Lecture Module 10: Virology

Viruses are obligate _____ that are only active inside a _____. They are _____ in size (< 0.2 um). They are not _____ nor are they _____ in nature. Their basic compact structure consists of a _____ shell (_____) surrounding a _____ core, which may be _____ or _____, but not both. They have a high _____ for attachment to host cells. They multiply by taking control of a host’s _____, producing new viruses. They lack the _____ and other machinery for most metabolic process.

Intracellular parasites; host; ultramicroscopic; alive; cellular; protein; capsid; nucleic acid DNA; RNA; specificity; genetic material; enzymes

A _____ is a fully formed virus that is able to establish an infection.

Virion

Viruses are classified by their type of _____, _____ strategy, and _____.

Nucleic acid; replication; morphology

The general structure of a virus consists of a covering and a central core. All viruses will have a _____ covering, while only some viruses will have an _____. All viruses will have a central core with either _____ or _____, while only some viruses will have _____.

Capsid; envelope; DNA; RNA; matrix proteins

A naked nucleocapsid has a _____ but no _____.

Capsid envelope

An enveloped virus has a _____ derived from a host’s _____ when the virus leaves the cell.

Phospholipid bilayer; cell membrane

Antimicrobial chemicals are more effective towards _____ (naked vs. enveloped) viruses because _____.

Enveloped; they can dissolve the phospholipid membrane found around the virus

The two parts of a nucleocapsid are the _____ and _____. Nucleocapsids are found in _____ viruses.

Nucleic acid; capsid; all

Nucleic acids found in viruses are either _____ or _____ but not both.

DNA; RNA

Viral DNA may be _____-stranded vs. _____-stranded, _____ vs. _____ in shape, and/or _____.

Single; double; linear; circular; segmented

Genes that are typically found in a viral genome are genes necessary to _____ and _____.

Invade host cells; redirect the cell’s activity to make new viruses

A capsid is a _____ coat that encloses and protects the _____ in a virus.

Protein; nucleic acids

_____ refer to the identical protein subunits that make up a capsid.

Capsomeres

The viral envelope is an extra covering _____ (inside vs. outside) the capsid that is derived from a _____ when the virus _____. Enveloped viruses are _____, meaning they have many shapes and a fluid structure. Viral envelopes allow viruses to _____ because they have the same _____ as the host and are therefore recognized as _____.

Outside; host cell membrane; leaves a host cell; pleomorphic; hide from the immune system; antigens self

Collectively, the capsid and envelope function to _____ the nucleic acids when the virion is outside a host cell, help _____ the virion to a cell surface, and assist in the penetration of viral _____/_____ into a suitable host cell.

Protect; bind; DNA/RNA

The spikes on a viral envelope refer to exposed carbohydrate-protein complexes on the outside of the envelope that function in the _____.

Attachment of a virus to a host cell

The 4 enzymes that viruses can produce are _____, _____, _____, and _____.

Polymerases; replicases; reverse transcriptase; lysozyme

Polymerases are viral enzymes that _____.

Synthesize new DNA or RNA

Replicases are viral enzymes that _____.

Make copies of RNA

Reverse transcriptase is a viral enzyme that _____. It is found in viruses that use _____.

Synthesizes DNA from RNA; RNA

Lysozymes are viral enzymes that _____. Lysozymes are found in _____.

Degrade cell walls; bacteriophages

A capsid that is _____ in shape consists of a hollow cylinder with nucleic acids inside.

Helical

A capsid that is _____ in shape has many sides. These capsids usually have _____ sides and are known as _____.

Polyhedral; 20; icosahedron

Other possible capsid shapes include _____ shapes, which have multiple different types of morphology, and _____ shapes, which are roughly spherical, but polymorphic.

Complex; enveloped

The 6 steps in animal virus replication are _____/_____, _____, _____, _____, _____, and _____.

