Chapter 13

A single virus particle could contain a genome of...

either RNA or DNA

In which ways do newly assembled viruses leave their host cells?

Apoptosis or budding

HIV is a RNA retrovirus. What happens once it enters a cell?

Reverse transcriptase from the cirus converts HIV RNA to DNA & the genes from HIV are incorporated into the host cell genome.

Acute infections of animals...

are a result of product infection & generally lead to long-lasting immunity

A (n) ______ viral infection is characterized by the continuous, low-level production of new virus particles by animal host cells

chronic

Non-enveloped viruses generally are more resistant to disinfectants than are enveloped viruses because...

disinfectants damage the lipid bilayer of the envelope

All phages must be able to... (2 things)

inject their nucleic acid into a host cell & have their nucleic acid replicate in the host cell

Infection of bacteria by ______ phages always ends w/lysis of the host cell

lytic

What best describes viruses?

obligate intracellular infectious agents

Viral infections that result in the formation of new virus particles are described as which of the following types of infection?

productive

Capsids are composed of...

proteins

Out of human cells, bacteria, viruses, and protozoa - which is the smallest?

viruses

Classification of viruses are not based on...

SIZE of virus

Phages infect which of the following cells?

ONLY bacteria cells

Prions are composed of what? And what do they cause?

Solely of protein and cause a number of transmissible spongiform encephalopathies

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

Through feces, coughing & sneezing, and from animals to humans

Lytic phage infections

-exit host @ end of cycle by lysing the cell 1. Attachment- phage attaches to specific receptors on host cell wall 2. Genome Entry- the tail contracts and phage DNA is injected into the bacterial cell, leaving the phage coat outside 3. Synthesis- phage genome is transcribed and phage proteins synthesized. Phage DNA is replicated, other virion components are made and host DNA is degraded 4. Assembly- Phage components are assembled into mature virions 5. Release- The bacterial cell lyses and many new infectious virions are released

Two methods used to quantitate animal viruses

1: "Plage assays," which reoly on lysis of host cells 2: counting of virions using an "electron microscope." The concentration of virions must be high enough to be seen. 3: "Hemagglutiation assays"

How does a vaccine prevent cervical cancer?

A vaccine against HPV precents the infection of cells and the synthesis of virus proteins which appear to be responsible for the cancer.

Acute infections and what bacteriophage infection can they be compared to?

Acute infections are characterized by sudden onset of symptoms of relatively short duration. On a cellular level, they can be compared to productive lytic infections by bacteriophages.

Distinguish between acute and persistent viral infections at the cellular level

Acute infections: the cirions kill the host cells Persistent infections: virus does not kill the host cells

How do enveloped viruses exit a cell?

By budding

How are latent viral infections different from chronic infections?

Chronic infections: viral particles are produced continously from infected cells, often w/o causing symptoms Latent infections: viral genome is silent but can be activated to once again cause disease

Two types of persistent infections and what bacteriophage infection can they be compared to?

HIV & Hep B latent infections are analougous to lysogeny in bacteriophages

What is the role of a prophage in persistent infections?

In the latent form of the temperate phage, the phage DNA has been inserted into the host's DNA (now called prophage). It is a repressor that maintains the prophage in an integrated state, but the prophage can be excised to initiate a lytic infection

Why is it virtually impossible to eradicate a disease caused by zoonotic virus?

It would be impossible to eradicate all of the animal hosts

Steps of an animal virus infection cycle in correct order... -Attachment -Release -Synthesis of viral proteins and replication of the genome -Assembly -Penetration and uncoating

(1) attachment (5) release (3) synthesis of viral proteins and replication of the genome (4) assembly (2) penetration and uncoating

Where does an enveloped virus get its envelope?

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

What do virus particles NOT have: -protein capsid -mitochondrion -nucleic acid -metabolic pathways

Mitochondrion & metabolic pathways

Temperature phage infections

Temperate phages have the option to either direct a productive infection (lytic) or initiate a lsogenic infection. The infected cell called a lysogen. A repressor maintains a prophage in an integrated state, but the prophage can be excised to initiate a lytic infection

The enteric viruses are a group of taxonomically unrelated viruses that are grouped together because:

They are transmitted by the fecal-oral route

In tissue culture, why is it advantageous to use tumor cells rather normal cells?

Tumor cells multiply indefinitely in contrast to normal cells which stop multiplying after a certain number of gens

An enveloped virus gets its envelope from...

a host cell membrane

A viral infection in which the viral genome is integrated into a host cell chromosome is categorized as a _______ infection in bacteria and a _______ infection in animals.

lysogenic, latent