Ch 11 Viruses Flashcards
viruses
*some cause cancer *can be transmitted from person to person *comes from the latin word for poison *infectious agents too small to be seen by microscope *have no nucleus, organelles, or cytoplasm *display properties of living organisms when they invade host cells *can replicate or multiply only in living host cells.
obligate intracellular parasites
can replicate or multiply only in a living host cell.
virus composed of
*nucleic acid core *protein coat called capsid
*some have surrounding lipid bilayer membrane called envelope
viron
complete virus particle, including its envelope
components of virus- Nucleic Acid
*viruses use their genetic info (genome) to replicate themselves in host cells
*results in disruption of hosts cellular activities or death of the host
*can be single stranded or double stranded, linear, circular, or segmented (existing in several fragments)
capsid
*nucleic acid of an individual viron is enclosed by capsid
*protects nucleic acid and determines the shape of the virus
*plays key role in the attachment of some viruses to host cells
envelope
*bilayer membrane outside their capsid
*envelope is acquired after they are assembled in host cell
*viruses without envelope are known as naked, or non-enveloped
*made of combination of lipids, proteins, and carbohydrates
* projections (spikes) may extend from the viral envelope.
spike proteins
*some viruses have surface projections (glycoproteins)
*serve as attachment sites to specific receptor sites on host surfaces
size and shapes of viruses
*too small to be seen with light microscope
*largest are between 1,200nm - 1,500nm.
*smallest are less than 30nm in diameter
*many bacteriophages (viruses that infect bacteria) have complex shapes that incorporate specialized structures such as heads, tails, and tail fibers.
origins of viruses
*viruses differ from cellular microbes
*free viruses are incapable of reproducing
*must infect host to use hosts machinery to copy & transcribe viral genetic material
*cannot definitively say whether viruses are living or non-living
*over 40,000 strains of viruses known
classification of viruses
*initially classified by the type of host infected or by type of host structures infected.
* later classified by structure of nucleic acids, method of replication, host range, chemical & physical characteristics.
*family is the highest taxonomic category used.
nucleic acid classification
*viruses distinguished by their nuclic acid content as either DNA or RNA viruses
*RNA viruses can be single or double stranded (most single)
RNA viruses
*can be either single or double stranded
*most are single stranded
*because eukaryotic cells dont have the enzymoe to copy viral RNA molecules, RNA viruses must carry the enzymes or have the genes for the enzyme in their genome
positive sense RNA
*during infection the RNA acts like mRNA
*can be translated by the hosts ribosomes.
negative sense RNA
*RNA acts like a template during transcription to make a complementary +sense mRNA.
*then that strand is translated by host ribosomes.
*in order to perform transcription step, -sense RNA must carry a RNA polymerase within the viron
