BIO 112 - Chapter 27: Viruses

What are the steps in infection for most phage?

attachment, injection of DNA (penetration), macromolecular synthesis, assembly of new phage, and release of progeny phage

Give an example of a disease caused by a virus with a double-stranded DNA genome.

chicken pox, hepatitis B, herpes, mononucleosis, smallpox

How is the infectivity of viruses reduced?

each virus has a limited host range and many also exhibit tissue tropism

Give an example of a disease cause by a virus with a (-) single-stranded RNA genome.

ebola, influenza, measles, SARS, rabies

What is a prophage? (lysogen)

integrated phase of the genome

What occurs during assembly?

involves spontaneous assembly of capsid and enzyme to insert DNA

What is a isoahedron?

is a structure with 20 equilateral triangular facets

What is a host range?

is what the suitable cells for a particular virus are referred to

Describe phage conversion.

is when characteristic of the the lysogenic bacterium is altered by the prophage

What is special about Mimivirus?

it is the size of a small bacterium, wit a megabase-sized genome; the genome encodes parts of the translation apparatus

What is a cell containing a prophage called?

lysogen

Describe CD4+ cells.

relevant cells the produce the CD4 antigen that are targeted by HIV

Describe viruses.

strands of nucleic acids encased in a protein coat; consist of either DNA or RNA; most have a protein sheath or capsid around their nucleic acid core; some also have enzymes in their capsid

Describe viral genomes.

viral genomes exhibit great variation; DNA or RNA viral genome may be linear or circular, single- or double-stranded; RNA viruses may have multiple RNA molecules (segmented) or only one RNA molecule (non segmented); retroviruses contain RNA that is transcribed as DNA by reverse transcriptase

What occurs during attachment?

virus contacts and becomes specifically bound to the cell

When does phage conversion occur?

when foreign DNA is contributed to the host by a bacterial virus

Give an example of a disease caused by a virus with a (+) single-stranded RNA genome.

AIDS, polio, west nile fever

Define viroids.

Any group of small, naked RNA molecules that are capable of causing plant diseases , presumably by disrupting chromosome integrity.

Why was prion replication a heretical suggestion?

Because they are proteinaceous infections particles consisting of a misfolded form or protein. The misfolding catalyzes a chain reaction of misfolding in normal proteins, causing disease. (Mad Cow disease)

What are viroids?

Circular naked molecules of RNA that infect plants and use post protein to replicate

The reverse transcriptase enzyme is active in which class of viruses?

Double Stranded DNA virus

What phases of HIV life does an AIDS treatment target?

Drugs target replication, protein maturation, viral entry, and genome integration.

Which of the following is common in animal viruses but NOT in bacteriophage? (DNA, capsid, Envelope, Icosahedral shape)

Envelope

Discuss the Type A flu virus.

It causes the most serious flu epidemics in humans and also occurs in mammals and birds.

What occurs during release?

Mature virus particles are produced.

What does temperate mean? (lysogenic)

A virus that is capable of incorporating its DNA into the host cells DNA; where it remains for a length f time and is replicated as the cell replicates.

Why does HIV have a high mutation rate?

Reverse transcriptase enzyme is much less accurate than DNA polymerases.

Which of the following terms is not a part of a virus? (Capsid, Ribosomes, Genetic material, or are they all found in viruses?)

Ribosomes

What are the three classifications for viruses?

1) DNA virus 2) RNA virus 3) retrovirus

What does AIDS stand for? What causes AIDS (give the full name and abbreviation)?

1) acquired immunodeficiency syndrome 2) human immunodeficiency virus (HIV)

What are the two most common shapes of viruses?

1) helical (rodlike) 2) icosahedral (spherical)

What are the two reproductive cycles of viruses?

1) lytic cycle 2) lysogenic cycle

What does HIV target? Why does this lead to death?

1) targets macrophages and CD4+ cells, a type of helper T-lymphocyte cell 2) the loss of these cells prevents the body from fighting off opportunistic infections, which ultimately lead to death

Describe the process of how HIV infects cells.

1) the viral glycoprotein gp120 precisely fits on the cell surface marker protein CD4+ on macrophages and T-cells. When the HIV attaches to two receptors, CD4+ and CCR5, receptor-mediated endocytosis is activated bringing the HIV particle into the cell 2) Once inside the cell, the protective coat is shed, releasing viral RNA and reverse transcriptase into the cytoplasm. Reverse transcriptase makes double-stranded DNA complementary to the viral RNA. This DNA may be incorporated into the host DNA as a provirus. 3)Replicated viruses are budded off the host cell by exocytosis.

Describe severe acute respiratory syndrome (SARS).

A emerged species coronavirus was responsible for the 2003 world wide outbreak; respiratory infections with pneumonia like symptoms. Fatal in 8% of cases.

A process by which a virus may change a benign bacteria into a virulent strain is called:

Induction

Define prion.

Infectious proteinaceous particles

Which of the following would NOT be part of the life cycle of a lytic virus? (macromolecular synthesis, attachment to host cell, assembly of progeny virus, integration into the host genome)

Integration into the host genome

What is the hantavirus?

Is a single stranded RNA associated rodents. Sudden outbreak caused deadly pneumonia in SW US in 1993. Ex. of an emerging virus.

Describe a capsid.

Protein sheath around the nucleic acid core

What is tissue tropism?

The affinity of a virus to target certain cells when inside a multicellular host (ex. hepatitis and liver cells )

What was the most lethal virus in human history? What does it infect?

Type A influenza viruses infect mammals and bird?

Why must flu vaccines be updated?

Viruses recombine genes frequently, and the immune system (antibodies) cannot recognize viruses.

Explain what an emerging virus is.

Viruses that originate in one organism and then pass to another and cause disease.

Can viruses cause cancer?

Yes, they have been linked to formation of cancers. HPV and cervical cancer are good examples.

What is the difference between the lytic cycle and the lysogenic cycle?

the lytic cycle kills the host cell, whereas the lysogenic cycle incorporates the virus into the host genome as a prophage

What are T-helper cells?

the specific cell type infected by HIV; regulates immune response

What occurs during synthesis?

the virus takes over the cell's replication and protein synthesis machinery in order to synthesize viral components

How do viruses replicate?

they lack the ribosomes and proteins needed for replication so they take over host machinery and direct their own nucleic acid and protein synthesis

What is latent? (in terms of viruses)

this means dormant, the virus can hangout for seconds, days, weeks, months, or years then boom you're sick again.

What occurs during penetration?

viral DNA injected into cell