Chapter 19 Flashcards Preview

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Flashcards in Chapter 19 Deck (23):
1

virus

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

2

viral genomes may consist of either
1.
2.

1. double or single stranded DNA
2. double or single stranded RNA

3

capsid

the protein shell that encloses the viral genome
-built from protein subunits called capsomeres
-can have various structures

4

viral envelopes

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

5

bacterophages

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

6

viruses can only replicate where?

within a host cell

7

host rane

a limited number of hosts that it can infect

8

how does a virus dublicate

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

9

what are the two reproductive mechanisms of phages?

1. lytic cycle
2. lysogenic cycle

10

lytic cycle

culminates in the death of the host cell
-produces new phages and lyses (breaks open) the host's cell wall, releasing the progeny viruses

11

virulent phage

a phage that reproduces only by the lytic cycle

12

restriction enzymes

defense against phages
--recognize and cut up phage DNA

13

lysogenic cycle

replicates the phage genome without destroying the host
-everytime the host divides, it copies the phage DNA and passes the copies to daughter cells

14

prophage

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

15

temperate phages

use both lytic and lysogenic cycle

16

many viruses that infect animals have a ____ envelope

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

17

retroviruses

use reverse transcriptase to copy their RAN genome into DNA

18

what is an example of a retrovirus?

HIV that causes AIDS

19

provirus

the viral DNA that is integrated into the host genome

20

are vaccines helpful for viruses?

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

21

how can viruses spread disease in within plants

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

22

viroids

small circular RNA molecules that infect plants and disrupt their growth

23

prions

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