Virus As Infectious Agents Flashcards
What are viruses?
An infectious agent which consists of nucleic acid contained within a protective protein coat that protects its genetic being
Infect prokaryotes and eukaryotes
Difference between bacteria and virus
Viruses are not affected by antibiotics
Viruses are not “alive” : CANNOT replicate outwith a cellular environment – produced by assembly of preformed components : ‘obligate intracellular parasites’ : lack critical components (eg energy, machinery for self sufficient propagation)
Vision (what are the virus particle structures)
Genome (virus nuclei acid) + capsid (virus-encoded proteins) make up nucleocaspid
Some viruses also have envelope (lipid belayer derived from cellular membranes)
2 types of virus symmetry shapes
Icosahedral
Helical
Describe properties of icosahedral shape of viruses
20 faces each face an equilateral triangle
axes of 2-, 3- and 5-fold rotational symmetry
Capsomer structure enclosing maximum volume
Formed from repeated subunits
Some are enveloped
Describe properties of helical shape of virus
Coiled, telephone cord-like appearance
Provides protection for genome without need to encode multiple capsid proteins
All helical symmetry viruses are enveloped
What is advantageous about a virus having symmetry?
Saves genetic space; few genes copied MANY times
Function of the envelope in a virus
Protects genome from being harmed which would destroy its ability to make templates of itself
Facilitates binding & entry of viruses into cells and release of genome in cell
Proteins/structures within envelope/capsid of virus are a major target of…
Immune response
What are virus genomes
-Genetic “heritage”, biological material that they need to be able to replicate
-Codes for virus functions proteins) required for replication and interaction with host
Virus genome properties
-made of…
-single or double stranded?
-shape? Segments?
-size
-DNA or RNA (never both)
-single or double
-linear or circular
-segmented or non segmented
-2-300kbp
List the virus classification in order
Order—>family—>subfamily—>genus—>common species name
What is viruses aim?
To reproduce its genetic material
To multiply viruses must…
Infect cells
Do all viruses exploit host cell in the same way to replicate?
Nah
Name the steps of virus replication
1a) attachment
1b) penetration
1c) uncoating
2) gene expression and genome replication
3) assembly and exit
Describe each step of virus replication
1a) attachment: virus anti receptors interact with cellular receptors
1b) penetration: receptor mediated endocytosis—> fusion with lipid bilayer of plasma membrane
1c) uncoating: partial/total disruption of virus particle to facilitate gene expression- can occur in cytoplasm or nucleus depending on site of replication
2) gene expression and genome replication: replicate in different cellular compartments depending on what type it is; most DNA viruses replicate in nucleus (not pox), most RNA viruses explicate in cytoplasm (not retro, orthodomy)
3) assembly and exit:exit by;
-simple release
-release by budding
-release by exocytosis which damages cell causing it to lyse
