Chapter 6

Question 1

• Virion (virus particle)

Answer 1

has nucleic acid genome (DNA or RNA, single or double stranded) and capsid

Question 2

viriods

Answer 2

– RNA genome is itself the infectious particle

• Infect plants

Question 3

prions

Answer 3

– protein only (no nucleic acid)
• Abnormal protein structure
• Cause of “mad cow” disease

Question 4

Filamentous viruses

Answer 4

symmetrical virus with helical symmetry

•helical tube around genome

Question 5

tailed viruses

Answer 5

multipart structure
• Icosahedral capsid has genome attached to a helical “neck” that channels nucleic acid into host
• Example: T4 bacteriophage

Question 6

asymmetrical viruses

Answer 6

lack capsid symmetry

Question 7

Viruses may have

Answer 7

lipid envelope
• Allows fusion to host cell membrane
• Occurs if host cell is not covered by cell wall

Question 8

International Committee on Taxonomy of Viruses (ICTV)

Answer 8

• Genome composition –the Baltimore method
• Capsid symmetry (helical, icosahedral)
• Envelope
• Size

Question 9

How do we compare virus

genomes? No rRNA

Answer 9

based on orthologs–genes of common ancestry in two genomes that share same function

Question 10

Proteomic classification is useful for

Answer 10

viruses b/c their small genomes encode few proteins

Question 11

all viruses require

Answer 11

• Host recognition and attachment
• Genome entry
• Replicate genome
• Make viral proteins
• Assemble capsids
• Exit

Question 12

Cell-surface receptors

Answer 12

proteins on host that are specific to host species and bind to a specific component

Question 13

Lytic cycle

Answer 13

virus injects its genome into cell and reproduces as many virus’ as possible

Question 14

Lytic cycle phage genes
Early genes-
late gene-

Answer 14

• to produce new phage capsids etc

- after capsids are assembled; kills host and releasing new virus’

Question 15

burst-

burst size-

Answer 15

• lysis is also referred to as burst.

- number of particles released

Question 16

transduction

Answer 16

During exit from lysogeny the virus can get host genes, passes on to another cell

Question 17

Bacteriophage Life Cycle

Answer 17

Slow-release cycle
• Phage particles reproduce without killing host cell
• Phage M13

Question 18

bacterial host defenses

Answer 18

• Altered host receptor proteins (phage can’t bind)
• Restriction endonucleases
• CRISPR

Question 19

CRISPR

Answer 19

copies piece of phage and remembers it. for next infection, it recognizes and cleaves it.

Question 20

tropism

Answer 20

infect specific tissue type within a host

Question 21

broad tropism

Answer 21

infect many kinds of host tissues

Question 22

rna to rna

Answer 22

RNA-dependent RNA polymerase

Question 23

(+) ssRNA viruses

Answer 23

RNA-dependent RNA polymerase, generates - rna strand.

Question 24

(-) ssRNA viruses

Answer 24

used a template to create mRNA and progeny genomes

Question 25

in the beginning of eclipse period (when it drops)

Answer 25

viruses binds to host

Question 26

Eclipse period/Latent period

Answer 26

Replicating genomes and assembly, usually undetectable.

Question 27

Rise period

Answer 27

• Cells begin to lyse and progeny viruses are released

* Burst of phage