Viruses Part II Flashcards
Chapter 13
What are the 3 types of viruses? (host cell type)
- Bacteriophage
- Plant Viruses
- Animal Viruses
What are primary cell lines?
Derived from tissues by enzymes (die after a couple of generations)
What are diploid cell lines?
Derived from human embryos (50-100 generations and then die)
What do viral genes code for? (3)
- capsid
- structural proteins
- enzymes
What does the virus use host cell enzymes for? (3)
- protein synthesis
- energy production
- ribosomes
Where do viruses replicate in?
ONLY inside a cell
What do viruses control when they invade a cell? (2)
- metabolic machinery
- replicative machinery
Describe the lytic cycle and give an example:
- host cell is lysed after viral replication
- T4 bacteriophage, Influenza Virus
Describe the lysogenic/latent cycle and give an example:
- host cell stays alive after replication
- viral genome integrated into host’s genome
- lambda bacteriophage, retroviruses
What are the steps of the viral replication cycle in animal viruses? (6)
- attachment/absorption
- penetration/entry
- uncoating
- biosynthesis
- maturation/assembly
- release
How do viral particles attach to a host cell?
Via specific receptors on the host cell
What are the attachment sites of viral particles made of?
Spikes or fibers that bind to receptors
Describe the attachment sites for naked viruses
nucleocapsid
Describe the attachment sites for enveloped viruses
envelope on spikes
How do naked viruses enter the host cell? (1)
- via receptor mediated endocytosis
How do enveloped viruses enter the host cell (2)?
- via receptor mediated endocytosis
- via fusion of envelope with host cell plasma membrane
What is uncoating?
Separation of nucleic acid from the protein capsid coat
What causes uncoating? (2)
- host lysosomal enzymes
- configurational changes in the capsid
Describe synthesis in viral replication
Virus takes over host’s biosynthetic “machinery”
What is produced in synthesis? (3)
- new viral nucleic acid molecules
- capsid proteins
- other viral components
Where do DNA viruses replicate?
- In the nucleus (except Poxviruses)
What enzyme do DNA viruses use?
- DNA dependent DNA polymerase
Where do RNA viruses replicate?
- In the cytoplasm (except Retroviruses and Orthomyxoviruses)
What enzyme do RNA viruses use?
- RNA dependent RNA polymerase
What happens in maturation/assembly? (2)
- capsomers assembled into capsids
- newly synthesized viral DNA inserted into capsids (forms new virions)
What happens in release for naked viruses? (2)
- released from host cell by lysing the cell
- host cell dies
What happens in release for enveloped viruses? (2)
- bud out of host cell
- acquire envelope from the host cell’s plasma membrane
How do retroviruses replicate? (3)
- through DNA intermediate
- double stranded DNA copy of the virus RNA made
- integrates into host genome
What enzyme is used in replication of retroviruses?
Reverse transcriptase
What is the simplified version of how retroviruses replicate?
RNA -> DNA -> integrates
List the steps of biosynthesis in retroviruses (4)
- RNA -> double stranded DNA
- DNA enters nucleus -> integrates
- DNA remains in host’s genome, PROVIRUS
- integrated DNA -> RNA -> proteins
How do retroviruses leave the host cell?
via budding
What is viral latency?
Time period where there is no replication of the viral genome
(T/F) Viruses cause disease during latency
False, they only cause disease when activated by different stimuli
Name two examples of viruses that remain latent until activation:
- HSV-1, Simplexvirus
- Chicken pox virus, Varicellovirus
Where is HSV-1 latent in?
Nerve cells
What does Varicellovirus cause after activation?
(Chicken pox) Shingles
What viruses cause cancer in humans? (2)
Human T-cell Lymphotropic Virus
- HTLV-1
- HTLV-2
What viruses cause leukemia?
Both retroviruses
What do both retroviruses cause?
Leukemia
What viruses cause cancer in animals? (3)
- Epstein-Barr Virus (EBV)
- Hepatitis B Virus (HBV)
- Human Papilloma Virus (HPV)
What is EBV associated with? (2)
- African Burkitt’s Lymphoma
- Nasopharyngeal carcinoma
What is HBV associated with? (1)
hepatocellular carcinoma (liver cancer)
What is HPV associated with? (1)
Cervical carcinoma
What are oncogenes?
Tumor genes
What is an oncogenic virus?
Virus that promotes tumor formation
Where are oncogenes derived from?
Normal cellular genes
Where do oncogenic viruses integrate in?
Host’s chromosome
What are prions?
Proteinaceous Infectious Particles: affect cellular proteins
What diseases are caused by prions? (4)
- Kuru
- Creuztfeld-Jacob Disease
- Mad Cow Disease (bovine spongiform encephalopathy)
- Scrapie (found in sheep)
What are common factors in diseases caused by prions? (2)
- all are neurological diseases (spongy appearance of the brain)
- all are fatal
What do prions do?
Convert normal proteins to an infectious abnormal protein
What is PrPc?
A normal cellular protein
What is PrPsc?
A scrapie protein, accumulates in brain cells + forms plaques
What are viroids?
Short pieces of naked RNA (no protein coat)
What do viroids cause?
Some plant diseases
What do viruses do?
Stops RNA from coding proteins
