Viruses

what are the mechanisms by which cancer is caused by a virus?

- The virus carries the genes that can cause cancer - Viral proteins cause changes in growth regulation, leading to cancer

Classifying viruses into families is based on

- structure - chemical composition - similarities in genetic makeup

What is the correct order of the viral life cycle phases?

1. Adsorption 2. Penetration & uncoating 3. Synthesis 4. Assembly 5. Release

MC A prophage is A. phage DNA integrated into host cell genome. B. phage DNA being actively expressed. C. phage protein left outside the bacterium. D. toxic to the host bacterial cell.

A. phage DNA integrated into host cell genome.

MC Which of the following terms is used to describe a viral RNA genome which cannot be immediately translated into protein? A. negative-sense B. transcription C. positive-sense D. neutral

A. negative-sense

Adsorption

Attachment of virus to new host cell via specific binding of its spikes to cell receptors - proteins (spikes) from the virus interact with host cell membrane receptors

MC Which of the following can cause a phage in the lysogenic stage to revert to the lytic stage? A. lack of nutrients B. Ultraviolet light C. A competing phage D. Darkness E. An electrical charge

B. Ultraviolet light

Non cellular infectious agents A. Bacteria B. Prions C. Satellite viruses D. Protozoa E. Viroids

B. C. E. Prions Satellite viruses Viroids

MC The negative (-) sense strand of RNA A. plays no role. B. makes RNA replicase. C. is used to synthesize more + strands. D. acts as mRNA to make viral proteins.

C. is used to synthesize more + strands.

MC In the release process, the viral capsid A. engulfs the viral spikes. B. surrounds the viral matrix protein. C. becomes completely enclosed by the region of the cell membrane into which the spikes and matrix protein are embedded. D. is dissolved.

C. becomes completely enclosed by the region of the cell membrane into which the spikes and matrix protein are embedded.

MC A positive (+) strand of RNA A. can not function directly as mRNA. B. makes a minus (-) strand of RNA which can then act as mRNA. C. can directly act as mRNA. D. must be double stranded.

C. can directly act as mRNA.

MC An envelope is acquired during which step of the viral life cycle? A. Penetration B. Synthesis C. Release D. Adsorption

C. Release An envelope is acquired during release through the host cell's plasma membrane.

MC plaques are associate with: A. rat flee transmission of viruses B. Viral infection of embryonated eggs C. bacteriophage infection of bacteria

C. bacteriophage infection of bacteria

In viral entry by endocytosis: A. the host cell's plasma membrane surrounds only the viral nucleic acid coat and forms a vesicle. B. viral spikes fuse with the host cell's plasma membrane to form a vesicle. C. the host cell's plasma membrane surrounds the whole virion and forms a vesicle. D. the host cell's plasma membrane surrounds only the viral protein coat and forms a vesicle.

C. the host cell's plasma membrane surrounds the whole virion and forms a vesicle.

MC A positive-sense RNA genome is ready for immediate A. replication to negative-sense RNA B. replication to DNA C. translation to protein D. reverse transcription to DNA

C. translation to protein

MC During replication of the positive (+) sense strand of lytic RNA phage, in order to make more positive (+) strands, A. the (+) RNA strand must code for the synthesis of RNA polymerase (replicase). B. the RNA replicase uses the (+) sense RNA as a template to make (-) strand RNA. C. the (-) sense strand RNA is used to make more (+) strands. D. All of the choices are correct.

D. All of the choices are correct.

MC In the lytic cycle of phage replication: A. phage genes integrate into the host cell genome and are not expressed. B. phage genes exist as prophage. C. phage DNA remains inside the protein coat. D. phage nucleic acid is replicated and phage genes are expressed, making new phage protein and lysing the host cell.

D. phage nucleic acid is replicated and phage genes are expressed, making new phage protein and lysing the host cell.

MC The first event to occur in the release of an enveloped virus is the A. inside of the host cell membrane becomes coated with viral matrix protein. B. viral capsid becomes enclosed by cell membrane. C. inside of host cell membrane becomes coated with capsid. D. viral spike proteins are inserted into host cell membrane.

D. viral spike proteins are inserted into host cell membrane.

MC The process by which bacteriophages infect bacteria conferring new traits enhancing human disease, is called: A. latency B. exocytosis C. lysogeny D. lysogenic conversion

D. Lysogenic conversion

MC Most bacteriophages contain which type of nucleic acid? A. ssRNA B. ssDNA C. dsRNA D. dsDNA

D. dsDNA

T/F In the lysogenic stage of phage replication, the host cell is lysed.

