Chapter 13

Question 1

1. Q: What are the structural components of a virus?

Answer 1

A: Nucleic acid, capsid, envelope, and spikes.

Question 2

Q: What is “host range”? What determines it?

Answer 2

A: Host range is the spectrum of hosts a virus can infect. It’s determined by the virus’s ability to attach to the host cells via specific receptor sites.

Question 3

Q: What is the viral one-step growth curve?

Answer 3

A: 1) Inoculation: Virons attach to host cell
2) Eclipse: Entry of Viral Genome
3) Burst: Sufficent # of virons are produced and emerge from host cell

Question 4

Q: What is the difference between the lytic and lysogenic cycle of bacteriophages?

Answer 4

A: The lytic cycle destroys the host cell through reproducing, while the lysogenic cycle integrates the viral DNA into the host’s genome replicating itself with the hosts machinery.

Question 5

Q: What are the five steps of bacteriophage infection?

Answer 5

A: Attachment: Phage attaches by tail fibers
Penetration: Phage lysozyme enzyme opens
Biosynthesis: Production of cell DNA and Protein
Maturation: Assembly of Phage Particles
Release: Phage Lysozyme breaks cell wall

Question 6

Q: Name six steps of animal virus infection.

Answer 6

A: Attachment: Phage attaches by tail fibers
Entry: Entry through receptors mediated endocytosis or fusion.
Uncoating: Through viral or host enzymes
Biosynthesis: Production of cell DNA and Protein
Maturation: Assembly of Phage Particles
Release: Through budding(enveloped viruses) or rupture(like a white head)

Question 7

Q: Name some DNA and RNA viruses and associated diseases.

Answer 7

A: Smallpox (Variola), Chickenpox/Shingles (Varicella-Zoster), Herpes Simplex, Poliovirus, Lyssavirus (Rabies), Influenza virus, Lentivirus (HIV), Coronavirus.

Question 8

Q: What are oncogenes?

Answer 8

A: Genes that can cause cancer when mutated or overexpressed, leading to transformed cells with uncontrolled growth.

Question 9

Q: Define persistent, latent, and acute infections with examples.

Answer 9

A: Persistent: Long-term (e.g., HIV); Latent: Dormant and reactivates (e.g., HSV, Chickenpox); Acute: Short-term (e.g., influenza).

Question 10

Q: What are prions, and what diseases do they cause?

Answer 10

A: Infectious proteins that cause neurodegenerative diseases like Creutzfeldt-Jakob disease.

Question 11

Q: What type of virus is SARS-CoV-2?

Answer 11

A: An RNA (+) virus that targets cells in the respiratory system; COVID vaccines aid in immune response.

Question 13

Virus General characteristics(not its features)

Answer 13

Obligate intracellular parasite

Either DNA or RNA but never both

Protein coat

Contain few to no enzymes ~ metabolism

Uses hosts machinery to reproduce

Question 14

Nucleic Acid

Answer 14

DNA or RNA

Question 15

Capsid

Answer 15

Composed of protein subunits called capsomeres

Question 16

Envelope

Answer 16

A protective layer that envelopes usually consists of lipids, carbs, and proteins

Question 17

Spikes

Answer 17

Protrusions, sometimes for attachment

Question 18

Lysogenic cycle

Answer 18

Virus DNA enters host, incorporates into host DNA to “hide
out”. It replicates along with the host DNA but eventually
can excise itself (viral DNA is cut out) and the virus enters
the Lytic cycle

Question 19

Smallpox(Variola)

Answer 19

Orthopox Virus - Double stranded virus

Transmitted via respiratory system

Some strains can become latent and reactivated through stress

Prevented through vaccine(zoster)

Affects nerve fibers and skin

Question 20

Poliovirus

Answer 20

Transmitted through ingestion of feces contaminated water

Initial symptoms are sore throat and nausea

Viremia: Virus appears in blood

One percent of cases become paralytic

Destruction of motor cells

*persistent strains still exist

Question 21

Lyssavirus(Rabies)

Answer 21

Bullet Shaped

Single stranded RNA; easily develops mutants

Usually transmitted by animals saliva - also through mucus membranes

Silver haired bats

Muscle spasms of the mouth and pharynx

Virus multiples in skeletal system

30-50 day incubation

Forms negri bodies in brain stem

Question 22

Herpes simplex

Answer 22

Human herpes:

HSV 1: Oral
HSV 2: Sexual

Rarely spreads to brain but not impossible

Latent and can be trigger by a multitude of factors such as stress

Question 23

Lentivirus(HIV)

Answer 23

Two identical + stranded RNA genome molecules,
reverse transcriptase enzyme, integrase enzyme and
a phospholipid envelope

Single Standed

Uses Reverse Transcriptase

Oncogenic(includes all rna tumor viruses)

Question 24

HIV Treatment

Answer 24

Drugs target multiple enzymes at once
1. Blocks reverse transcriptase (Reverse Transcriptase inhibitors)
2. Blocks entry of virus into cells (Fusion inhibitors, CCR5 antagonist)
3. Blocks virus DNA into host DNA (Integrase inhibitors)
4. Fusion inhibitors
5. Disrupts building blocks needed for viral replication (Protease inhibitors)

Question 25

Oncogenes

Answer 25

Genes that when are over active, and can transform normal cells into cancerous cells

Question 26

Oncogenic viruses

Answer 26

When a virus carries an oncogene in its viral genome which can then become integrated into the host cells DNA and induce tumors in those cells

Question 27

DNA Oncogenic viruses(names)

Answer 27

1. Adenoviridae
2. Herpesviridae
   – Epstein-Barr virus
3. Poxviridae
4. Papovaviridae
   – Human papillomavirus (cervical and anal cancers)
5. Hepadnaviridae
   – Hepatitis B virus(liver cancer)

Question 28

Persistent Infection

Answer 28

A persistent viral infection occurs gradually over a
long period; is generally fatal
– Subacute sclerosing panencephalitis (measles
virus)

Question 29

Latent Viral Infection

Answer 29

Latent virus remains in asymptomatic host cell for
long periods
– May reactivate due to changes in immunity
§ Cold sores, shingles

Question 30

Prions

Answer 30

• Proteinaceous Infectious particle
• Inherited and transmissible by
ingestion, transplant, and surgical
instruments

Question 31

Prions chemical identity

Answer 31

• PrPC: normal cellular prion protein, on the cell surface
• PrPSc: scrapie protein; accumulates in brain cells,
forming plaques