Adsorption/attachment; penetration; uncoating; synthesis; assembly; release

During adsorption/attachment in animal virus replication, a virus _____ collides with a susceptible host cell and adsorbs to a _____ receptor site on the cell membrane.

Randomly; specific

During penetration in animal virus replication, the _____.

Genome enters the host cell

During uncoating in animal virus replication, the _____.

Viral nucleic acid is released from the capsid

During synthesis in animal virus replication, _____.

Viral components are produced

During assembly of animal virus replication, _____.

New viral particles are constructedDUrin

During release of animal virus replication, _____.

Assembled viruses are released by budding (exocytosis) or cell lysis

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

False; individual viruses bind to specific molecules on a given host cell

Host range refers to the _____. Host range depends on the _____.

Spectrum of cells a virus can infect; availability of appropriate attachment sites on the surface of a host cell

Hepatitis B has a _____ host range because it infects _____.

Narrow; human liver cells only

Rabies has a _____ host range because it infects _____.

Broad; multiple types of mammalian cells

Virus adsorption always occurs via _____ for animal viruses. With enveloped viruses, the virus uses _____ located on the cell envelope to bind to the host cell. With naked viruses, the virus uses _____ located on the corners of the _____ to bind to the host cell.

Receptors; spikes; small fibers; icosahedron

The two ways in which animal viruses penetrate host cells are _____ and _____.

Receptor-mediated endocytosis; fusion

During receptor-mediated endocytosis when an animal virus penetrates a host cell, _____ attachment leads to _____, the packaging of the virus in a _____, and then _____.

Specific; engulf; vesicle; uncoating

During fusion when an animal virus penetrates a host cell, _____ and the host cell receptors fuse, producing a _____ that allows only the _____ to enter, not the _____, before _____.

Spikes; receptor-spike complex; nucleocapsid; envelope; uncoating

_____/_____ refers to process in which viruses are gradually released by an infected cell, and the cell does not lyse immediately.

Budding/exocytosis

During budding/exocytosis, the _____ binds to the host cell membrane, which _____, creating an _____.

Nucleocapsid; pinches; envelope

_____ refers to the process in which non-enveloped and complex viruses are released when the cell dies and ruptures.

Lysis

During lysis, _____ and _____ viruses are released when the cell dies and _____.

Non-enveloped; complex; ruptures

3 ways that animal viruses are grown in the lab are inside _____, _____, or _____.

Living animals; embryonated eggs; cell cultures

When animal viruses are grown inside embryonated eggs, viruses are _____ into the eggs, and viral growth is signaled by _____ or _____ in the embryo.

Injected; changes; death

When animal viruses are grown inside cell cultures, tissues are treated with enzymes to separate cells, and virally infected cells are detected via _____/_____.

Deterioration/cytopathic effects

Cytopathic effects refer to _____. Examples include changes in _____ or _____, _____ or _____ inclusion bodies, cells that fuse to form _____ cells, cell _____, altered _____, or cells that have become _____.

Virus-induced damage to a cell; size or shape; cytoplasmic or nuclear; multinucleated cells; lysis; DNA; cancerous

Viruses are identified through _____, _____, or _____, with the second being the most common.

Cytopathic effects; serological tests; nucleic acids

During serological tests to identify a virus, _____ is used to determine the reaction of the virus with various antibodies.

Western blotting

When using nucleic acids to identify a virus, _____ is used to amplify and detect viral DNA.

PCR

The 3 main categories of antiviral drugs are _____, _____, and _____ inhibitors.

Entry; nucleic acid synthesis; assembly and release

Entry inhibitor antiviral drugs work by inhibiting _____, _____, and _____.

Attachment; fusion; uncoating

Nucleic acid synthesis inhibitor antiviral drugs work by inhibiting _____, _____, and _____.

Viral polymerase; reverse transcriptase; integrase

Assembly and release inhibitor antiviral drugs work by inhibiting _____, an enzyme needed to clip viral proteins into function pieces.

