Chapter 19

Question 1

Virus example

Answer 1

bacteriophage

Question 2

Bacteriophage

Answer 2

can infect and set in motion a genetic takeover of bacteria

-i.e. Escherichia coli (E. coli)

Question 3

Model systems

Answer 3

E. coli and its viruses because of their freuqnct use by researchers in studies that reveal broad biological principles

Question 4

Microbes

Answer 4

• have unique genetic mechanisms that are novel and interesting
• viruses and bacteria are this

Question 5

Molecular Biology

Answer 5

rooted in the study of viruses and their infection and takeover of cells
- i.e. bacteria

Question 6

Viruses

Answer 6

NOT living
NOT cells

ARE infectious particles made up of nucleotide and protein

• obligate intracellular parasites
• have a genome, but can reproduce one within a host cell (they’re parasites)
• small infectious particles consisting of nucleic acid enclosed in a capsid coat (proteins)

Question 7

Tobacco Mosaic Disease

Answer 7

stunts the growth of tobacco plants and gives their leaves a mosaic coloration
- RNA based virus

Question 8

Wendell Stanley

Answer 8

1935
confirmed that there is a particle smaller than bacteria that caused tobacco mosaic disease

• crystallized the infectious particle, TMV (tobacco mosaic virus)

Question 9

Viral genomes

Answer 9

may consist of either double- or single stranded DNA or RNA

Question 10

Capsid

Answer 10

composed of identical protein subunits and is the protein shell that encloses the viral genome
- come in various shapes and sizes (i.e. icsohedral)

Question 11

DNA-based virus example

Answer 11

herpes

Question 12

RNA-based virus example

Answer 12

HIV

Question 13

Some viruses may also consist of

Answer 13

nucleic acid enclosed in a membranous envelope from the host cell

• i.e. HIV, influenza virus
• membrane bound viruses are easy to inactivate by removing the membrane

Question 14

Bacteriophages (T4)

Answer 14

• also called phages

- have the most complex capsids found among viruses

Question 15

Viruses are

Answer 15

obligate intracellular parasites
meaning they can reproduce only within a host cell
- each virus has a limited number (range) or host cells it can infect

Question 16

Viruses use

Answer 16

the host cell enzymes, ribosomes, and molecules to synthesize progeny viruses

Question 17

Nature of the genome

Answer 17

the basis for the common classification of animal viruses

DNA vs. RNA

Question 18

Phages

Answer 18

the best understood of all viruses and go through 2 alternative reproductive mechanisms (lytic and lysogenic cycles)

Question 19

2 alternative reproductive mechanisms that phages go through

Answer 19

1) lytic cycle

2) lysogenic cycle

Question 20

Lytic Cycle

Answer 20

culminates in the death of the host and produces new phages and digests the host’s cell wall, releasing the progeny viruses

• TMV
• Rhinovirus
• Enterovirus (self-limiting)

Question 21

Lysogenic Cycle

Answer 21

replicates the phage genome without destroying the host

• Phage
• HIV
• VZV

Question 22

Temperate Phages

Answer 22

capable of using both the lytic and lysogenic cycles of reproduction

• phage lambda

Question 23

Latent Viruses

Answer 23

• Herpes (DNA based), integrated into genome (measles is a herpes-based virus)
• Varicella Zoster Virus
• HIV (RNA based)
• don’t kill the host cell (hanging around)
• produces new progeny

Question 24

Varicella Zoster Virus (VZV)

Answer 24

chicken pox => shingles
attach to spinal ganglia 
integrated into genome
will be reintegrated
lysogenic

Question 25

All viruses have

Answer 25

1) genome 2) capsid 3) membranous envelope (not all have)

