Ch 13 Viruses Part 1 Flashcards
what are general characteristics of viruses
Non-living entities Not considered organisms Can infect organisms of all life-forms Obligate intracellular parasites Unable to reproduce outside of living cells
what do viruses contain
a single type of nucleic acid
a protein coat that surrounds the nucleic acid
where do viruses multiply and why
inside living cells, using the synthesizing machinery of the cell
what do viruses cause
synthesis of specialized structures that can transfer the viral nucleic acid to other cells.
describe viruses
Simple organization
DNA or RNA but not both (one exception)
Unable to reproduce outside of living cells
Obligate intracellular parasites
describe cellular organisms
Complex organization
Both DNA and RNA
Carry out cell division
Some are obligate intracellular parasites
Complete virus particle
virion
what does a virion consist of
Consists of nucleic acid surrounded by protein coat
what is the name of the protein coat
capsid
describe the capsid
composed of capsomeres
Protects genome and aids in transfer between host cells
virions can be what
naked or enveloped
describe naked vs enveloped
Naked – without envelope
Enveloped – surrounded by lipid membrane
these are membrane structures surrounding some viruses
viral envelopes
(spikes) are proteins in envelope and are virus specific
peplomers
Lipids and carbohydrates in envelope are usually derived from
host membranes
describe the viral genome
Contains only single type of nucleic acid
Either DNA or RNA (never both)
Can be linear or circular
Single-stranded or double-stranded
where does viral replication occur
Only multiply inside metabolizing cell
Use host machinery to support reproduction
every virus…
contains information to make viral proteins, assure replication and move in and out of host cells
what two phases to viruses live in
intracellular and extracellular
extracellular vs intracellular phases
Extracellular phase
Metabolically inert
Intracellular phase
Metabolically active
what are the morphological types of viruses
viruses have different shapes
Shaped like hollow tubes with protein walls
helical capsids
Regular polyhedron with 20 equilateral triangular faces and 12 vertices
Icosahedral Capsids
what are bacteriophages classified by
Based on two major criteria
Phage morphology
Nucleic acid properties
what was the oldest classification of viruses based on
symptomatology
what allows for grouping of viruses into families based on genomics and structure
DNA sequencing
group of viruses sharing the same genetic info and host range
viral species
what are viral enzymes entirely concerned with
replicating/processing viral nucleic acid
this shows the multiplication of viruses
one step growth curve
what are the five steps of the lytic cycle
1)attachment 2)penetration 3)biosynthesis 4)maturation 5)release
describe the attachment stage of the lytic cycle
attachment site on the virus attaches to a complementary receptor site on the bacterial cell chemical interaction(weak bonds are formed)
where are the complementary receptors sites
bacterial cell wall
describe the penetration stage of the lytic cycle
bacteriophage injects its DNA into the bacterium
phage lysozome
tail sheath of the phage contracts and tail is driven into cell wall
where does the capsid remain
outside the bacterial cell wall
what the bacteriophage’s tail releases
enzymes that breaks down a portion of the cell wall
phage lysozome
describe the biosynthesis stage of the lytic cycle
hose protein synthesis is stopped by virus induced degradation of the host DNA, viral proteins that interfere with transcription or repression of translation
period during viral multiplication when complete invective virions are not yet present
eclipse period
describe the maturation stage of the lytic cycle
bacteriophage DNA and capsids are assembled into complete virions
head is filled with phage DNA and attached to the tail
describe the release stage of the lytic cycle
release of virions from the hose cell
lysis
lysozyme
plasma membrane actually breaks open
lysis
encoded by phage gene and is synthesized within the cell
this causes bacterial cell wall to break down
newly produced bacteriophages are released and infect new cells
lysozyme
may proceed through a lytic cycle but are capable of incorporating their DNA into the host’s DNA to begin lysogenic
lysogenic phages
phage remains latent(inactive)
lysogeny
what are the stages of the lysogenic cycle
1)attachement 2)penetration 3) prophage 4)replicate prophage DNA 5)excision of DNA 6)lytic cycle
describe the prophage of lysogenic cycle
circle can recombine with and become part of the circular bacterial DNA
inserted phage=prophage
phage genes are turned off
describe the fourth stage of lysogenic cycle
replicates the prophage DNA
lysogeic bacterium produces normally
what are the three results of lysogeny
1) lysogenic cells are immune to reinfection by same phage
2) phage conversion
3) specialized trandsuction
host cell may exhibit new properties
phage conversion
this occurs when only certain bacterial genes can be transferred
specialized transduction
