called viroids b. dependent on other viruses for replication c. the cause of spongiform encephalitis d. none of the above

b. dependent on other viruses for replication

T-even phages a. include the pox viruses b. infect the E.coli cells c. have helical capsids d. all of the above

b. infect the E.coli cells

An event that occurs in bacteriophage multiplication that does not occur during the multiplication of animal viruses is: a. adsorption to the host cell b. injection of viral nucleic acid into the host cell c. host cell synthesis of viral enzymes and proteins d. assembly of nucleocapsid

b. injection of viral nucleic acid into the host cell

Oncogenic viruses include all of the following except a. hepatitis B virus b. measles virus c. Epstein-Barr virus d. Papilloma virus

b. measles virus

The envelop of an animal virus is derived from the host cell' a. wall b. membrane c. glycocalyx d. receptors

b. membrane

Viruses have all of the following except a. genes b. metabolism c. definite shape d. ultramicroscopic size

b. metabolism

Clear patches in cell cultures that indicate sites of viral infection are called a. pocks b. plaques c. colonies d. prions

b. plaques

Enveloped viruses carry surface receptors called a. buds b. spikes c. fibers d. sheaths

b. spikes

These structures are used by bacteriophages to attach to host cell receptors a. sheath b. tail fibers c. nucleic acid d. none of the above

b. tail fibers

Host range is limited by: a. type of nucleic acid in the virus b. type of host cell receptors on the cell membrane c. age of the host cell d. size of the host cell

b. type of host cell receptors on the cell membrane

Infectious naked strands of RNA are called a. prions b. viroids c. spikes d. oncogenic viruses

b. viroids


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