CPA #14 Questions

Question 1

why are viruses acellular?

Answer 1

noncellular; no cytoplasmic membrane; no cytosol or functional organelles

Question 2

why are viruses not considered living?

Answer 2

cannot carry out metabolic pathways; cannot grow; cannot respond to environment; cannot reproduce independently

Question 3

define: envelope

Answer 3

phospholipid membrane surrounding nucleocapsid

Question 4

define: capsid

Answer 4

protein coat surrounding a nucleic acid core

Question 5

define: virion

Answer 5

extracellular state of virus; made of capsid and envelope; (capsid/envelope help to protect and provide recognition sites that bind to complementary chemicals on host cells)

Question 6

explain the experiment to prove viruses are acellular

Answer 6

1892; russian microbiologist Dmitri Ivanowski; cause of tobacco mosaic disease; filtered sap of infected tobacco plants through porcelain filter small enough for the smallest of cells; virus passed through with the liquid, still infecting plants, proving that viruses lacked cells

Question 7

what are the five steps of lytic replication

Answer 7

1. attachment
2. entry
3. synthesis
4. assembly
5. release

Question 8

define: attachment

Answer 8

virion attaches to host cell

Question 9

define: entry

Answer 9

virion or genome enters host cell

Question 10

define: synthesis

Answer 10

nucleic acids and proteins are synthesized by host cells enzymes and ribosomes

Question 11

define: assembly

Answer 11

new virions are assembled in host cell

Question 12

define: release

Answer 12

new virions are released from host cell; killing host cell

Question 13

how is lysogenic replication different than lytic?

Answer 13

bacteriophages in lysogenic replication where infected host cells grow and reproduce normally for multiple generations before they lyse; aka lysogeny; phages = temperate phages or lysogenic phages

Question 14

define: induction

Answer 14

the trigger for the lytic cycle to start

Question 15

what are the 3 mechanisms of animal viral entry?

Answer 15

1. direct penetration
2. membrane fusion
3. endocytosis

Question 16

define: direct penetration

Answer 16

poliovirus; capsid attaches and creates porin cytoplasmic membrane; genome alone enters and capsid stays on surface

Question 17

define: membrane fusion

Answer 17

measles; viral envelope and host cytoplasmic membrane fuse; release capsid into cells cytoplasm; envelope glycoproteins stay on cell membrane

Question 18

define: endocytosis

Answer 18

adenovirus (naked) & herpesvirus (enveloped); attachment of the virus to receptor molecules on cell surface stimulates the cell to endocytize the virus

Question 19

what is the genetic material in retroviruses?

Answer 19

dsDNA from ssRNA

Question 20

how do retroviruses replicate?

Answer 20

reverse transcriptase transcribes dsDNA from the ssRNA genome which then serves as a template for the synthesis of additional ssRNA molecules which act as both mRNA and as a genome; HIV

Question 21

define: budding

Answer 21

process of how enveloped animal viruses are released; virions are extruded through one of the cells membranes

Question 22

define: persistant infection

Answer 22

host cells shed a virus slowly and steadily to allow infected cell to stay alive longer

Question 23

define: latency

Answer 23

virus remains dormant; latent or proviruses; can be prolonged for years without activity, signs, or symptoms

Question 24

what percent of cancers do viruses contribute to?

Answer 24

20-25%; viruses may carry copies of some oncogenes as part of genome; viruses may insert near to and promote oncogenes that are already present; viruses may interfere with normal tumor repression

Question 25

what are the three types of ways that viruses can be cultured?

Answer 25

1. media consisting of mature organisms
2. embryonated eggs
3. cell cultures

Question 26

why cant viruses be cultured in a test tube?

Answer 26

viruses cannot metabolize or replicate by themselves

Question 27

define: plaques

Answer 27

areas of a bacterial culture where the phages have lysed the bacteria; appear clear

Question 28

define: plaque assay

Answer 28

plaque corresponds to a single bacteriophage spreading and multiplying through the original bacterium-virus mixture

Question 29

why is culturing viruses in animals difficult?

Answer 29

maintaining lab animals can be difficult and expensive; raises ethical complications

Question 30

why are chicken eggs used to culture embryos?

Answer 30

inexpensive; among the largest of cells; free of contaminated microbes; contain a nourishing yolk which makes them self sufficient

Question 31

define: viroid

Answer 31

extremely small circular pieces of ssRNA that are infectious and pathogenic in plants

Question 32

define: prion

Answer 32

proteinaceous infective particles; lacks instructional nucleic acid

Question 33

describe how contaminated meat can be treated and safe to eat?

Answer 33

heating to 482C for 4 hours or autoclaving at 132C in concentrated sodium hydroxide for 1 hour; treatment with a 10% solution of phenolic compounds for 1 hour

Question 34

how are prion associated diseases treated?

Answer 34

no standard treatment; some drugs hold promise

Question 35

define: HeLa cells

Answer 35

derived from Henrietta Lacks who died from cervical cancer in 1951; continuous cell culture that allows for studies on cell metabolism, aging, and viral infection; unethical because of the money that was made off of these cells without her knowing they even took them

Question 36

how do prions replicate

Answer 36

PrP protein that misfolds, causes other PrP proteins to misfold, creating a sticky structure and cause holes

Question 37

define: naked virion

Answer 37

Extracellular state of virus; no envelope