The occurrence of a particular restriction enzyme cleavage site in a DNA molecul

Question

The occurrence of a particular restriction enzyme cleavage site in a DNA molecule is simply a matter of chance. The enzyme Bgl II requires the sequence AGATCT to cleave DNA whereas the enzyme Asc I requires the sequence GGCGCGCC.

When incubated with bacteriophage DNA, (about 50,000 base pairs), Bgl II produces 7 DNA fragments whereas Asc I produces 3 fragments. Similarly, Bgl II cleaves the human adenovirus genome (about 39,000 base pairs) in 11 places whereas Asc I cleaves in only 2 places. Explain why on average, Bgl II cleaves a given DNA molecule at more sites than does Asc I.

Explanation / Answer

The enzyme Bgl II cleaves at the sequence AGATCT whereas the enzyme Asc I cleave at the sequence GGCGCGCC. In a genome the DNA sequences that are rich in AT sequences than the GC sequences are unstable. Since, bacteriophage and human adenovirus both are viruses, their genomes are highly unstable and are rich in AT sequences than GC sequences and hence, Bgl II cleaves more sites in DNA than Asc I restriction enzyme.

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