Protease

Interferons are used to _____. Interferons are produced naturally by virally-infected cells to _____ and _____.

Prevent the spread of viruses to new cells; magnify the immune response; inhibit viral replication

In order for a virus to multiply in a host cell, the virus must _____ and _____.

Invade a host cell; take over the host cell’s metabolic machinery

Acute infections refer to infections with a _____ onset, relatively _____ period of infection, and resolution within _____. An example of an acute infection is the _____.

Rapid; short; days; common cold

Latent infections refer to infections in which the virus remains in an _____ host cell for _____ periods of time, usually without being _____. They may reactivate due to changes in _____. An example of a latent infection is _____, which causes _____.

Asymptomatic; long; released; immunity; varicella; shingles

Persistent infections refer to infections in which infection occurs _____ over a _____ period of time. These infections are generally _____. An example of a persistent infection is _____, which causes _____.

Gradually; long; fatal; HPV; cervical cancer

_____ refer to mammalian viruses capable of initiating tumors.

Oncoviruses

Some animal viruses enter host cells and permanently alter genetic material, resulting in _____. Transformed cells have an increased rate of _____, alterations in their _____, and the capacity to _____ for indefinite periods of time, resulting in _____.

Cancer; growth; chromosomes; divide; tumors

_____ refer to viruses that infect bacteria.

Bacteriophages

The multiplication of bacteriophages is similar to animal viruses, but only the _____ enters the cytoplasm (the _____ does not), and release occurs via _____ only.

Nucleic acid; capsid; cell lysis

_____ happens in animal virus multiplication, but not bacteriophage multiplication.

Uncoating

Bacteriophages are grown in the laboratory using _____.

Bacteria

A plaque refers to _____. Each plaque corresponds to a _____, which is known as a _____.

Clearings on a lawn of bacteria; single virus; plaque-forming unit

The 5 stages of the lytic cycle of bacteriophage multiplication are _____, _____, _____, _____, and _____.

Attachment; penetration; biosynthesis; maturation; release

During attachment in the lytic cycle of bacteriophage multiplication, the phage uses _____ to _____.

Tail fibers; attach to the host cell

During penetration in the lytic cycle of bacteriophage multiplcation, the phage _____ opens the _____, and the _____ contracts to force the _____ and _____ into the cell.

Lysozyme; cell wall; tail sheath; tail core; DNA

During biosynthesis in the lytic cycle of bacteriophage multiplication, _____.

Phage DNA and proteins are produced

During maturation in the lytic cycle of bacteriophage multiplication, phage particles are assembled into _____, complete infectious viruses.

Virions

During release in the lytic cycle of bacteriophage multiplication, the phage _____ breaks the _____.

Lysozyme; cell wall

_____/_____ allow a bacteriophage to attach to host cell walls/cell receptors.

Fibers at the end of the tail; tail sheath

Phages produce _____ to break down bacterial cell walls so that they may inject their DNA into a host cell.

Lysozyme

Phages are released from bacterial cells via _____ only.

Lysis

Bacteria may acquire the ability to produce toxins when they are infected with _____ phages.

Lysogenic

In the lysogeny/lysogenic cycle of a bacteriophage, the phage remains _____, meaning it is not _____, resulting in _____ phages.

Latent; actively making new phage particles; temperate

During the lysogenic cycle in bacteriophages, the phage DNA _____, where it becomes known as a _____. When the host cell replicates its chromosome, _____ results in the host cell _____.

Incorporates into host cell DNA; prophage; phage conversion; exhibiting new properties

Prions refer to _____ infectious particles that result in transmissible _____, resulting in fatal _____ diseases. Prions are _____ and extremely _____ to usual sterilization techniques.

Proteinaceous; spongiform encephalopathies; neurodegenerative; misfolded; resistant

Satellite viruses refer to viruses that are _____.

Dependent on other viruses for replication

Viroids refer to _____.

Short pieces of RNA with no protein coat