Genetics of Viruses Flashcards
what does “obligate intracellular parasite” mean, and what does it describe?
viruses, cannot survive without living host cell
what do viruses depend on host cells for?
- amino acids and nucleotides
- protein-synthesis machinery
- energy (ATP)
what is the extracellular state of a virus, and its characteristics?
- virions
- metabolically inert
- no respiratory or biosynthetic functions
who is MRS GREN?
8 characteristics of living organisms
- movement
- respiration (metabolism)
- sensitivity
- growth
- reproduction
- excretion
- nutrition
what are the three arguments for viruses being living organisms?
- viruses can reproduce (in intracellular state)
- viruses can direct metabolic processes (in intracellular state)
- viral genomes can evolve (no single gene is shared by all viruses, viruses evolve w host and acquire their genes)
what are two arguments for viruses being non-living?
- viruses are not cells
- do not have protoplasm or organelles - viruses lack some living organism characteristics
- no metabolism
- no nutrition needed
- cannot make energy (ATP)
- not sensitive
- no growth
- no excretion
how do viruses challenge the cell theory?
- cells are smallest unit of life
- viruses have genetic material but no molecular machinery - cells arise from pre-existing
- can replicate but only in host cells - living organisms composed of cells
- viruses are acellular, no protoplasm or organelles
- metabolically inert, no resp or biosynthesis
what is the basic structure of a virus?
in all viruses:
- genome (DNA or RNA)
- capsid (protein coat)
in some viruses:
- envelope
- enzymes
describe the structure of the viral genome
- dna OR rna
- single OR double stranded
- linear OR circular
what are three types of viruses (classified by genetic material)?
((that u need to know))
- double-stranded DNA
- eg. T4 and lambda - negative sense single-stranded RNA
- genome is mRNA, immediately translated by host - single-stranded RNA-reverse transcriptase (RT) viruses
- reverse transcriptase (RNA to DNA) to produce DNA from viral RNA
what are two types of essential proteins coded for by viral genomes?
- regulatory: regulate host gene action
- structural: eg capsid protein
what is a capsid formed from?
capsomeres (identical protein subunits)
what are viral envelopes, and what is its function?
facilitating viral entry
what is the function of lysozyme, and which viruses contain it?
- penetrate bacterial cell wall, viral nucleic acid enters
- lyses host cell to release new virus later
- bacteriophages (T4 and lambda)
what if the function of neuraminidase, and what virus contains it?
- breaks down glycosidic bonds of glycoproteins/lipids of animal cell connective tissue
- aid in virus liberation
- influenza
what are the five general steps of reproduction of an enveloped virus?
- adsorption (attach to host)
- penetration (viral nucleic acid enter host cytoplasm)
- synthesis & replication (new viral components made by host cell machinery)
- assembly (new viruses assembled)
- release (new viruses leave)
what are examples of virulent and temperate phages?
virulent: T4 (lytic)
temperate: lambda (lysogenic)
describe the structure of a T4 phage
- head (with double-stranded DNA)
- tail (tail sheath, multiple tail fibres, base plate)
what is the function of tail fibre(s) in a virus, and what type of virus has how many each?
- allows phage to adsorb onto surface of bacterial host by binding to specific receptors on cell surface
- virulent / lytic / T4: multiple
- temperate / lysogenic / lambda: one
what is the function of a tail sheath in viruses, and in which viruses is it found?
- surrounds central tube
- contracts during penetration, thrusts central tube through host cell wall and membrane
- found in virulent bacteriophages
what is the function of a base plate in viruses?
- contacts host cell surface
- undergoes conformational change
- allows DNA to be extruded from head, through central tube into host cell
what are the types of nucleic acids found in T4, lambda, influenza, HIV?
- T4 AND lambda: double-stranded DNA
- influenza: eight segments of negative sense single-strand RNA
- HIV: two identical positive-sense single-stranded RNA (RT)
what are the reproductive cycles of virulent and temperate phages respectively?
lytic and lysogenic
what is the structure of the head of lambda bacteriophage?
5’-terminus of each DNA strand is single-stranded tail of 12 nucleotides long
important in prophage formation