ch. 5 - intro to viruses

Question 1

what is the vital role of viruses?

Answer 1

are obligate intracellular parasites
- cannot multiply unless they invade a specific host cell + instruct its genetic and metabolic machinery to make and release new viruses

Question 2

are viruses alive?

Answer 2

• they are described as active or inactive

Question 3

what is virus latin for?

Answer 3

• means poison in latin

Question 4

what are the three things that classify a virus?

Answer 4

1) is infectious
2) host cell takes care of all needs
3) have own genetic material - either DNA or RNA

Question 5

what are the parts needed for a virus to invade and control a host cell?

Answer 5

• spikes: target
• capsid: external coating
• genetic material (either DNA or RNA)

Question 6

what is the capsid?

Answer 6

• protein shell that surrounds the nucleic acid
  nucleocapsid - the capsid together with the nucleic acid

Question 7

what is a naked virus?

Answer 7

• consists only of a nucleocapsid

Question 8

what is the envelope?

Answer 8

• external covering of nucleocapsid - usually modified piece of host’s cell membrane
• during budding

Question 9

what are the spikes?

Answer 9

• found on naked or enveloped viruses
• project from nucleocapsid or envelope
• allow viruses to dock with host cells

Question 10

what is a virion?

Answer 10

• a fully formed virus able to establish an infection in a host cell

Question 11

what are the three capsid shapes?

Answer 11

• helical
• icosahedral - 20 faces/12 corners
• complex

Question 12

what are the DNA viral genomes?

Answer 12

• single-stranded DNA genomes
• double stranded DNA genomes

Question 13

what are the RNA viral genomes?

Answer 13

• single-stranded RNA genomes
• double-stranded RNA genomes
• positive strand RNA viruses - have mRNA genomes
• negative strand RNA viruses - have RNA strand complementary to mRNA

Question 14

what are retroviruses?

Answer 14

• RNA is replicated indirectly through a DNA using an reverse transcriptase enzyme
• enzyme - takes RNA to DNA

Question 15

steps to how a virus infects?

Answer 15

1) attachment - to host plasma membrane via spikes
2) penetration - uncoating is the separation of the capsid from the genome
3) synthesis - virus uses the host’s cellular machinery to make more of it own nucleic acid + protein
4) assembly - parts of the virus are put together in stepwise fashion
5) release - after new viruses are assembled, envelope proteins are incorporated into a cellular membrane —- virus then buds, taking membrane part with it as an envelope

Question 16

what is a host range?

Answer 16

• the limited range of cells that a virus can infect

ex.) – hep B - liver cells of humans
– poliovirus - intestinal + nerve cells of primates
– rabies - various cells of all mammals

Question 17

what is a tropism?

Answer 17

• specificities of viruses for certain tissues

Question 18

what is endocytosis?

Answer 18

• when the entire virus is engulfed by the cell + enclosed in a vacuole or vesicle

Question 19

what happens during uncoating?

Answer 19

• enzymes in the vacuole dissolve the envelope and capsid

Question 20

what is it called when viral replication is normal?

Answer 20

lytic

Question 21

what is it called when viral replication when the virus stays in the host cell and replicates itself as the host cell replicates?

Answer 21

lysogenic - is hiding within host’s DNA

ex.) bacteriophage - infects and replicates only within bacteria

Question 22

what does CPEs mean?

Answer 22

cytopathic effects - virus-induced damage to the cell that alters its microscopic experience

ex.) - gross changes in shape + size
- development of intracellular changes
- inclusion bodies
- syncytia

Question 23

what are inclusion bodies?

Answer 23

• compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm

Question 24

what is syncytia?

Answer 24

• fusion of multiple host cells into single large cells containing multiple nuclei

ex.) respiratory syncytia virus (RSV)

Question 25

what are oncogenic viruses?

Answer 25

- experts estimate that up to 20% of human cancers are caused by viruses

Question 26

what does transformation mean?

Answer 26

effect on the cell caused by oncogenic viruses - increased rate of growth - alterations in chromosomes - changes in cell's surface molecules - capacity to divide for an indefinite period

Question 27

what are oncoviruses?

Answer 27

- viruses capable of initiating tumors

Question 28

what are the two ways a virus can use living cells as their medium?

Answer 28

- in vivo - laboratory-bred animals + embryonic bird tissues - in vitro - cell or tissue culture methods

Question 29

what are the primary purposes of viral cultivation?

Answer 29

- isolate + identify viruses in clinical specimens - prepare viruses for vaccines - do detailed research on viral culture, multiplication cycles, genetics + effects on host cells

Question 30

what are two ways that viruses can cause cancer?

Answer 30

1) put themselves into a control gene - protooncogenic gene 2) take a control gene w/ it

Question 31

what is a plaque?

Answer 31

- areas where virus-infected cells have been destroyed + show up as a clear, well-defined patches in the cell sheet ex.) microscopic manifestation of cytopathic effects - CPEs

Question 32

treatment of viral infections?

Answer 32

- antibiotics designed to disrupt prokaryotic cells have no effect on viruses - vaccines stimulate immunity

Question 33

what is an interferon?

Answer 33

- occurs naturally in human cells - used with some success in treating and preventing viral infections

Question 34

what are viroids?

Answer 34

- infectious RNA particles that can cause disease in crop plants - the replication cycle + disease causation process of viroids are not understood

Question 35

what are prions?

Answer 35

- infectious proteins - bad version of prions can cause transmissible spongiform encephalopathies --- in animals + humans mad cow disease = cow

Question 36

what can transmissible spongiform encephalopathies (TSEs) cause?

Answer 36

- death of host from nerve cell death leading to sponge-like holes in brain tissue symptoms: dementia, weakened muscles, loss of balance human form called Creutzfeldt-Jakob disease (CJD)

Question 37

what are protooncogenes?

Answer 37

- cells before cancer