The bacteriophage lambda genome can exist in either a linear form (see Figures 15.1 and 15.8) or a circular form. How many fragments will be formed by restriction enzyme digestion with XhoI alone, with XbaI alone, and with both XhoI and XbaI in the linear and circular forms of the lambda genome?

Key Concepts

Bacteriophage Lambda Genome Structure

The bacteriophage lambda genome can exist in two forms: linear and circular. The linear form is typically found during the infection process, while the circular form can occur after the genome is integrated into the host's DNA. Understanding these forms is crucial for predicting how the genome will behave during restriction enzyme digestion.

Restriction Enzymes

Restriction enzymes, such as XhoI and XbaI, are proteins that cut DNA at specific sequences. XhoI recognizes the sequence CTCGAG, while XbaI recognizes the sequence TCTAGA. The number of fragments produced by digestion depends on the number of recognition sites present in the DNA, which varies between the linear and circular forms of the genome.

DNA Fragmentation and Analysis

When a DNA molecule is cut by restriction enzymes, it is fragmented into smaller pieces. The number of fragments generated can be calculated based on the number of cutting sites and the form of the DNA. In the case of the lambda genome, analyzing the resulting fragments from different enzyme combinations helps in understanding the genome's structure and the effects of the enzymes used.