1. There are two types of transduction: generalized and specialized.

Generalized Transduction (Figure 8.16)

1. Generalized transduction involves the transfer of any piece of the bacterial chromosome from one cell to another cell of the same species.

2. Generalized transduction can be carried out by virulent and temperate phages.

Specialized Transduction (Figure 13.11)

1. Specialized transduction involves the transfer of specific genes which is carried out only by temperate phages. Lambda is a well-studied specialized transducing phage.

2. Only genes located near the site at which the temperate phage integrates its DNA are transduced. Bacterial genes may attach to the phage DNA when the phage DNA excises from the bacterial chromosome.

3. Phage genes together with bacterial DNA replicate and code for the phage coat protein. The coat surrounds the bacterial and phage DNA, and, following lysis, the bacterial DNA is transferred to other bacteria in the environment.

13.4 Host Range of Phages

1. Several factors determine the host range of phage. These include the requirement that phage attachment proteins must bind to specific receptors on the bacteria, and the phage must circumvent the restriction-modification system found in all prokaryotes that degrades foreign DNA.

Receptors on the Bacterial Surface (Figure 13.12)

1. Most receptors are found primarily on the bacterial cell wall, but some phage attach to pili and flagella.

Restriction-Modification System (Figure 13.13)

1. All prokaryotes have restriction enzymes that recognize short sequences of bases in DNA and cleave, and thereby degrade the DNA at those sites. All prokaryotes have

Review Questions modification enzymes that add methyl groups to the bases modification enzyme. If the modification enzyme can in the short sequence so that they are not recognized by the methylate the sequences before the restriction endonuclease endonuclease and are not cleaved. Cells use this mechanism recognizes and cleaves the DNA, then the DNA will be to protect their own DNA from degradation. spared from degradation and will replicate. Its pattern of

2. When DNA from one strain of E. colt enters another strain, a methylation mU be identical to the DNA of the œU in which race is on between the restriction enzyme and the it is replicating, but different from the cell that it came from.

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