FALSE

T/F Once a phage becomes lysogenic, it will remain lysogenic and never be lytic again.

FALSE

True/False Animal viruses always kill cells they infect.

FALSE Some viruses do not kill their host cell, but instead remain latent inside of the cell.

True/False Viruses can be grown on culture media like bacteria.

FALSE Viruses can only be grown in living cells, because they require a host cell for metabolism and reproduction.

T/F A positive sense strand lytic RNA phage attaches to the cell wall of an E. coli bacterium.

FALSE it attaches to the pilus

True/False All viruses leave a cell by exocytosis.

False Some viruses are released when the cell lyses.

True/False A naked virus fuses with the host cell membrane.

False: Since a naked virus lacks an envelope, it cannot fuse with the plasma membrane. The envelope in enveloped viruses can fuse with the host cell's membrane allowing the nucleocapsid to enter the cell.

Release

Final stage of viral replication, culminating in complete virus or virion ready to infect another cell Can occur in 2 ways: 1. budding/exocytosis (enveloped viruses) 2. Lysis (bacteriophages & naked viruses)

Assembly

Host cell membrane proteins are used to create a new viral envelope structure - Viral spike proteins are inserted into the cell membrane for the viral envelope - nucleocapsid is formed from RNA and capsomers

Penetration & Uncoating

Receptor mediated endocytosis: 1. nucleic acid from capsid injected into host (bacteriophages) 2. Viral envelope fusion with cell membrane 3. Endocytosis of virus by cell Uncoating: - animal viruses use enzymes to dissolve the envelope (if present) & capsid in order to release the viral nucleic acid (RNA) into host cytoplasm

Synthesis

Replication and Protein production - virus hijacks host metabolic & replication machinery to create necessary components for assemblage of new virions - RNA molecules - capsomers - spikes

A portion of the viral envelope comes from the cell membrane of the host cell.

TRUE

T/F Both naked and complex viruses are released from host cells via lysis once mature.

TRUE

T/F Phage-induced lysozyme lyses the host cell releasing the newly made phage.

TRUE

true/false: Almost immediately upon entry, the viral nucleic acid alters the genetic expression of the host cell.

True The viral nucleic acid alters the genetic expression of the host cell soon after infection.

True/False Both enveloped and naked viruses can enter a cell by endocytosis.

True. Both enveloped and naked viruses can enter a cell by endocytosis.

Temperate phage

bacteriophage that incorporates itself into the host genome as a lysogenic prophage.

MC Enveloped viruses are usually released from the host cell by A. budding/exocytosis. B. lysis of the host cell. C. Endycytosis D. Phagocytosis

budding/exocytosis.

cytopathic effects (CPEs)

changes in a cells microscopic appearance due to virus-induced damage ex: syncytia, or inclusion bodies

inclusion bodies

compacted masses of viruses or damaged cell organelles, in the nucleus and cytoplasm

what are viral spikes typically composed of?

glycoproteins

MC What term is used to define the process of a prophage being activated and entering the lytic cycle

induction

viral envelope is composed of ___________

mainly lipids

In __________-sense RNA viral genomes, the RNA is not in a form ready for translation

negative

viral capsids are composed of mainly ______

protein

The enzyme ______ __________ is a preformed protein carried in by HIV responsible for converting its RNA genome into DNA.

reverse transcriptase

Lysogenic conversion

the bacterial acquisition of new genetic traits due to integration of prophage DNA

lysogeny

the indefinite persistence of bacteriophage DNA in a host without bringing about the production of virions

Transformation

the integration of an oncogenic virus that changes mammalian host DNA

transduction

when a phage transfers genes between bacteria gene recombination via bacteriophage transfer

MC Identify the viruses types that are released from host cells by lysis. A. complex B. enveloped C. naked

A & C complex and naked

prophage

A lysogenized bacteriophage; a phage that is latently incorporated into the host chromosome instead of undergoing viral replication and lysis

temperate phage

a bacteriophage that enters into a less virulent state by becoming incorporated into the host genome as a prophage instead of in the vegetative or lytic form that eventually destroys the cell

syncytia

a multi-nucleated protoplasmic mass formed by consolidated of individual cells result from some viruses ability to fuse membranes