What observation indicates complete digestion in the R+ lane?

What observation indicates complete digestion in the R+ lane?

• A. Three bands are present.
• B. A single uncut plasmid band remains.
• C. Only two bands are present.
• D. No bands appear.

Answer: (C)

The key idea is that you can judge whether a restriction digest is complete by the pattern of bands you see on the gel. If every plasmid molecule is cut, you’ll only observe the fragments produced by that digestion and not the intact, uncut plasmid form. In this setup, complete digestion yields two fragments from the plasmid, so the gel should display two bands. That means all plasmid molecules were cut and there’s no remaining uncut supercoiled plasmid form. If any uncut plasmid remained, you’d expect an additional band corresponding to that intact form (or a different pattern), indicating incomplete digestion. So two bands on the R+ lane best indicate complete digestion.

The key idea is that you can judge whether a restriction digest is complete by the pattern of bands you see on the gel. If every plasmid molecule is cut, you’ll only observe the fragments produced by that digestion and not the intact, uncut plasmid form.

In this setup, complete digestion yields two fragments from the plasmid, so the gel should display two bands. That means all plasmid molecules were cut and there’s no remaining uncut supercoiled plasmid form. If any uncut plasmid remained, you’d expect an additional band corresponding to that intact form (or a different pattern), indicating incomplete digestion. So two bands on the R+ lane best indicate complete digestion.