Unit 6 Flashcards
what is a virus?
infectious agent made up of nucleic acid (DNA/RNA) wrapped in protein coat (capsid)
what kind of parasite is a virus?
obligate intracellular
what are the hosts of viruses?
bacteria
animal
plants
what are the two essential components of viruses?
- genetic material (DNA/RNA)
- protective protein coat called capsid
what are the characteristics of viruses?
- no nucleus
- no organelles
- no cytoplasm/cell membrane
- doesn’t belong to any kingdoms
- either naked or enveloped
how to viruses exist?
hijacking the cellular machinery of another living thing to reproduce by injecting its genetic material into a host cell
what is on the outside of viruses?
outer envelope derived from host cell with specific spikes of protein (H and N spikes of influenza)
what do the spikes on the envelope do?
aids in attachment and makes them sensitive to chemical actions of disinfectants
what are the three major scenarios of origin of viruses?
- virus early hypothesis
- regression hypothesis
- escaped genes hypothesis
what is the virus early hypothesis?
- at the beginning there were replicative elements (preceding early life forms)
- viruses evolved from ancestor
what is the regression hypothesis?
- degeneration of cells was basis for viral rise
- later acquired parasitic lifestyle
what is the escaped genes hypothesis?
- cellular genes simply acquired ability for selfish replication and spreading
what is the structure of viruses?
- contain nucleocapsid composed of nucleic acids and protein coat
what is the virion envelope?
- outer, flexible, membranous layer
- animal virus envelope originate from host cell plasma or nuclear membranes
what are the characteristics of the envelope?
- viral ID
- enzymatic activity
- play role in nucleic acid replication
why is it accepted that variety of virions have enzymes?
reverse transcriptase in HIV
how do viruses recognize cells it can infect?
matching its surface marker with receptor site on a cell
does rabies only attack brain or nervous cells?
yes
are viruses bigger than bacteria?
no smaller
what are the kinds of symmetry in viruses?
- helical
- icosahedral
- complex (bacteriophage)
RNA virus genome
~ 70% viruses are RNA virus
- inside the capsid it can have either single strand or double stranded RNA virus
DNA virus genome
- linear double strand DNA is found as genome
- some contain circular DNA genome and single strand
what is the virus replication cycle?
- attachment
- penetration or viral entry
- synthesis
- assembly
- release
describe the virus replication cycle
- virion attaches to the correct host cell
- virus or viral nucleic acid gains entrance into cell
- viral nucleic acid and proteins copies are manufactured by cells’ machinery
- viruses are produced from viral components
- newly formed virions are released from cell
virus attachement
specific receptor attachment varies between naked and enveloped virus
- key-lock system
penetration or viral entry
- fusion of viral envelope with host membrane- nucleocapsid enters
- endocytosis in vesicle- endosome aids in viral uncoating
- injection of nucleic acid
synthesis
- viral nucleic acid and proteins copies are manufactured by cells’ machinery
- virus cannot reproduce by itself - must invade a host cell and take over cell activities, eventually causing destruction of cell and killing it
- virus enters cell, makes copies of itself and causes cell to burst releasing more viruses
- viral reproduction takes place by lytic infection or through lysogenic infection
reproduction of virus
- lytic infection
- lysogenic infection
lytic infection
virus enters host cell, makes copy of itself, causes cell to burst or lyse
lysogenic infection
- virus doesn’t let host cell to lyse away
- can remain dormant
- viral DNA gets integrated with host cell DNA where it gets copies with host cell DNA
- viral DNA gets multiplied with host cell DNA and each daughter cell created is infected with DNA
- under stress = lytic cell
virus outside host cell
- viruses can live outside of body depending on moisture and temp
- live longer on water-resistant surfaces
- cold virus can sometimes survive on indoor surfaces for days but ability to cause infection drops dramatically
- flu can survive in air for hours esp at lower temp
- enteric survive for weeks on surface if suitable
can viruses be treated with antibiotics?
no
t or f: viruses disrupt the body’s normal equilibrium/balance
true
genetic engineering
harmless virus carries good genes into cells
phage therapy
bacteriophage along with antibiotics against antibiotic resistant bacteria
animal viruses
avian flu
- most don’t infect humans
plant viruses
- tobacco mosaic virus (TMV) causes mottled browning of tobacco leaves
- infects other crops- tomatoes
bacteriophages
- virus that infects and replicates within bacterium, attaches itself and infects host cell
- enzymes destroy bacterial cell wall from outside and inside by hydrolyzing carbs and protein components
- extensive gene exchange in phages
- absence of homology at nucleotide level between phages
- small number of different virion structures in nature
bacteriophage T4
- 1 of 7 E. coli phage
- models for study
divergent evolution
- viruses share common ancestor
- maintained basic architecture of structural proteins
- diverged beyond detectable levels of homology
convergent evolution
- viruses do not share common ancestor
- simply converged toward strucutre that is optimal to build infectious particle (virion)
what did both types of evolution lead to?
- single common trait that helps them survive in specific environment (host cell)
which hypothesis was most likely to be adopted?
divergent
- accumulation of similar structural characteristics
- common ancestor
what are the similarities between domains?
- tectividae phage PRD1 major capsid protein fold highly similar to that of archaeal virus STIV134 and mammalian adenoviruses
- relationship exists between tailed double-stranded DNA phages, the archaeal virus HSTV-1 and herpesviruses
- similarity of phages phi6 and phi8 with eukaryotic viruses
viral sunt in soils
- performed viral lysis of soil microbial community
- nutrient and dynamic of microbes in soil examination after viral lysis
- dissolved organic matter evaluated
does viral lysis of bacterial cells in soil affects soil nutritive characteristics?
- at two different temps nutrient limitation was removed after viral lysis
- viral lysis increased DOM
- microbes survived re-utilize DOM
- increased metabolic activity in soil
RNA hypothesis
- widely accepted
- only molecule to do reverse transcription from DNA
- descended of RNA world inhabitants are RNA viruses whose replication relies on RNA dependents RNA polymerase (RdRp)
what is RdRp?
- only universally conserved hallmark protein in RNA viruses
- key for reconstruction viral evolutionary history
- typical viral hallmark, no homolog with same enzymatic activity
what’s another viral hallmark?
reverse transcriptase
- copies DNA from RNA
