Chapter 6

Question 1

virus

Answer 1

• infectious agents too small to be seen under a light microscope and are not considered cells
• viruses need a living host to replicate and multiply– obligate intracellular parasites
• each species of virus infects a particular group of host species= host range
• infectious, acellular pathogens
• DNA or RNA genome that is surrounded by a protein coat and in some cases, a phospholipid membrane studded with viral glycoproteins
• lack genes for many products needed for successful reproduction, requiring exploitation of host-cell genomes to reproduce

Question 2

tissue tropism

Answer 2

range of tissue types that a virus can infect

Question 3

host range

Answer 3

each species of virus infects a particular group of host species

Question 4

transmission

Answer 4

direct contact, indirect contact, or via a vector

Question 5

zoonose

Answer 5

when a virus is transmitted from an animal host to a human host

Question 6

reverse zoonose

Answer 6

when a virus is transmitted from a human host to an animal host

Question 7

viral specificity

Answer 7

kind of cells which a virus can infect

Question 8

vector

Answer 8

animals that transmit virus

Question 9

virion

Answer 9

complete virus particle

Question 10

nucleic acid

Answer 10

DNA or RNA, single or double stranded, linear or circular

Question 11

capsids

Answer 11

protects and encloses the nucleic acid, is composed of capsomeres

Question 12

envelope

Answer 12

• bilayer membrane (extra layer outside capsid)
• acquired when they bud from the cell
• composed of lipids, proteins, and carbs

Question 13

spikes

Answer 13

• glycoproteins
• mediate attachment to the host

Question 14

nucleocapsid

Answer 14

viral genome and capsid

Question 15

naked virus

Answer 15

virus without envelopes

Question 16

viral components

Answer 16

• a virus does not possess a ribosome nor an ATP generating mechanism
• during entry of the virus into a new host cell, the envelope fuses with the host membrane, releasing the viral contents into cytoplasm of cell
• after replicating, newly formed virions become enveloped by host cell membrane as they bud out of the host cell

Question 17

virus shape

Answer 17

• determined by either the capsomeres or the envelope
• plyhedral virus: capsid made up of triangular faces
• the space between the envelope and capsid may contain other proteins called tegument which may help with viral replication

Question 18

helical virus

Answer 18

capsid is cylindrical/rod-shaped with genome fitting just inside length of capsid
- nucleic acid is helical-> capsid forms cylinder around of it

Question 19

tailed bacteriophage

Answer 19

• sheath connects head to tail fibers
• tail fibers help virus attach to receptors on host cell’s surface

Question 20

amorphus

Answer 20

flexible wall, core enclosed loosely by envelope
- don’t have defined shape

Question 21

viral classification

Answer 21

• originally viruses were classified depending on the type of host infected
• the Internationaal Committee on Taxonomy of Viruses viral nomenclature based on: viral genetics, chemistry, morphology, and mechanism of multiplication
• The Baltimore classification system is based on: genome type and mRNA generation

Question 22

family names

Answer 22

end in viridae

Question 23

genus name

Answer 23

end in virus

Question 24

viral species

Answer 24

a group of viruses sharing the same genetic information and ecological niche (host)
- common names are used for species
- subspecies are designated by a number

Question 25

Coronaviridae

Answer 25

enveloped(+) sense RNA with 1 segments - spherical and bacilliform - cause upper respiratory infections

Question 26

retroviruses

Answer 26

- have reverse transcriptase that synthesizes complementary ssDNA copy using +ssRNA genome as a template - both -ssRNA and +ssRNA viruses need it ssRNA->dsDNA->integrates into host chromosome

Question 27

persistent viral infections

Answer 27

when a virus not completely clear from the host

Question 28

latent infections

Answer 28

- may initially cause an acute infection before becoming dormant - once dormant, virus remains hidden or dormant inside the cell (latency)

Question 29

chronic infections

Answer 29

- recurrent or persistent symptoms - occurs if body can't eliminate virus

Question 30

viroids

Answer 30

infections RNA particle smaller than a virus - not clear how they cause disease

Question 31

how do viroids differ from viruses

Answer 31

1. consists of a circular, single stranded RNA that doubles back on itself to form base pairs interrupted by short unpaired loops 2. exist inside cells as particles of RNA without capsids or envelopes 3. do not require a helper virus 4. viroid RNA does not produce proteins 5. copied in host cell nucleus or chloroplasts 6. viroid particles are not apparent in infected tissues

Question 32

virusoids

Answer 32

- similar size and structure of viroids but are dependent on, and encapsidated in, a helper virus - helper virus undergoes typical viral replication independent of viroid

Question 33

prions

Answer 33

- proteinaceous infectious particle - normal proteins which become folded incorrectly, maybe as a result of a mutation - the misfolded prion form of the protein accumulates and forms harmful aggragates that ultimately kill the cell - in the brain, cell death leads to tissue deteriorization and dementia

Question 34

characteristics of prion disease

Answer 34

1. resistant to inactivation by heating to 90C 2. not sensitive to radiation treatment 3. not destroyed by enzymes that digest DNA or RNA 4. sensitive to protein denaturing agents-- phenol, urea 5. direct pairing to amino acids

Question 35

viruses associated with cancer

Answer 35

- EBV: Burkitt's lymphoma - HPV: cervical cancer - HBV: liver cancer - HHV 8: Karposi's sarcoma - HTLV 1: adult T cell leukemia/lymphoma

Question 36

oncogenic DNA viruses

Answer 36

- adenoviridae - herpesviridae - poxviridae - papovaviridae - hepadnaviridae

Question 37

oncogenic RNA viruses

Answer 37

- retroviridae - viral RNA is transcribed to DNA, which can integrate into host DNA - HTLV-1 - HTLV-2