Viruses general info from book Flashcards
Essential viral components
Protein capsid, composed of capsomers
Nucleic acid, either DNA or RNA, never both
Lipid bilayer envelope in some.
General RNA virus characteristics
Most are:
Single stranded (about equal are poisitive or negative stranded) (just like RNA is usually single stranded)
Enveloped
Helical capsid
Replicate in cytoplasm
General DNA virus characteristics.
Most are:
Double stranded (DNA usually is) Icosahedral (20 sided die) symmetry Replicate in the nucleus
Mnemonic for the DNA virsus
HHAPPPY
Herpes Hepadna Adeno Papova Parvo Pox
DNA viruses that have envelopes
Herpes
Hepanda
Pox
DNA viruses that are naked/non-enveloped
PAP
PAPova
Adeno
Parvo
What RNA viruses are double stranded?
Reoviridae
What RNA viruses are naked/non-enveloped
PCR
Picorna
Calici
Reoviridae
What RNA viruses have icosahedral capsids
Reo Picorna Toga FFlavi Calici
What RNA viruses replicate in the nucleus
Retro and Orthomyxo
What are the Positive stranded RNA viruses?
“The CALCIfied old Emperor PICO is wearing his CROWN and RETRO TOGA and eating FLAVorful foods.
Calici Pico Corona Toga Flavi Retroviridae
What are the Negative stranded RNA viruses?
Orthologist Pete’s Rabid dog Filo fights Paul Bunyon in the Arena
Orthomyxo Paramyxo Rhabdo Filo Bunya Arenaviridae
What are the steps for viruses to enter a cell and reproduce?
1) Adsorption and Penetration
2) Uncoating
3) Synthesis and assembly of viral products
4) Release of virions from the cell (lysis, exocytosis, budding)
How does the transcription phase differ between RNA and DNA viruses?
DNA viruses are more complex usually, and their transcription phase is divided into three phases instead of all at once.
DNA viral transcription
Immediate early phase
Early phase
Late phase
In the immediate and Early phase, the mRNA and proteins neccessary to replicate the bacterial DNA is transcribed,
In the late phase structural proteins for the capsid are transcribed, off of replicated DNA strands.
Virus definition
A very small, non-cellular infectious agent that can only replicate inside of living, susceptible cells.
The smallest infectious agent possessing coding genes.
Virion definition
A single EXTRACELLULAR, INFECTIOUS virus
Vegetative Virus
An INTRACELLULAR, REPLICATIVE virus.
What is the size range of a viruses?
20-300 or 400nM
Describe viral taxonomy
It is based on structure and not evolution, and is thus called Artificially based.
Divided into DNA or RNA viruses then double stranded or single stranded then linear or circular RNA viruses farther divided by Positive or Negative Stranded.
Then by Capsid symmetry
Icosahedral/Cubic, Helical, or Complex
then Number of capsomers
then Diameter of the nucleocapsid
Finally,
is it enveloped or non-enveloped. (envelopes also called peplons).
What types of nucleic acids are possible in a virus
RNA or DNA
Single or double stranded
Circular or Linear
Continuous or Segmented
Positive or Negative stranded for RNA.
Positive stranded is ready to code, Negative stranded requires RNA-dependent RNA polymerase to be carried in the virion.
What are the possible characteristics of the virus capsid?
All are composed of capsomers. Many capsomers form an equilateral triangle to make one side of the capsid.
A single capsomer is a POLYMER of proteins and/or glycoproteins. Bound by specific, flexible, non-covalent bonds.
If the capsid and the nucleic acid is bound tightly, it is called a nucleocapsid.
Capsid shapes:
Rigid Helical, forms a rod shape
or
Flexible Helical, forms a sphere shape
Icosahedral/Cuboidal
Can also be rigid or more flexible, and then it is angular and icosahedral or more like a soccer ball.
Binal: with a helical tail and icosahedral head, seen just in bacteriophages
Complex: unique shapes like bullet shaped rhabdovirus or the brick-shaped smallpox.
What do these suffixes mean:
viridae
virinae
virus
Viridae: Family
Virinae: Subfamily
Virus: genus.
What are the ways a virus can be internalized to its host cell?
Non-enveloped viruses enter by internalization and endocytosis, usually by biding to a specific membrane protein on the host cell
Enveloped viruses also interact with a specific host protein, but then enter by fusion of their envelope with the host cells membrane.
What types of viral proteins are needed for replication?
Polymerase,
RNA- or DNA-dependent RNA- or DNA-polymerase
Nuclease
Ligase
What are the major types of viral proteins
Enzymes for replication: Polymerase, Nuclease, Ligase,
Precursor Proteins, which become Structural Protesin
Early Viral Proteins: Enzymes that repress host cell functions and redirect host cell organelles to viral replication, kinases, phosphatases
Late viral proteins: Inner and outer structural proteins of the virus
Inner structural proteins: bind viral nucleic acids
Outer structural proteins: capsid proteins that bind the virus host receptor,
Neuraminidase - cleaves sialic acid of glycoproteins to aid in cell lysis and virus release.
