Microbiology Ch.13

How are plant viruses transmitted?

- Soil - Humans- - Insects - Contaminated seeds, tubers, pollen - Grafting

Distinguish between a viroid and a prion in terms of structure and hosts

Viroids consist of short segments of RNA and infect only plants. Prions consist only of protein and infect only animals, including humans.

Could the same type of virus cause both an acute and a persistent infection? Explain.

Yes, the initial infection might be acute but the virus can later become latent by becoming integrated into the host cell genome.

What are plaque-forming units?

a quantitative measure of the number of phage particles as measured by a plaque assay

A virus that infects bacteria; often shortened to phage

bacteriophage

viral infection in which the viral genome is present but not active, so new viral particles are not being produced.

latent infection

viral infection of a host cell with a subsequent production of more viral particle and lysis of the cell

lytic infection

viral infection in which more viral particles are produced

productive infection

Which is more likely to be a specialized transducing phage- a lytic or temperate phage?

temperate phase

What is the role of a prophage in persistent infections?

the prophage can be activated and once again cause disease

a complete virus in its inert non-replicating formal also referred to as a viral particle.

virion

an infectious agent of plants that consists only of RNA

viroid

What is lysogenic conversion?

The modification of certain properties of a bacterial cell as a result of carrying a temperate phage in its genome. The new properties are encoded in the phage DNA.

List 3 ways in which viruses can be transmitted from one organism to another

1). Through feces (enteric viruses) 2). Through coughing and sneezing (respiratory viruses) 3). From animals to humans (zoonotic viruses)

How is the replication cycle of lambda phage different from that of T4?

The genome of lambda phage can integrate in the bacterial genome and replicate in concert with the bacterial DNA. T4 cannot do this but undergoes a replication cycle that results in cell lysis.

Acute infections of animals

1. are a result of productive infection & 2. Generally lead to long-lasting immunity

All phages must be able to

1. inject their nucleic acid into a host cell & 5. Have their nucleic acid replicate in the host cell

The tail fibers on phages are associated with

A. attachment

Determining viral titers of both phage and animal viruses frequently involves

A. plaque formation

What is the difference between acute and persistent infections?

Acute- rapid, onset, short duration, kills host cells Persistent- continue for years or lifetime, may or may not have symptoms, does not kill cells

Where does an enveloped virus gets its envelope?

An enveloped virus acquires its envelope from the host cell as it exists that cell, by picking up some of the host cell cytoplasmic membrane.

Filamentous phages

C. are extruded from the host cell

Capsids are composed of

C. protein

Classification of viruses is based on all of the following except

C. size of virus

Temperate phages can do all of the following except

D. bud from their host cells

Prions

D. cause disease of humans

Influenza vaccines must be changed yearly because the amino acid sequence of the viral proteins changes gradually over time. Based on this information, which is the most logical conclusion? The influenza virus

D. has an RNA genome

Why are non-enveloped viruses generally more resistant to disinfectants than are enveloped viruses?

Disinfectants damage the lipid bilayer of the envelope

Distinguish between acute and persistent viral infections at the cellular level.

In acute infections, the visions kill the host cells whereas in persistent infections, the virus does not kill the host cells.

How are latent viral infections different from chronic ones?

In chronic infections, viral particles are produced continuously from infected cells, often without causing symptoms. In latent infections, the viral genome is silent but can be activated to once again cause disease.

How is specialized transduction different from generalized transduction?

In specialized transduction, only genes near the site on the bacterial chromosome where the phage has integrated can be transduced. In generalized transduction, any gene of the bacterial genome can be transduced.

Why would it be advantageous to a virus to interfere with the function of proto-oncogenes or tumor suppressor genes?

Interfering with the function of these genes would result in uncontrolled cell growth and thus more cells that could be invaded by the viruses, leading to increased virus production.

a bacterium that carries phage DNA (a prophage) integrated into its genome

Lysogen

a change in the properties of a bacterium, conferred by a prophage

Lysogenic conversion

Most enteric viruses are non-enveloped. Why would this be so?

Naked viruses are more resistant to various chemicals which the enteric viruses are likely to encounter as they are transmitted by the fecal-oral route

an infectious protein that causes a neurodegenerative disease

Prion

Discuss how prion proteins accumulate in nervous tissue

Prion proteins accumulate because they are resistant to proteases which break down proteins and they also convert a normal cellular protein which is continually synthesized to the prion protein, thereby increasing the concentration of prion protein.

How do oncogenes differ from proto-oncogenes?

Proto-oncogenes stimulate routine cell growth and division. Oncogenes are modified pro to-oncogenes that promote uncontrolled cell growth.

Give an example of a virulent phage and of a temperate phage?

T4 is a virulent phage and lambda is a temperate phage.

Describe how the replication cycle of T4 phage is different from that of lambda.

T4 phages are lytic phages- they integrate their genome into that of the host cell and may remain there as prophages. They do not cause the death of the host cell unless environmental conditions cause the phage to enter a lytic life cycle.

Describe how prions propagate

The abnormal prion protein binds to the normal cellular normal prion protein and changes its conformation, converting it to the abnormal form.