Viruses (lecture 14) Flashcards
def
A virus is a very small, non-cellular parasite of cells.
Its genome, which is composed of either DNA or
RNA, is enclosed in a protein coat.
Are viruses living or nonliving?
Viruses belong to biology because they possess
genes, replicate, evolve, and are adapted to
particular hosts, biotic habitats, and ecological
niches. However…they are nonliving infectious
entities that can be said, at best, to lead a kind of
borrowed life.”
no metabolism
Virions
Virions are the virus delivery unit to new hosts
consist of the viral genome, the capsid, and often of
further accessory components
virion structure
envelope
matrix
genome
capsid:
-> protect the viral genome against inactivation.
recognize and attach to an appropriate host cell.
env virus?
advantage?
capsid containing viral genome without matrix and eveloping proteins
advantage:
resistance against environment
high variability»_space; evolutionary advantage (host specificity?)
The Baltimore classification
type of genome,
type of transcription,
type of replication.
DNA, RNA and RT Viruses
Viral lifecycle
- Attachment of a virion to a cell
- Entry into the cell
- Transcription of virus genes into mRNAs
- Translation of virus mRNAs into virus proteins
- Genome replication
- Assembly of the virus proteins and genomes into
virions - Exit of the virions from the cell
Attachment of a virion to a cell
receptor involvement
viruses attach to specific structures on host cells -> cell specificity
e.g. HIV - CD4
diff between env and nakes virus entering a cell
naked: only by endocytosis
env: by endocytosis and membrane fusion
have fusion proteins with hydrophobic regions
bicistronic mRNA
bicistronic mRNA contains code for the translation of two genes. In the same vein, polycistronic RNA contains code for multiple genes, while monocistronic RNA contains code for only one gene. polycistronic RNA occurs most often in prokaryotes– an example is the lac operon
translation of viral mRNA
transcription of viral genome can be done by viral or host RNA Pols
(RdRp are always viral)
DdRp can be both
RdDp always viral (RTs)
traslation is always done by host cell
translation machinery
However, many
mRNAs are bi-cistronic
HSV-1
env
ds DNA
HIV
env
ss + RNA
retrovirus
genome for gag, pol, env, and auxiliary proteins
Viruses are used in research and clinics
Phage typing of bacteria
Source of enzymes
Pesticide
Anti-bacterial agents
Anti-cancer agents
Gene vectors for protein production
Gene vectors for treatment of genetic diseases