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Name_____________________________
Date__________________________
12.2 Viruses – Student Handout
Fill in the missing blanks.
Bacteriophage Structure
What is a virus?
 A non-cellular particle made up of
___________________ that is surrounded by a
protective coat of ____________ called
____________
 Its genetic material can be either _________ or
_________
 It is closely related to prokaryotes because __________________________________________
_ but is not classified as a prokaryote
 A virus does not metabolize energy or undergo
________________________
 It is not classified into any ______________ because ____________________________
How do viruses survive?
 Viruses are parasites
o ________________________________________________________________________
_________________________________________________________________
 Invade _________________________________ and take over its cellular functions by altering
its _____________________________
 Bacteriophage is a virus that only infects bacteria, plant viruses only infect plants.
What are the two ways that a virus can reproduce?
1.
2.
LYTIC CYCLE: BACTERIOPHAGE INVADES E. coli
Step 1
Step 3
o bacteriophage attaches to cell wall
o Tails of virus specifically fit onto
bacterium’s cell wall.
o Virus releases enzyme that
dissolves bacterium cell wall
o Viral DNA is injected into cell
Step 2
o Host cell’s DNA is destroyed
o Viral DNA takes over host cell
and instructs cell to make copies of
virus DNA and capsid
o New viral DNA and capsid are
assembled into viruses
Step 4
o Virus produces lytic enzyme that
causes host cell to lyse (break down)
o Host cell is destroyed
o New viruses are released and can
infect other cells
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Step 6
Step 7
Step 1
Step 5
Step 2
Step 4
Step 3
Describe the lysogenic cycle:
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
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Are bacteria defenseless to viruses?
 Bacteria have enzymes called ___________________________.
 Restriction enzymes detect ______________ DNA, in this case viral DNA, and try to
______________________. How? Restriction enzymes are like scissors and
_______________________________

________________ and ________________ are in ______________________ with each other
for survival. Bacteria have effective restriction enzymes and viruses will try to develop
resistance to them.
Comparing Lytic and Lysogenic Cycle
Lytic Cycle
Lysogenic Cycle
Entry of virus
Fate of host cell after virus enters
How long does it take to release
new virus
Length of time before you see viral
symptoms
End result of cycle
What are RNA viruses?
 RNA viruses contain __________ as genetic material and not __________
 Viral RNA can do the following:
1. act as mRNA once it has entered the host cell. The mRNA can be used as a template for
translation to create __________________
OR
2. act as a template for transcription. In this case, viral RNA is transcribed to create
___________. The mRNA strand that is created can be used to translate viral protein
 Viral RNA provides its own instruction and does not interact with host’s ____________
 Therefore, RNA viruses undergo ____________ cycle because
________________________________________________________________________
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What is a retrovirus?
 Retroviruses contain ________ as genetic material and not __________
 When retroviruses enter the host cell, they “take over” by instructing the host to use viral
_______ code to create viral ______. Reverse transcriptase is an _____________ involved in
the synthesis of new viral DNA from viral RNA.
 Viral DNA becomes a permanent part of the host’s _______________ ________________. The
host’s new genetic makeup now consists of a combination of _________ DNA and the
____________ DNA. The “new” DNA can be used as a template to transcribe viral RNA and
thus, translate viral protein.
 Transcription is the process where DNA is used as a template to transcribe _________.
Retroviruses, however, initiate the reversed process of transcription where viral RNA is used as a
template to transcribe ____________. The reversed process of transcription is implied in the
virus’ name “retro” meaning backwards
 This cycle of viral infection is _____________ because
__________________________________
____________________________________________________________________________
 Examples of retrovirus: HIV, which causes AIDS