Chapter 21

Question 1

viruses were first discovered by

Answer 1

Ivanowski

Question 2

are viruses cellular or acellular

Answer 2

acellular

Question 3

viruses have no metabolism and cannot grow

true or false

Answer 3

true

Question 4

obligate intracellular parasites and cannot replicate unless they are in the host cell using that cell’s machinery

Answer 4

viruses

Question 5

four virus shapes

Answer 5

helical, complex, enveloped and icosahedral

Question 6

each virion has

Answer 6

nucleic acid, a nucleocapsid, envelopes which are taken from the host cell

Question 7

is virus nucleic acid RNA or DNA?

Answer 7

EITHER

Question 8

are virus genomes single or double-stranded?

Circular or linear?

Answer 8

either!

Question 9

how does DNA help the virus to make copies of itself?

Answer 9

DNA tells the host to make new viruses, using the host equipment

Question 10

how do RNA viruses replicate

Answer 10

RNA may be directly transcribed or replicated first

RNA viruses may directly work like mRNA

Question 11

replication: uses host DNA polymerase
transcription: host RNA polymerase

Translation: host ribosomes

Answer 11

DNA viruses

Question 12

replication: enzyme called replicase makes new viral genome
transcription: it already looks like mRNA, needs to make mRNA

Host ribosomes are used to make proteins

Answer 12

RNA viruses

Question 13

how do we classify viruses?

Answer 13

Baltimore classification

Question 14

What are the steps of viral infections

Answer 14

attachment, entry, and replication/assembly

Question 15

receptors on the surface of the host cell bind to virus capsid proteins or virus envelope glycoproteins, viruses can attach only to cells that have the right receptor molecules

Answer 15

attachment

Question 16

bacteriophage DNA enters the cell “naked” (no envelope)

viruses may enter eukaryotic cells by endocytosis

Answer 16

entry

Question 17

DNA: transcribe mRNA –> make viral proteins, duplicate DNA to make new viral genomes

RNA: make complementary RNA if necessary to transcribe mRNA –> make viral proteins copy RNA to make new viral genomes

Answer 17

replication/assembly

Question 18

may involve lysis and death of the host cell, may involve budding, which does not directly kill the host cell

Answer 18

egress (release)

Question 19

breaking open host cell

Answer 19

lysis

Question 20

“steals the host membrane on the way out”, will eventually kill host but may take a long time

Answer 20

budding

Question 21

this type of virus is more likely to do endocytosis or inject genome, leaving the capsid outside

Answer 21

entry for naked viruses

Question 22

fuse with host membrane after attaching

Answer 22

enveloped viruses

Question 23

this type of virus usually lysis’ the enveloped virus bud out

Answer 23

exit for naked viruses

Question 24

bacteriophages are

Answer 24

bacterial viruses

Question 25

2 types of life cycles for bacteriophages

Answer 25

lytic and lysogenic

Question 26

causes lysis. the phage injects a cell into the host, the phage DNA circulates, remaining separate from the host DNA, and the phage DNA replicates and phage proteins are made. New phage particles are assembled and the cell lyses, releasing the phage

virus gets in, replicates, and lysis of host cell

Answer 26

lytic stage of the bacteriophage life cycle

Question 27

the phage injects a cell and conditions good recombination, the phage DNA becomes incorporated into the host genome, the cell divides and prophage DNA is passed on to daughter cells. Under stressful conditions, the phage DNA is excised from the bacterial chromosome and enters the lytic cycle

Virus gets in, it crosses over into the host chromosome and gets copied with the host chromosome every time the cell divides

Answer 27

lysogenic phase of the bacteriophage life cycle

Question 28

if you can get in genes that control the cell cycle or are involved in DNA repair

Answer 28

viruses that cause cancer

Question 29

latency and intermittent symptoms: remains in nerve tissue for life, reactivation causes active replication and cell lysis

Answer 29

animal viruses

Question 30

the virus inserts into either 1) DNA repair genes, or 2) genes that make proteins that control the cell cycle

Answer 30

oncogenesis

Question 31

virus typically enters by way of damaged plant tissue, may come from pollen, another plant, or vectors such as insect bites

Answer 31

horizontal transmission: plant viruses

Question 32

carrier of the virus

Answer 32

vector

Question 33

virus is transmitted from the parent plant

Answer 33

vertical transmission

Question 34

trigger immune protection, prepared using either an attenuated “live” virus or dead virus

Answer 34

vaccines to prevent viral infections

Question 35

how infectious the virus is

Answer 35

R naught

Question 36

will antibiotics eliminate viruses?

Answer 36

no, they will only kill bacteria

Question 37

keeps the virus from attaching and entering the host cell

Answer 37

fusion inhibitors

Question 38

drugs that inhibit an enzyme which would normally cut a long viral protein into smaller functional proteins

Answer 38

protease inhibitor

Question 39

inhibits the integration of the virus into the host genome

Answer 39

integrase inhibitors

Question 40

proteinaceous infectious particles

misfolded proteins that cause fatal neurodegenerative diseases

Answer 40

prions

Question 41

small circles of RNA, only known to infect plants, can replicate within cells, do not manufacture any proteins and can cause crop failures

Answer 41

virions

Question 42

mRNA vaccine design

Answer 42

S'methyl guanine cap 
Promoter/starter for start of protein synthesis 
Sequence of protein 
Stop sequence 
Poly A tail