Biol 2051- Exam 2: Ch. 6

Front 1

Properties of Viruses

Back 1

(1) intracellular parasite made of nucleic acid surrounded by protein coat
(2) only replicates inside host
(3) NO nucleus, organells, cytoplasm

Front 2

Capsid
(definition)

Back 2

protein coat surrounding nucleic acids

Front 3

Types of Capsids

Back 3

(1) Icosahedral (animal)
(2) Filamentous
(3) Complex (bacteriaphages)
(4) Asymmetrical (larger)

Front 4

Icosahedral capsids

Back 4

> Roughly spherical
> 20 equilateral faces

many animal viruses

Front 5

Filamentous capsids

Back 5

long tube of protein with genome inside
> tube made of hundreds of identical protein subunits
> tube length reflects size of viral genome

Front 6

Complex capsids

Back 6

>mixture of icosahedral and filamentous shapes

many bacteriophages

Front 7

Asymmetrical capsids

Back 7

tend to be larger viruses

poxviruses

Front 8

Virus Envelope

Back 8

lipid bilayer around capsid of some viruses

> allows fusion to host cell membrane
> envelope lipids come from host

Front 9

Things encoded in virus genome

Back 9

Viral proteins
(1) capsid
(2) proteins in envelope (if enveloped)
(3) any polymerase not in host cell

Front 10

Two types of cycles in bacteriophage

Back 10

(1) Lytic
(2) Lysogenic

Front 11

Lytic cycle

Back 11

phage quickly replicates and kills host cell
Ex: T4

Front 12

Lysogenic cycle

Back 12

integration of the bacteriophage nucleic acid into the host's genome
> at later point enter lytic cycle
Ex: Lambda

Front 13

lysogeny

Back 13

the viral genome integrates into host chromosome and is replicated with host chromosomes

Front 14

prophage

Back 14

when virus' genome exists as part of host genome

Front 15

lysogens

Back 15

bacterial host cells that harbor prophages

Front 16

Stages of Bacteriophage Life Cycle

Back 16

(1) attachment
(2) injection of genome
(3) replication of genome
(4) synthesize capsids
(5) assemble progeny
(6) exit from cell

Front 17

Types of Bacteriophage Exits from cell

Back 17

Lysis
> makes protein to depolymerize peptidoglycan
> host cell bursts

Slow release
> filamentous phages can extrude individual progeny through cell envelope

Front 18

Plaque assay

Back 18

Plaque: clearing of lysed bacteria in a lawn

count pfu (plaque forming units)

> used to count bacterial and some animal viruses

Front 19

Restriction endonucleases

Back 19

cleave DNA at specific sequences

> used to degrade foreign DNA

Front 20

Four Types of Infection
by animal viruses

Back 20

(1) Lytic
(2) Persistent
(3) Latent
(4) Transformation

Front 21

Lytic infection by animal virus

Back 21

destruction of host cell

Front 22

Persistent infection by animal virus

Back 22

new virions leave host by budding

cell does not die, but remains infected and produces virions indefinitely

Front 23

Latent infection by animal virus

Back 23

Virus not actively replicating, dormant

> symptoms appear when virus emerges from latency

Front 24

Transformation infection by animal virus

Back 24

virus can change normal cell into cancer cell

>benign or malignant tumors

Front 25

Types of RNA viruses

Back 25

(1) Positive-strand RNA virus (ss)
(2) Negative-strand RNA virus (ss)
(3) Double-stranded RNA virus

Front 26

Positive-strand RNA virus

Back 26

RNA genome is used directly as mRNA for making proteins

EX: poliovirus, rhinoviruses (cold viruses)

Front 27

Negative-strand RNA virus

Back 27

RNA genome does not serve directly as mRNA for making proteins;
transcribed into a complement that functions as mRNA

EX: rhabdoviruses (rabies), Ebola virus, measles, influenza

Front 28

Double-stranded RNA virus

Back 28

the enzymes required for endogenous transcription are part of the virion structure

EX: Reoviruses (only animal viruses with dsRNA)
> Rotavirus (stomach flu, diarrhea)

Front 29

DNA virus

(and examples)

Back 29

a virus that has DNA as its genetic material and replicates using a DNA-dependent DNA polymerase

ssDNA virus: parvoviruses
dsDNA virus: herpesvirus group, poxvirus group

Front 30

Herpesvirus group

Back 30

dsDNA virus; capable of latency for years, active during stressful conditions

EX: cold sores, veneral disease, chicken pox

Front 31

Poxvirus group

Back 31

dsDNA virus

EX: smallpox, cowpox, some tumors

Front 32

Retroviruses

Back 32

ssRNA genome

reverse transcriptase copies RNA into DNA
> DNA integrates into host genome (stage considered: provirus)
> DNA is transcribed into mRNA and RNA for new viruses

EX: HIV and some forms of cancer

Front 33

Viriods

Back 33

small, naked ssRNA
(no capsid, no envelope)

> mostly crop diseases
> believed to cause effects through RNA silencing

Front 34

Prions

Back 34

Protein-only infectious agent
> normal protein takes on abnormal shape, loses normal function, abnormal shape more stable

EX: BSE (mad cow), scrapie (sheep), Creutzfeld-Jakob, kuru (humans)

Front 35

Tenants of Viral Ecology

Back 35

(1) viruses present in all environments
(2) viruses limited by host population density
(3) Viruses increase host diversity (strong selection for virus-resistant strains)
(4) People susceptible if exposed to new virus