Microbiology Chapter 13

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virus

tiny infectious agent with nucleic acid surrounded by capsomeres

capsomeres

protein subunits of capsids that surround viruses

common characteristics of viruses, viroids, and prions

lack cell structure
cannot metabolize, grow or self-produce
cannot respond to the environment

capsid

the coating of protein surrounding the nucleic acid of a virus

virion

a complete viral article, including a nucleic acid and a capsid, outside of a cell

bacteriophage

a virus that infects a bacterial cell

How are viruses classified?

type of nucleic acid,
presense of an envelope,
shape,
size

5 stages of the replication cycle of a virus

attachment, entry, synthesis, assembly, release

Viruses depend on _________________.

random contact with a specific host cell type for replication

uncoating

process by which the capsid is removed after the virion enters the cell

latency

animal virus remains inactive in a cell as part of a chromosome or in the cytosol

provirus

the viral DNA which inserts into a host cell's chromosome

dsDNA virus

in a virus, acts like cellular DNA in transcription and replication

ssRNA virus

has positive-strand RNA which can be directly translated by ribosomes to synthesize protein

positive-strand RNA

same polarity as MRNA so genome RNA can be translated in cytoplasm by host cell ribosomes

negative-strand RNA

complementary to mRNA, genome must be transcribed by viral RNA polymerase to produce viral RNA

neoplasia

uncontrolled cell reproduction in a multicellular animal

tumor

mass of neoplastic cells

neoplastic cells

Tumor (abnormal function, unregulated growth
"steals nutrients from other tissues")

oncogenic virus

viruses that lead to cancer by permanently altering its genetic material

How are viruses cultured in a lab? Why?

inside mature organisms or embryonated chicken eggs, because viruses cannot metabolize or replicate alone

plaques on the bacterial lawn

clear areas on a agar plate where bacteria has been infected with phages lyse

phages

viruses that infect bacteria

lyse

to burst

plaque assay

Determines the number of viruses in solution. A known volume of solution is added to metabolizing cells, and the infection lyses cells and leads to a clear zone or plaque surrounded by uninfected cells. Each plaque represents one virion.

2 types of cell cultures on which viruses can be grown

diploid cell cultures and
continuous cell cultures

diploid cell cuture

last 100 generations

continuous cell cultures

derived from cancer cells, last longer than diploid cell cutures

viroids

small circular pieces of RNA with no capsid that infect and cause disease in plants

prions

infectious protein particles that lack nucleic acids and replicate by coverting similar, normal proteins into new prions, cause diseases such as spongiform encephalopathies

spongiform encephalopathies

disease caused by prion aggregates that cause nervous degradation. known as Creutzfeld-Jacobs Disease, Mad Cow, Scrapie

Which of the following is not an ancellular agent?
a. viroid
b. virus
c. rickettsia
d. prioin

c. rickettsia

Which of the following statements is true?
a. viruses move toward their cell hosts
b. viruses are capable of metabolism
c. viruses lack a cell membrane
d. viruses grow in response to their environmental conditions

c. viruses lack a cell membrane

A virus that is specific for a bacterial host is called a
a. phage
b. prion
c. virion
d. viroid

a. phage

A naked virus
a. has no membranous envelope
has injected its DNA or RNA into a host cell
is devoid of capsomeres
is one that is unattached to a host cell

a. has no membranous envelope

Which of the following statements is false?
a. viruses may have circular DNA
b. dsRNA is found in bacteria more often than in viruses
c. viral DNA may be linear
d. typically, viruses have DNA or RNA, but not both

b. dsRNA is found in bacteria more often than in viruses

When a eukaryotic cell is infected with an enveloped virus and sheds viruses slowly over time, this infection is
a. called a lytic infection
b. a prophage cycle
c. called a persistent infection
d. caused by a quiescent virus

c. called a persistent infection

Another name for a complete virus is
a. virion
b. viroid
c. prion
d. capsid

a. virion

Which of the following viruses can be latent?
a. HIV
b. chickenpox virus
c. herpesviruses
d. all of the above

d. all of the above

Which of the following is not a criterion for specific family classification of viruses?
a. the type of nucleic acid present
b. envelope structure
c. capside type
d. lipid composition

d. lipid composition

A clear zone of phage infection in a bacterial lawn is
a. a prophage
b. a plaque
c. naked
d. a capsomere

b. a plaque

uncoating

the removal of a viral capsid within a host cell

prophage

an inactive bacteriophage, which is inserted into the host's chromosome

retrovirus

any +ssRNA virus that uses the enzyme reserve transcriptase carried within its capsid to transcribe DNA from its RNA (ex-HIV)

bacteriophage

virus that infects and usually destroys bacterial cells

capsid

a protein coat surrounding the nucleic acid core of a virion

envelope

membrane surrounding the viral capsid

virion

a virus outside of a cell, consisting of a proteinaceous capsid surrounding a nucleic acid core

provirus

inactive virus in an animal cell

benign tumor

mass of tumor cells that remains in one place and is not generally harmful

bacteriophage cycle

1. attachment
2. entry
3. synthesis
4. assembly
5. release

5 phases of a generalized lytic replication cycle

1. Attachment of the virion to the host cell.
2. Entry of the virion into the host cell
3. Synthesis of new nucleic acids and viral proteins by the host cell's enzymes and ribosomes.
4. Assembly of new virions within the host cell.
5. Release of the new virons from the host cell.

Why is it difficult to treat viral infections?

Viruses live inside the body's cells and take control of the cell's metabolsim. They are "protected" from medicines, which usually move through the bloodstream. Antibiotics do not work for viral infections. There are a few antiviral medicines available.

Describe 3 different ways that viral nucleic acid can enter a host cell.

Direct penetration, membrane fusion, endocytosis

Contrast lysis and budding as a means of release of virions from a host cell.

Viruses can be released from the host cell by lysis, a process that kills the cell by bursting its membrane and cell wall if present. Enveloped viruses (e.g., HIV) typically are released from the host cell by budding. During this process the virus acquires its envelope, which is a modified piece of the host's plasma or other, internal membrane.

What is the difference between a virion and a virus particle?

A virion is a virus outside of a cell, Virus particles resemble viruses, but are non-infectious because they do not contain any viral genetic material

How is a provirus like a prophage? How is it different?

A provirus is an inactive virus in an animal cell. A prophage is an inactive bacteriophage which is inserted into a host's chromosome. They are both latent but some proviruses do not become incorporated into the chromosomes of their hosts cells and phages always do. Also some animal viruses like HIV do become part of the host chromosome as a provirus and they are a permanent, physical part of the te host's chromosome, and all descendants of the infected cell will carry the provirus.

Describe lysogeny.

a dormant viral infection of bacteria in which the genetic material of a virus combines with that of a host bacterium

How are viruses specific for their host's cells?

Viruses have proteins on their capsule that bind preferentially to certain receptors on cells. This is why viruses can selective bind certain types of cells. For example, HIV has a protein on its surface that is specific for receptor proteins on immune cells. This is why HIV selectively infects and attacks the immune system.

Compare and contrast diploid cell culture and continuous call culture.

Diploid cell cultures are created from embryonic animal, plant or human cells and last no more than 100 generations. Continuous cell cultures last longer because they are derived from tumor cells and can last indefinitely.

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