viruses

Question 1

are viruses alive?

Answer 1

• can’t reproduce without assistance
• lack machinery for energy harvesting, proteins synthesis, etc (must borrow this machinery from host cell)
• “obligate intracellular parasites” (must be in host)
• so no

Question 2

general virus characteristics

Answer 2

• non-cellular parasites
• they have either DNA or RNA never both
• goal of virus is not to kill host

Question 3

dormancy

Answer 3

some virus form crystalline structures and remain unchanged in an inactive state for years until they meet a receptive host (ex: tobacco mosaic office)

Question 4

capsid

Answer 4

where nucleic acids are stored. in some viruses it is covered in a protein envelope

Question 5

virus size

Answer 5

virus size varies, but they are very small. 20nm to 300nm

Question 6

bacteriophage

Answer 6

virus that attacks bacteria only

Question 7

parts of bacteriophage

Answer 7

-head (capsid and nucleic acid core)
-tail (contractile sheath, tail fiber, base plate with tail pins)
see ppt for chart

Question 8

virus diversity

Answer 8

many shapes and sizes, easily mutate

Question 9

viral reproduction

Answer 9

• highly efficient
• rapid evolution
• can give host new phenotypes
• RNA replication lacks proofreading mechanisms so mutating rate is higher

Question 10

viral replication cycle steps

Answer 10

• attachment (absorption)
• penetration (entry)
• replication
• assembly and maturation
• release

Question 11

attachment

Answer 11

• “absorption”
• virus binds to host cell
• viral surface proteins bind to cell surface receptors = high specificity

Question 12

entry

Answer 12

• “penetration”
• viral genetic material enters cell
• various mechanisms, portions of the virus may remain outside host cell

Question 13

lytic cycle

Answer 13

• in bacteria only
• when a dormant virus becomes infected
• most signals are unknown

Question 14

lysogenic cycle

Answer 14

• in bacteria only

- phage integrates nucleic acid into the host cell’s DNA creating a provirus that becomes dormant

Question 15

retrovirus

Answer 15

• RNA viruses
• after the virus enters a cell the RNA is turned to DNA via reverse transcriptase
• HIV

Question 16

transduction

Answer 16

viruses will introduce pieces of a hosts genetic material into that of another related or unrelated host. could influence evolution

Question 17

phenotypic mixing

Answer 17

• animal cells sometimes simultaneously infected by two viruses
• viral genetic material and viral capsids mismatched
• can facilitate interspecies gene transfer

Question 18

herpes virus

Answer 18

• 100 strains

- cold sores, chickenpox, shingles, mono, genital herpes

Question 19

HIV

Answer 19

• causes AIDS
• attacks T cells and reduces the function of immune system
• secondary function can be deadly
• descendants of bubonic plague survivors are immune

Question 20

HPV

Answer 20

• papilloma virus
• causes warts
• can cause cervical cancer
• about 50% of sexually active people contract it at some point

Question 21

epidemic

Answer 21

affects many people where disease wasn’t prevalent before

Question 22

pandemic

Answer 22

an entire country, continent or whole world

Question 23

endemic

Answer 23

found in an isolated place like the tropic flu

Question 24

epidemiology

Answer 24

studying the spread of the disease

Question 25

viroids

Answer 25

• infectious RNA molecules that cause disease in various plants
• their genome are much smaller than those of viruses (up to 400 nucleotides of circular single stranded RNA) and do not code for any proteins

Question 26

prions

Answer 26

• infectious agent made of protein
• able to fold in many ways
• makes them transmissible to other organisms
• often found in brain tissue
• examples: Creutzfeldt-Jakob disease, and mad cow disease