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Name: _____________________________
Period: ____________
Infective Cycles of Viruses
Textbook reference: L2 Biology section 16.5, L3 Biology section 19-3.
Viruses are particles that enter living cells and use the cell’s machinery to produce more virus particles. Some viruses destroy the
host cell immediately after they infect it. Others incorporate their genetic material into the host and may remain inactive for
several generations. Study the two different infective cycles of viruses illustrated below, then complete the following paragraph
using your text to assist.
A
C
D
B
The unshaded portion of the diagram shows a _______________________ cycle. It begins when a specific
type of virus called a (A) _____________________________ attaches to a (B) _______________________.
The tail of A releases an ______________________ that breaks down the cell surface of B. The outer
portion of the tail of A contracts and the (C) _____________________________________ is injected into B.
Inside the cell, C takes over. The cell B is directed to make copies of C and of the viral protein coat called a
_______________________. The protein coat and C are then assembled into ________________________
_____________________________. Before long the cell C bursts open in a process called ______________
and hundreds of new viral particles are released.
The shaded portion of the diagram represents a ____________________________ cycle. This cycle differs
from the previous cycle in that it includes the process by which (D) _______________________________
becomes part of the DNA of B. When B copies its own DNA during replication, the __________________
is also _______________________________. This process can be repeated for ______________________
______________________________. Eventually some factor will trigger a change in the cell and the D will
exit the host DNA and enter the _________________________ cycle, resulting in the release of new
_________________________________________________.