Compound Purification Practice Test

To isolate DNA from a cell pellet, a student is performing an extraction using phenol and chloroform. The cells were lysed with 0.5mL of lysis buffer. 0.5mL extraction solution, consisting of phenol:chloroform:isoamyl alcohol (25:24:1), was added to the lysate. The sample was centrifuged at high speed for five minutes. The liquid in the tube was separated into three phases after centrifugation (see diagram).

In which layer will nucleic acids (RNA and DNA) be found?

To isolate DNA from a cell pellet, a student is performing an extraction using phenol and chloroform. The cells were lysed with 0.5mL of lysis buffer. 0.5mL extraction solution, consisting of phenol:chloroform:isoamyl alcohol (25:24:1), was added to the lysate. The sample was centrifuged at high speed for five minutes. The liquid in the tube was separated into three phases after centrifugation (see diagram).

The student saves the layer containing nucleic acids and transfers it to a new tube. The student then adds ethanol and salt, and centrifuges the solution at high speed. Where is the DNA in this new solution after centrifugation?