In a restriction digest, the R- tube serves as which type of control?

In a restriction digest, the R- tube serves as which type of control?

• A. Negative control with no enzyme
• B. Positive control with enzyme
• C. Buffer control
• D. Temperature control

Answer: (B)

The key idea is using a control that confirms the enzyme is active and the digest can occur. The R- tube is set up with both the restriction enzyme and the target DNA, so it should show digestion when run on a gel. That makes it a positive control: it proves the system works and the enzyme is functioning as expected. Other controls serve different checks: a tube without enzyme shows what uncut DNA looks like (ensuring any observed cuts are enzyme-dependent), a buffer-only tube checks that the buffer itself doesn’t cause changes, and a temperature control verifies that incubation conditions are correct for digestion.

The key idea is using a control that confirms the enzyme is active and the digest can occur. The R- tube is set up with both the restriction enzyme and the target DNA, so it should show digestion when run on a gel. That makes it a positive control: it proves the system works and the enzyme is functioning as expected.

Other controls serve different checks: a tube without enzyme shows what uncut DNA looks like (ensuring any observed cuts are enzyme-dependent), a buffer-only tube checks that the buffer itself doesn’t cause changes, and a temperature control verifies that incubation conditions are correct for digestion.