Four steps of the isolation of DNA from bacteria are listed in a mixed order…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Four steps of the isolation of DNA from bacteria are listed in a mixed order.
A. Add chilled ethanol.
B. Add protease.
C. Treat the cells with lysozyme.
D. Add ribonuclease.
- Write the order in which the steps should be done.
- Which two steps can be done in either order, and why?
Need a reminder? The key ideaShow
The enzyme that opens a cell depends on its wall: lysozyme for bacteria, cellulase for plants, chitinase for fungi. Ribonuclease removes RNA, protease removes proteins, and chilled ethanol makes DNA appear. In a gel, DNA moves to the anode, and smaller fragments move farther. In the model of the lesson, distance .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Four steps, A to D.
Plan. Open the cell, remove the other molecules, and then bring out the DNA.
Step 1. The wall must be broken first, so C comes first.
Step 2. Ribonuclease (D) and protease (B) remove the RNA and the proteins. They can be done in either order, because each one acts on a different molecule.
Step 3. The ethanol (A) comes last. It makes the clean DNA come out of the solution as threads.
Answer: (a) C, then D and B, then A (C, D, B, A or C, B, D, A). (b) D and B, because they remove different molecules and do not depend on each other.
Check. If the ethanol were added earlier, the RNA and the proteins would come out with the DNA.
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