Virus Structure and Function Flashcards
What is a virus?
Submicroscopic, obligate intracellular parasite that is not alive. They do not grow or undergo division.
What is the three part strategy for survival?
- They house genome in capsid.
- Genome contains all information for initiation and completion of infectious cycle.
- Establish relationship (benign or lethal) with host.
Define: Classical System
Viruses grouped according to their shared physical properties. Such as: Nature of genetic material (RNA and DNA) Symmetry of capsid Naked or Enveloped Dimensions of capsid
Define: Baltimore
Based on central Dogma: DNA to RNA to Protein (how do they produce RNA)
(+) strand mRNA
Translatable open reading frame. Ribosome-ready.
First key principle of viral genome
Small, finite number of nucleic acid copying strategies.
Second key principle of viral genome
Function of viral genome is to make mRNA.
What are the seven classes of viral genome configuration?
- dsDNA
- ssDNA
- gapped circular DNA
- dsRNA
- ss(+)RNA
- ss(-)RNA
- ss(+) RNA with DNA intermediate
What are the three functions of virion proteins?
- Protection of the genome
- Delivery of the genome
- Mediate interactions with the host
Name some characteristics of virus particles.
Symmetrical arrangement (helical or icosahedral), non-covalent, highly conserved, and identical bonds between identical subunits.
Which of the following symmetrical arrangements (helical or icosahedral) infect all forms of life?
Helical
What is the icosahedral capsid symmetry pattern?
Are they covalent or noncovalent interactions?
2-, 3-, 5-fold symmetry
Noncovalent
Enveloped virus membranes are made up of lipid bilayers and glycoproteins. Which is derived from the host and which is from the virus?
Glycoproteins are viral and lipid bilayer is derived from the host.
What are three sources of lipid bilayers for viral envelopes?
- Plasma membrane
- Golgi Apparatus
- Endoplasmic Reticulum
Name three roles of glycoproteins found in viral envelopes.
- Entry and host range determination
- Assembly and egress
- Evasion from the vertebrate immune system
Define eclipse period in viral growth.
Period of time after virus absorption where no infectious virus is detectable inside or outside of the cell.
Define latent period in viral growth.
The time it takes from the initiation of infection to the release of new infectious virus particles from the cell.
Name the events that occur in the latent period.
- Attachment
- Entry and Uncoating
- Gene expression
- Genome replication
- Assembly and egress
Give two examples of target receptors for viral attachment.
- Membrane proteins
2. Carbohydrates (less specific)
True or False: Entry of a virus is energy dependent.
Yes! The host cell must be metabolically active.
Define uncoating
Viral capsid is completely or partially removed and viral genome is exposed.
True or False- gapped DNA can be transcribed directly without any further modification.
FALSE. Gaps must be filled before genes can be transcribed.
Which enzyme transcribes viral DNA? Is it derived from host or virus?
RNA polymerase II and is host derived.
What enzyme is common to all RNA viruses?
RNA-dependent RNA polymerase (RdRp)
What pathway does the following genome need to take in order to be translated: (+) stranded RNA viruses
Can be directly translated
What pathway does the following genome need to take in order to be translated: (-) stranded RNA viruses
(-) stranded RNA viruses to (+) stranded RNA viruses
What pathway does the following genome need to take in order to be translated: dsDNA
(-) strand DNA to (+) stranded RNA viruses
What pathway does the following genome need to take in order to be translated: Retroviruses [(+) stranded RNA viruses with DNA intermediate]
(+) stranded RNA viruses to dsDNA to incorporation into host genome to (+) stranded RNA viruses
What enzyme is used for both production fo mRNA and the replication of RNA genomes?
RNA-dependent RNA polymerase (RdRp)
What enzyme allows for the copying of single stranded RNA genome into double stranded DNA?
Reverse transcriptase
Describe the two possible strategies dsDNA viruses use to replicate.
- Replication in the nucleus (dependent on cellular components)
- Replication in cytoplasm (independent of cellular components)
Where does ssDNA viral replication take place?
Inside the host nucleus
Does gapped DNA viruses need reverse transcriptase?
Yes.
What enzyme do RNA viruses use to replicate their genome?
RdRp
What are the two ways for icosahedral capsids package their genome?
- Capsid assembles around genome
2. Genome fed into capsid
How do naked viruses usually egress?
Lysis
How do enveloped viruses usually egress?
Budding
