Viruses

Question 1

What is the Lytic Cycle

Answer 1

Attachment: Phage attaches by tail
fibers to host cell
 Penetration: Phage lysozyme opens cell
wall; tail sheath contracts to force tail
core and DNA into cell
 Biosynthesis: Production of phage DNA
and proteins
 Maturation: Assembly of phage
particles
 Release: Phage lysozyme breaks cell
wall

Question 2

What is Lysogenic Phase

Answer 2

following penetration not all viruses enter
the lytic phase
 phage DNA inserted into host cell
chromosome
 inserted prophage DNA is latent (no new
virions made and host cell remains healthy)
as bacterium multiplies, so does virus

Question 3

Results of Lysogeny

Answer 3

 Cells immune to reinfection
 Cells exhibit new properties (phage
conversion)
 Specialized transduction can occur
◦ (bacterial genes transferred)

Question 4

Pathogenic Conversion

Two mechanism by which naive bug can acquire virulence factors

Answer 4

◦ Conjugation in gram negative bacteria

◦ Lysogenic conversion in viruses

Question 5

Important virulence factors are glycoprotein
spikes that contain two glycoproten
molecules

Answer 5

hemagglutinin (H)

neuraminidase (N)

Question 6

neuraminidase (N)

Answer 6

breaks down mucus of

respiratory tract

Question 7

hemagglutinin (H)

Answer 7

binds to host cell
receptors of nasal epithelium (lytic phase
leads to cell death of ciliated epithelial cells)

Question 8

Hemagglutinin

HA

Answer 8

spikes used
for attachment to
host cells/
recognition

Question 9

Neuraminidase

NA

Answer 9

spikes used
to release virus
from cell

Question 10

Antigenic drift

Answer 10

viral nucleic acids exhibit
frequent mutations that alter surface antigens
(aids in evasion of immune responses),

Question 11

Antigenic shift

Answer 11

swapping of genes from different

strains increases virulence

Question 12

Differences between bacteriophages and Animal Viruses

Answer 12

Lysogeny replaced by latency, slow infections,
cancer
 Enveloped viruses bud out, non enveloped
rupture plasma membrane

Question 13

Adsorption

Answer 13

attaches to host cell receptors via
spikes/capsid protein

 presence of host cell receptor required for
invasion

Question 14

Penetration

Answer 14

a) endocytosis (naked or enveloped) – naked virus
must penetrate in this fashion (except phage)
b) fusion of envelope (enveloped only) with host
cell membrane

Question 15

Uncoating

Answer 15

– envelope/capsid degraded and

nucleic acid liberated to cytoplasm

Question 16

Synthesis

Answer 16

host cell enzymes (incuding
ribosomes) are hijacked to make more nucleic
acid (replication) and capsomers (protein
synthesis)

Question 17

Assembly

Answer 17

capsid is constructed and nucleic acid
inserted (nucleocapsid formed)
 in enveloped viruses, spikes are inserted into
cell membrane to be picked up during the release
phase

Question 18

Release

Answer 18

a) nonenveloped – lysis (rupture) of cell releases
virions
b) enveloped – bud from surface and acquire
envelope

Question 19

Prions

Answer 19

Noncellular infectious agents
 Protein only, no nucleic acid
 multiply by converting normal prion protein
to pathogenic form
 are transmissible (sometimes across
species)
 cause chronic neurodegenerative diseases
(called encephalopathies) in humans and
animals
 long latency from infection to first
symptoms

Question 20

Viruses

Answer 20

Outside of host cell  virus inactive
 Inside of host cell  active or inactive
 20-200 nm
 standard sterilization filter is 0.22 m (220
nm)
a) bacteria (larger than 0.22 m) are
retained
b) viruses (filterable) are not

Question 21

capsid

Answer 21

protein shell

Question 22

nucleocapsid

Answer 22

nucleic acid + capsid

Question 23

virion

Answer 23

fully formed virus capable of infecting

host cell

Question 24

naked virus

Answer 24

slang for a nonenveloped virus

Question 25

Virion Structure

Answer 25

Nucleic acid ◦ DNA or RNA  Capsid ◦ Capsomeres  Envelope  Spikes

Question 26

formation of viral envelope from host cell

Answer 26

 host membrane proteins are replaced with
glycoprotein spikes encoded by viral nucleic acid
  spikes used for recognition and attachment to
host cells

Question 27

Capsid/envelope functions

Answer 27

protection (may withstand low pH of stomach and
digestive enzymes, e.g.)
 aid in penetration of virus into host cell
 provide markers for recognition by cells of
immune system

Question 28

Cytopathic effects

Answer 28

refers to structural changes in host cells that are caused by viral invasion.

Question 29

Serological tests

Answer 29

◦ Detect antibodies against viruses in a patient
◦ Use antibodies to identify viruses in neutralization
tests, viral hemagglutination, and Western blot

Question 30

 Nucleic acids

Answer 30

◦ RFLPs (restriction fragment length poymorphism)

◦ PCR (polymerase chain reaction)

Question 31

Bacteriophage

Answer 31

Viruses that infect bacteria
Phage multiplication cycle
lytic phase or lysogenic phase
Induction: switch from
lysogenic to lytic phase

Question 32

Lytic cycle

Answer 32

Phage causes lysis and death of host cell.

Question 33

Lysogenic cycle

Answer 33

Prophage DNA incorporated in host DNA.