Viruses Flashcards
Alex Lecture 2 (24 cards)
how are viruses imaged?
using electron microscopy.
electron beams to look at structures
what are polymorphic viruses?
viruses with no defined shape
what is a bacteriophage?
a virus that infects and replicates within bacteria
why are all viruses described as “obligate” intracellular parasites?
obligate = cannot REPRODUCE outside of host cell
vs facultative intracellular parasites can live / reproduce either inside or outside of cells
key features of viruses
- evolve rapidly, highly error prone
- hijack the host’s synthetic/energy/transport systems
also: diversity of morphology (shape)
what is the Baltimore Classification of viruses based on? explain the classes.
how viruses produce mRNA (necessary to hijack host’s translation machinery to produce viral proteins).
type: DNA or RNA
strand: Single or Double
Polarity: + or - for ssRNA
replication strategy
–> 7 classes
what is the difference between positive and negative sense RNA viruses?
+ve sense: orientation is same sense as mRNA, can be directly translated.
-ve sense: complementary to mRNA, must first be TRANSCRIBED to +RNA using RNA dependent RNA polymerase before translation
approximately spherical viruses are described as what shape?
icosahedral (20 faces)
what does a pleomorphic mean? (shape)
pleomorphic = varying morphology, varied shapes and sizes due to lipid envelope
define subunit (of a virus)
single folded polypeptide chains (ie protein molecule) making up part of the viral capsid
define structural unit (virus)
protomer = repeating assembly of subunits, forming the basic building block of the capsid
define capsid
the protein shell that encloses the viral genome, made up by assembling protomers (which are made up of subunits) into capsomers
define nucleocapsid
the viral genome + the capsid
can be the whole virion for non-enveloped viruses.
what does the concept of “Genetic economy” refer to in general?
viruses, due to limited genomic space, adopt a design that minimises the number of protein subunits needed
ie. max efficiency in protein product/structure
what does the Caspar-Klug theory refer to?
a construction theory, building on the idea of genetic economy.
allows for the construction of large, complex capsids from a small number of protein subunits, using triangulation numbers to describe the organisation of subunits on the capsid surface
name the give key stages of the virus replication cycle (ie. how viruses interact with cells)
- Absorption / Attachment
- Penetration (endocytosis), viral DNA enters host cell
- Eclipse phase (biosynthesis of viral proteins)
- Assembly / maturation
- Virion release / exocytosis
DRAW DIAGRAM
why is understanding the virus replication cycle important for biotech?
the replication offers lots of opportunity to develop antiviral strategies (literally possible to inhibit at every step)
how do viruses attach themselves to host cells?
interactions between viral proteins on the envelope/capsid and receptors on the host cell membrane (eg. GPCRs)
HIGHLY SPECIFIC binding – viruses can only infect cells with the appropriate receptor
two methods of virion release (final stage of replication cycle)
lytic or non-lytic (virion particles can be exocytosed)
what are prodrugs?
a compound with little/no pharmacological activity, until metabolised in the body it converts to the active drug
eg. being converted to a triphosphate by some enzyme –> active form
how can antiviral drugs use virus specific kinases?
use these kinases to selectively activate only in infected cells
ie. prodrug activated by virus specific kinase by phosphorylation
why are a cocktail of drugs often used to treat viral infections?
- viruses mutate rapidly, would evolve resistance to one type of drug quickly
- complete viral suppression - different drugs block multiple steps
eg. HAART, to treat HIV
what technology derived from viruses may be a viable antibody alternative?
phage therapy