Question 26

T4 lytic cycle

Answer 26

1) Attachment (to host cell surface) The T4 phage uses its tail fibers to bind to specific receptor sites on the outer surface of an E. coli cell - hast to have the right protein/capsid 2) Entry of phage DNA and degradation of host DNA The sheath of the tail contracts, injecting the phage DNA into the cell and leaving the empty capsid outside. The cell's DNA is hydrolyzed 3) Synthesis of viral genome and proteins The phage DNA directs production of phage proteins and copies of the phage genome by host enzymes, using components within the cell 4) Assembly Three separate sets of proteins self-assemble to form phage heads, tails, and tail fibers. The phage genome is packaged inside the capsid as the head forms 5) Release The phage directs production of an enzyme that damages the bacterial cell wall, allowing fluid to enter. The cell swells and finally bursts, releasing 100 to 200 phage particles

Question 27

Viruses' membrane envelopes

Answer 27

many have glycoproteins on their surface that bind to specific receptor molecules on the surface of a host cell

Question 28

Animal viruses utilize host cell machinery to make

Answer 28

new viruses

Question 29

Some viral envelopes are formed from the host cell's

Answer 29

plasma membrane as the viral capsids exit

Question 30

The broadest variety of RNA genome is found among the viruses that

Answer 30

infect animals

Question 31

Retroviruses

Answer 31

use reverse transcriptase to copy their RNA genome into DNA

Question 32

HIV (human immunodeficiency virus

Answer 32

- a retrovirus that causes AIDS (acquired immunodeficiency syndrome) - attacks and destroys immune cells called white blood cells - can convert its RNA genome into DNA, which can then be integrated into the host genome as a PROVIRUS

Question 33

Provirus

Answer 33

when an animal virus integrates its genome into the host cell DNA

Question 34

Diseases caused by viral infections affect ...

Answer 34

- humans (i.e. SARS and Herpes) - agricultural crops - livestock worldwide (>2000 types of plant viruses)

Question 35

Viruses may damage or kill cells by

Answer 35

causing the release of hydrolytic enzymes from lysosomes or they may cause infected cells to produce toxins that lead to disease symptoms

Question 36

Vaccines

Answer 36

derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen and can prevent certain viral illnesses

Question 37

What kinds of problems do viruses create for animal cells?

Answer 37

- a number of cytopathic or damaging effects 1) Changes in size and shape 2) Cytoplasmic and nuclear inclusion bodies (protein aggregates): "clumping" precipitates or clots 3) Cell fusion to form multinucleate cells 4) Inappropriate cell lysis (destruction) 5) Transform cells into cancerous (oncogenic) cells by altering DNA

Question 38

Normal cells are converted to cancer cells by the accumulation

Answer 38

multiple mutations affecting porto-oncogenes and tumor-suppressor genes

Question 39

Certain viruses promote cancer by

Answer 39

integration of viral DNA into a cell' s genome -i.e. herpes individuals who get infected with certain viruses may be at an increased risk of developing certain types of cancer -i.e. cervical cancer (papilloma virus)

Question 40

Some infectious agents behave like viruses but

Answer 40

do not infect cells although they cause disease

Question 41

Prions

Answer 41

misfiled proteins, contain no nucleic acid and cause spongiform encephalopathies or holes in the brain - cause scope in sheep and goats, boven spongiform encephalopahties (BSE) (aka mad cow disease) and Creutzfeldt-Jakob Disease

Question 42

Viroids

Answer 42

short pieces of RNA, no protein coat and have only been identifies in plants

Question 43

Enterovirus

Answer 43

small RNA viruses that belong to the group that includes the poliovirus coxsackieviruses, echoviruses, and other enteroviruses

Question 44

Non-polio-enteroviruses

Answer 44

the 2nd most common to the "common cold" viruses and cause an estimated 10-15 million or more symptomatic infectious a year in USA

Question 45

Enteroviruses can be found

Answer 45

in the respiratory secretions (saliva, sputum, nasal mucus) and stool of infected person

Question 46

Persons may be come infected by

Answer 46

direct contact with secretions or contaminated surfaces or objects, such as a drinking glass, door knobs, telephone

Question 47

In USA, infections caused by enteroviruses are most likely to occur during

Answer 47

the summer or fall

Question 48

Symptoms of enteroviruses include

Answer 48

mild upper respiratory symptoms, a flu-like illness with fever and muscle aches less commonly, some persons have "aseptic" or viral meningitis. Few infections result in myocarditis or death