Chapter 19

Question 1

virus

Answer 1

a very small infectious particle consisting of nucleic acid enclosed in a portein coat and, in some cases, a membranous envelope

Question 2

viral genomes may consist of either
1.
2.

Answer 2

1. double or single stranded DNA

2. double or single stranded RNA

Question 3

capsid

Answer 3

the protein shell that encloses the viral genome

• built from protein subunits called capsomeres
• can have various structures

Question 4

viral envelopes

Answer 4

surround the capsids of inlfuenza viruses and many other viruses found in animals

• contain a combination of viral and host cell molecules
• membranous envelopes that help them infect hosts

Question 5

bacterophages

Answer 5

viruses that infect bacteria

• most complex capsids found among viruses
• elongated capsid head that encloses DNA
• protein tail piece attaches the phase to the host and injects the phage DNA inside

Question 6

viruses can only replicate where?

Answer 6

within a host cell

Question 7

host rane

Answer 7

a limited number of hosts that it can infect

Question 8

how does a virus dublicate

Answer 8

a viral genome has to enter a cell, the cell begins to manufacture viral proteins

• virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP and other molecules
• spontaneously assemble into new viruses

Question 9

what are the two reproductive mechanisms of phages?

Answer 9

1. lytic cycle

2. lysogenic cycle

Question 10

lytic cycle

Answer 10

culminates in the death of the host cell

-produces new phages and lyses (breaks open) the host’s cell wall, releasing the progeny viruses

Question 11

virulent phage

Answer 11

a phage that reproduces only by the lytic cycle

Question 12

restriction enzymes

Answer 12

defense against phages

–recognize and cut up phage DNA

Question 13

lysogenic cycle

Answer 13

replicates the phage genome without destroying the host

-everytime the host divides, it copies the phage DNA and passes the copies to daughter cells

Question 14

prophage

Answer 14

the integrated viral DNA

-viral DNA molecule is incorporated into the host cell’s chromosome

Question 15

temperate phages

Answer 15

use both lytic and lysogenic cycle

Question 16

many viruses that infect animals have a ____ envelope

Answer 16

membranous

• *some viral envelopes are formed from the host cell’s plasma membrane as the viral capsids exit
• *other viral membranes form from the host’s nuclear envelope and are then replaced by an envelop made from the golgi apparatus membrane

Question 17

retroviruses

Answer 17

use reverse transcriptase to copy their RAN genome into DNA

Question 18

what is an example of a retrovirus?

Answer 18

HIV that causes AIDS

Question 19

provirus

Answer 19

the viral DNA that is integrated into the host genome

Question 20

are vaccines helpful for viruses?

Answer 20

yes, they stimulate the immune system to mount defenses against the harmful pathogen
-they can prevent viral illnesses

Question 21

how can viruses spread disease in within plants

Answer 21

1. horizontal transmission, entering through damaged cell walls
2. vertical transmission, inheriting the virus from a parent

Question 22

viroids

Answer 22

small circular RNA molecules that infect plants and disrupt their growth

Question 23

prions

Answer 23

slow-acitng, virtually indestructible infectious proteins that cause brain diseases in mammals
-convert normal proteins into the prion version