Chapter 8: Viruses

Question 1

Virus

Answer 1

genetic element that cannot replicate independently of a living (host) cell

Question 2

Virus particle

Answer 2

virion
extracellular form of a virus
exists outside host and facilitates transmission from one host cell to another

Question 3

infection

Answer 3

entry of viral DNA into host cell

Question 4

Capsid

Answer 4

the protein shell that surrounds the genome of a virus particle

Question 5

Naked virus

Answer 5

have no other layers than a capsid
- ie most bacterial viruses

Question 6

Enveloped virus

Answer 6

have outer layer consisting of a phospholipid bilayer (from host cell membrane) and viral proteins
- ie many animal viruses

Question 7

Nucleocapsid

Answer 7

nucleic acid + protein capsid

Question 8

virulent infection

Answer 8

lytic
- replicates and destroys host

Question 9

lysogenic infection

Answer 9

host cell genetically altered because viral genome becomes part of host genome

Question 10

capsomere

Answer 10

individual protein molecules arranged in a precise and highly repetitive pattern around the nucleic acid making up the capsid

Question 11

icosahedral

Answer 11

spherical viruses
most efficient arrangement of subunits in a closed shell
requires fewest capsomeres
- ie. Ebola, human papillomavirus

Question 12

Helical

Answer 12

rod-shaped viruses
length of virus determined by length of nucleic acid
width of virus determined by size and packaging of capsomeres
- ie. tobacco mosaic virus, Human rhinovirus

Question 13

complex

Answer 13

ie. bacteriophage

Question 14

lysozyme

Answer 14

makes holes in cell wall to allow nucleic acid entry
also lyses bacterial cell to release new virions

Question 15

neuraminidases

Answer 15

destroy glycoproteins and glycolipids
allows liberation of viruses from cell

Question 16

nucleic acid polymerases

Answer 16

RNA-replicases + reverse transcriptase

Question 17

Phases of viral replication in a permissive host

Answer 17

attachment - penetration - synthesis - assembly - release

Question 18

virus replication growth curve:

Answer 18

one-step growth curve
- numbers increase when cell bursts

Question 19

Eclipse

Answer 19

genome replicated and proteins translated

Question 20

maturation

Answer 20

packaging of nucleic acids in capsids

Question 21

latent period

Answer 21

eclipse + maturation

Question 22

release

Answer 22

cell lysis, budding, or excretion

Question 23

burst size

Answer 23

number of virions released

Question 24

lawns

Answer 24

hosts in liquid medium or spread on agar and inoculated with viruses
- best for bacterial viruses

Question 25

tissue culture

Answer 25

animal organ in culture medium - used for animal viruses

Question 26

titer

Answer 26

number of infectious units per volume

Question 27

plaque assay

Answer 27

plaques are clear zones that develop on lawns of host cells where successful viral infection occurs (where cells are being lysed)

Question 28

plating efficiency

Answer 28

number of plaque-forming units is always lower than direct counts by electron microscopy - efficiency of infection is usually much lower than 100%

Question 29

Attachment

Answer 29

requires complementary receptors on the surface of a susceptible host for its infecting virus - proteins, carbs, glycoproteins, lipids, lipoproteins, or other cell structures

Question 30

penetration

Answer 30

capsid left outside cell, viral genome and viral proteins (some viruses) enter host

Question 31

T4 penetration

Answer 31

-attach via tail fibers interactions with E. coli LPS layer -fibers retract and tail pins contact cell wall -T4 lysozyme forms small pore in peptidoglycan -tail sheath contracts, viral DNA enters cytoplasm -capsid stays outside

Question 32

restriction endonucleases

Answer 32

enzymes that cleave foreign DNA at specific sites -specific for dsDNA (ssDNA/RNA unaffected)

Question 33

modification

Answer 33

modification of cells own DNA at restriction enzyme recognition sites prevents cleavage of own DNA - ie base substitution

Question 34

circular permutation

Answer 34

same genes arranged in different orders - features of tmany virus genomes

Question 35

terminally redundant

Answer 35

some DNA sequences duplicated on both ends

Question 36

early proteins

Answer 36

enzymes needed for DNA replication and transcription

Question 37

middle and late proteins

Answer 37

head and tail proteins and enzymes required to liberate mature phage particles

Question 38

virulent

Answer 38

viruses always lyse and kill host after infection

Question 39

temperate

Answer 39

viruses replicate their genome in tandem with host genome and without killing the host, establishing long-term, stable relationship

Question 40

lysogen

Answer 40

host cell that harbors temperate virus

Question 41

lysogeny

Answer 41

most viral genes are not transcribed - viral genome is replicated with host chromosome and passed to daughter cells

Question 42

prophage

Answer 42

viral DNA

Question 43

transduction

Answer 43

packaging of host chromosomal genes and transfer to new host

Question 44

cl protein

Answer 44

the lambda repressor - causes repression of lambda lytic events

Question 45

cro repressor

Answer 45

controls activation of lytic events

Question 46

latent infection

Answer 46

viral DNA exists in host genome and virions are not produced; host cell is unharmed unless/until virulence is triggered

Question 47

persistent infection

Answer 47

release of virions from host cell by budding does not result in cell lysis - infected cell remains alive and continues to produce virus

Question 48

transformation

Answer 48

conversion of normal cell into tumor cell

Question 49

retroviruses

Answer 49

RNA virus that replicate through a DNA intermediate -ie HIV

Question 50

gag

Answer 50

encode structural proteins in retrovirus

Question 51

pol

Answer 51

encode reverse transcriptase and integrase in retrovirus

Question 52

env

Answer 52

encode envelope proteins in retrovirus