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Viruses
Page 7

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FIG 19-4.

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DNA into the host cell through the weak spot in the wall. The empty capsid remains on the outside of the cell. In contrast, many viruses enter their host cell intact. Once inside, the capsid dissolves and the genetic material is released. This process is called uncoating.

3. During replication the viral DNA takes complete control of cell activity. It inactivates the E. coli DNA. The genes contained in the DNA of the viral genome then take over. They direct the cell to make viral DNA and the viral proteins that make up the structural portions of the phage. This happens when viral DNA makes RNA from nucleotides in the host cell by using the enzymes of the host cell.

4. During assembly proteins coded for by phage DNA act as enzymes that put new virus particles together. The entire metabolic activity of the cell is thus directed toward assembling new T4 phages. The result is a cell stuffed with new viruses.

S. During release the T4 phages release an enzyme that digests the bacterial cell wall from within. The disintegration of the infected host cell, called lysis (LIE-siss), allows new viruses to leave the cell. The new virus particles can then infect other cells, and the process can start again.

The Lysogenic Cycle

During the lytic cycle viruses enter the cell, use its components to make new viruses, and destroy the cell in one continuous process, which usually takes a day or two. However, some temperate viruses can infect a cell without causing its immediate destruction. Temperate viruses undergo a kind of life cycle called a lysogenic cycle, which has been most thoroughly studied in bacteriophages. Study this cycle in Figure 19-6 on the following page as you read.

 

FIG 19-5.

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Copyright 1995 Mr. Lewis Classroom for Physics & Biology. All rights reserved.