Chapter 13 Flashcards
- Q: What are the structural components of a virus?
A: Nucleic acid, capsid, envelope, and spikes.
Q: What is “host range”? What determines it?
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.
Q: What is the viral one-step growth curve?
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
Q: What is the difference between the lytic and lysogenic cycle of bacteriophages?
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.
Q: What are the five steps of bacteriophage infection?
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
Q: Name six steps of animal virus infection.
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)
Q: Name some DNA and RNA viruses and associated diseases.
A: Smallpox (Variola), Chickenpox/Shingles (Varicella-Zoster), Herpes Simplex, Poliovirus, Lyssavirus (Rabies), Influenza virus, Lentivirus (HIV), Coronavirus.
Q: What are oncogenes?
A: Genes that can cause cancer when mutated or overexpressed, leading to transformed cells with uncontrolled growth.
Q: Define persistent, latent, and acute infections with examples.
A: Persistent: Long-term (e.g., HIV); Latent: Dormant and reactivates (e.g., HSV, Chickenpox); Acute: Short-term (e.g., influenza).
Q: What are prions, and what diseases do they cause?
A: Infectious proteins that cause neurodegenerative diseases like Creutzfeldt-Jakob disease.
Q: What type of virus is SARS-CoV-2?
A: An RNA (+) virus that targets cells in the respiratory system; COVID vaccines aid in immune response.
Virus General characteristics(not its features)
Obligate intracellular parasite
Either DNA or RNA but never both
Protein coat
Contain few to no enzymes ~ metabolism
Uses hosts machinery to reproduce
Nucleic Acid
DNA or RNA
Capsid
Composed of protein subunits called capsomeres
Envelope
A protective layer that envelopes usually consists of lipids, carbs, and proteins
Spikes
Protrusions, sometimes for attachment
Lysogenic cycle
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
Smallpox(Variola)
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
Poliovirus
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
Lyssavirus(Rabies)
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
Herpes simplex
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
Lentivirus(HIV)
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)
HIV Treatment
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)
Oncogenes
Genes that when are over active, and can transform normal cells into cancerous cells
Oncogenic viruses
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
DNA Oncogenic viruses(names)
- Adenoviridae
- Herpesviridae
– Epstein-Barr virus - Poxviridae
- Papovaviridae
– Human papillomavirus (cervical and anal cancers) - Hepadnaviridae
– Hepatitis B virus(liver cancer)
Persistent Infection
A persistent viral infection occurs gradually over a
long period; is generally fatal
– Subacute sclerosing panencephalitis (measles
virus)
Latent Viral Infection
Latent virus remains in asymptomatic host cell for
long periods
– May reactivate due to changes in immunity
§ Cold sores, shingles
Prions
• Proteinaceous Infectious particle
• Inherited and transmissible by
ingestion, transplant, and surgical
instruments
Prions chemical identity
• PrPC: normal cellular prion protein, on the cell surface
• PrPSc: scrapie protein; accumulates in brain cells,
forming plaques
