Question

You have a circular plasmid containing 9 kb of DNA, and you wish to map its EcoRI and BamHI sites. When you digest the plasmid with EcoRI and run the DNA on a gel, you observe a single band at 9 kb. You get the same result when you digest the DNA with BamHI. When you digest with a mixture of both enzymes, you observe two bands, one 6 kb and the other 3 kb in size. Explain these results. Draw a map of the restriction sites.

Answer 1

Answer:

A nick is created between G and A in GAATTC when using Eco R1 site while a nick is generated between G and G in GGATCC when Bam H1 is used. The difference in the nicks created is the main reason you observe two bands when you digest the circular plasmid with a mixture of both

Explanation:

Circular plasmid containing : 9 kb of DNA

Eco R1 and Bam H1 are known as restriction sites in DNA ( i.e. special sequences found in a DNA ) hence they can  be specifically cleaved by the restriction enzymes enabling the insertion of a gene. that is why you will get a same result when you digest the Plasmid with either Eco R1 or Bam H1

but A nick is created between G and A in GAATTC when using Eco R1 site while a nick is generated between G and G in GGATCC when Bam H1 is used. The difference in the nicks created is the main reason you observe two bands when you digest the circular plasmid with a mixture of both