Ch 6 Viruses And Othe Infectious Agents

Question 1

importance of viruses

Answer 1

major cause of disease
vital members of the aquatic ecosystem
can be used to destroy cancer cells
bacteriophages in human guts may regulate bacterial microbiome
important model organism

Question 2

viruses

Answer 2

infectious agents unique in their simple, acellular organization and pattern of multiplication

Question 3

extracellular viruses

Answer 3

inactive
cannot reproduce outside of living cells

Question 4

intracellular viruses

Answer 4

commandeer host cells and use them to synthesize viral components from which mature progeny viruses are assembled and released

Question 5

bacteriophages

Answer 5

virus that infect bacteria

Question 6

virion

Answer 6

mature virus particle
contains nucleocapsid - composed of nucleic acid, DNA or RNA, and a protein coat, capsid - which protects the genome
can be enveloped viruses (lipid membrane) or nonenveloped/naked

Question 7

capsid

Answer 7

• large macromolecule structures which serve as protein coat of virus
• made of protein subunits called protomers
• protect viral genetic material and aid in its transfer btw host cells
• constructed from many copies of one protein
• enveloped viruses require nucleocapsid proteins and extra proteins to anchor to the membrane
• helical, icosahedral, or complex

Question 8

helical capsid

Answer 8

shaped like hollow tubes with protein walls
- protomers self assemble into rigid tube
- size of capsid is influenced by protomers and genome

Question 9

icosahedral capsid

Answer 9

most efficient way to enclose a space
- a regular polyhedron with 20 equilateral triangular faces and 12 vertices
assemble in capsomers - ring or knob shaped units made of 5 or 6 protomers

Question 10

poxiviruses

Answer 10

largest of the animal viruses
complex interior and ovoid- to brick-shaped exterior

Question 11

binal symmetry

Answer 11

head resembles icosahedral, tail is helical

Question 12

envelope

Answer 12

outer membranous layer that surrounds a bacterial virus
in animal virus envelopes (lipids and carbs) usually arise from host cell plasma or organelle membranes

Question 13

peplomers/spiks

Answer 13

envelope proteins are coded for viral genes and often project from the envelope surface
involved in virion attachment to the host cell surface
can have enzymatic activity needed for entry or exit from host cell

Question 14

segmented genomes

Answer 14

genomes that consist of multiple pieces of RNA
usually all segments are enclosed by the same capsid

Question 15

five steps of viral multiplication

Answer 15

1. attachment (adsorption)
2. entry into the host
3. synthesis
4. assembly
5. virion release

Question 16

attachment (adsorption)

Answer 16

viruses require a host cell in which to multiple so a ligand (virion) attaches to a receptor (host)
- SARS CoV 2 spike protein is the viral ligand that attaches to the human receptor call A C E2
- in plants, no receptors found, instead damage of the host cell is required for entry
receptor determines host preference: tropism - viruses will bind to specific tissue receptors

Question 17

entry into the host

Answer 17

after attachment, the virus’s genome or entire nucleocapsid enters the cytoplasm
- in some cases, only the genome enters leaving the capsid attached to the outside of the cell

Question 18

3 methods of entry into the host

Answer 18

• fusion of the viral envelope with host cell’s plasma membrane
• endocytosis
• release of nucleic acid

Question 19

synthesis

Answer 19

this is the step that differs the most between viruses. genome dictates the events
- ds DNA follows typical synthesis
RNA viruses:
- virus must carry in or synthesize the proteins necessary to complete synthesis
- viral replication complexes - enclose machinery needed for genome replication
- tightly regulate gene expression and protein synthesis

Question 20

assembly

Answer 20

late proteins are involved
baseplate, tail fibers, and head components are all assembled separately

Question 21

virion release mechanisms

Answer 21

• host cell lysis (nonenveloped viruses)
• release by budding (enveloped viruses)

Question 22

budding release

Answer 22

virus-encoded proteins are incorporated into the membrane
then the nucleocapsid is simultaneously released and the enveloped formed by membrane budding
- may use host actin tails to propel through host membrane btw adjacent cells

Question 23

lysis

Answer 23

common for bacterial viruses and some nonenveloped animal viruses
involves the activity of viral proteins that puncture host plasma membranes and in the case of bacteriophages, degrade the host peptidoglycan

Question 24

virulent phage

Answer 24

begin to multiply immediately upon entering a bacterial host, and are released from the host by lysis

Question 25

temperate phage

Answer 25

have two reproductive options:
- reproduce like virulent phages
- remain within the host without destroying it

Question 26

lysogeny

Answer 26

relationship btw a temperate phage and its host

Question 27

prophage

Answer 27

form of virus that remain within its host
viral genome either integrated into the bacterial chromosome or free in the cytoplasm

Question 28

lysogenic bacteria/lysogens

Answer 28

infected bacteria
appear to be perfectly normal but
- cannot be reinfected by the same virus
- prophage is replicated and inherited within the genome of progeny cells

Question 29

lysogenic conversion

Answer 29

when a temperate phage changes the phenotype of its host
alteration in surface characteristics of the host
two advantages to lysogeny for virus
- allows viral nuclei acid to remain within a host
- high multiplicity of infection can occur but lysogeny allows host cell survival in few uninfected cells

Question 30

cytopathic effects (CPEs)

Answer 30

viruses that infect eukaryotic cells can cause microscopic or macroscopic degenerative changes or abnormalities in host cells and in tissues that are distinct from lysis

Question 31

animal viruses are usually cultivated by

Answer 31

inoculating suitable host animals or embryonated eggs
tissue (cell) cultures on monolayers of animal cells
cytopathic effects can be observed

Question 32

plant viruses are cultivated by

Answer 32

• plant tissue cultures, cultures of separated cells or plant protoplast cultures
• suitable whole plants: rub mixture of virus and an abrasive, may cause localized necrotic lesions or generalized symptoms of infection

Question 33

plaque assays

Answer 33

dilutions of virus samples made and plated with appropriate host cells
- results expressed as plaque-forming units

Question 34

viroids

Answer 34

infectious agents that consist only of RNA
- closed, circular ss RNA
- do not encode any proteins
- replication requires host cell
- cause plant diseases
- cause disease by triggering RNA silencing

Question 35

satellites

Answer 35

similar to viroids but nucleic acid gets enclosed in a capsid and they need a helper virus to replicate

Question 36

prions

Answer 36

made of only a single protein
cause a variety of neurodegenerative diseases in humans and animals
- scrapie, mad cow disease