Cellular Genetics: Virus Quiz Flashcards
What is a virus?
An obligate, intracellular parasite made up of nucleic acid (DNA or RNA) and protein, sometimes surrounded by a membrane
Viruses lack the ability to acquire energy ____ .
Independently
How do viruses differ from each other?
In size, structure, genome type, host type, transmission
What are the 2 unifying characteristics of viruses?
- All must make their own ribosomes that can be translated by the host (no viruses contain their own ribosomes)
- All are obligate, intracellular parasites that can’t function or replicate outside of a cell
What is the main difference between viruses and bacteria?
Viruses do not grow and divide and do not have the metabolic properties of bacteria
What are two functions of the structural proteins found on viruses?
- Protection of genome
- Delivery of the genome
What does it mean that virus particles are metastable?
- Must protect the genome (stable)
- Must come apart on the infection (unstable)
What was the first ever virus to be discovered and what did it teach us?
- TMV helped us understand that virus particles form spontaneously from subunits without any extra information
What is the implication of these self-assembling virus particles?
- Particle is the most energetically favorable structure of the components
- Gives the particle its inherent stability and is an important feature of virions.
What is a zoonotic virus?
One that is transmitted form an animal to human.
What is a vector?
An intermediate organism through which viruses are transmitted from one type of host to another.
What is a virome?
The entire population of viruses associated with the human body
What are the 3 virus particle types in the world of viruses?
Helical, icosahedral, and complex
Identify the 3 types of axis symmetry that govern the rules of icosahedral symmetry.
- An axis of two-fold rotational symmetry through the center of each edge.
- An axis of three-fold “ “ of each face.
- An axis of five-fold “ “ of each corner (vertex).
What is the complex virus shape?
Bacteriophage
What is the helical virus shape?
Hollow, cylindrical capsid
What is the icosahedral virus shape?
Polyhedral capsid with 20 triangular facets
Distinguish among subunit, structural unit, capsid, nucleocapsid, and envelope.
Capsids are made up of repeated structural units, and structural units are made up of redundant subunits. The capsid is an effective barrier that when coated in a lipid envelope, together becomes the nucleocapsid. Viruses can either have or not have an envelope.
What is a subunit? What is another name for it?
- A single folded polypeptide chain
- Also known as capsomere
What is a structural unit?
One or more subunits from which capsids or nucleocapsids are built.
What is a virion?
Infectious virus particle
What is the capsid?
Protein shell surrounding genome
What are some of the enzymes you can find in the capsid?
- RNA-dependent RNA polymerase (enzyme that uses RNA as a template to produce RNA)
- Reverse transcriptase (enzyme that uses RNA as a template for DNA synthesis)
- Integrase (enzyme responsible for integrating viral DNA into host cell’s DNA)
- Protease (enzyme that breaks down and modifies proteins)
What does IRES stand for?
Internal ribosome entry site
What does UTR stand for?
Untranslated region
What is the nucleocapsid? When is it used?
- Nucleic acid core and protein assembly
- Used when is a discrete substructure
What is the envelope?
- Host cell derived lipid bi-layer
- Outermost coating that surrounds the capsid and contains glycoproteins
What does it mean for a cell to be susceptible?
A cell has a functional receptor for a given virus (may or may not to be able to support viral replication)
What does it mean for a cell to be resistant?
A cell has no receptor (may or may not be competent to support viral replication)
What does it mean for a cell to be permissive?
A cell has the capacity to replicate virus (may or may not be susceptible)
What is required of a host cell to take up a virus particle AND replicate it?
Must be both susceptible AND permissive
What are the basic steps of the replication cycle?
- Attachment and entry into the host cell
- Un-coating or release of genome
- Translation of viral proteins
- Replication of viral genome
- Assembly of new virus particles
- Release from cell
What happens in attachment and entry?
- Proteins on exterior of virus adhere to host cell membrane (absorption)
- Attach to specific receptor molecules
What are the two basic methods of uncoating?
- Fusion at the plasma membrane
- Within endosomes (endocytosis or engulfment)
When does assembly begin?
When genome is copied AND viral proteins are synthesized (the capsid)
What happens at assembly that only applies to enveloped viruses?
Only for enveloped viruses are there additional steps: acquisition of an envelope and maturation of virus particles
Where do assembly happen?
Nucleus or cytoplasm
How do enveloped and nonenveloped viruses exit the host cell?
- Enveloped viruses exit through budding
- Nonenveloped viruses exit through exocytosis, lysis (viral infected cell bursts and releases viruses) and death of cells
Do animal viruses need receptors? Fungi and plant viruses?
- Animal viruses need receptors
- Fungi and plant viruses don’t. They enter cells by damage/openings.
What are the receptors for influenza?
HA (hemagglutinin) binds to oligosaccharides
What are the two receptors for HIV-1? Where are they found OR what is their function?
- CD4 found on helper T-cells
- CCR5 is necessary to trigger a fusion of the membrane
What are the receptors for SARS CoV-2? What is their function?
- ACE (angiotensin converting enzyme)
- Plays a central role in controlling blood pressure through the regulation of fluids in the body
What are (+) RNA viruses?
Genome can be directly translated to functional proteins by the ribosomes of the host cell
What are (-) RNA viruses?
- Require synthesis of an RNA strand complementary to the (+) RNA strand
- Must carry an RNA replicase in virions to make complementary strand
