An enzyme cuts at every one of its sites…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
An enzyme cuts at every one of its sites.
- A straight DNA has sites. How many fragments does it give?
- A circular plasmid has sites for the same enzyme. How many fragments does it give?
- A circular plasmid has sites for enzyme A and sites for enzyme B. None of the five sites is at the same place. How many fragments does the plasmid give when both enzymes are used together?
Need a reminder? The key ideaShow
A restriction endonuclease cuts both strands inside its palindromic recognition sequence. A site of bases turns up by chance about once in bases. A straight DNA with sites gives fragments. A circular DNA with sites gives fragments.
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. sites on a straight piece; on a circle; on a circle.
Plan. A straight piece with cuts gives fragments. A circle with cuts gives fragments.
Step 1. (a) fragments.
Step 2. (b) fragments.
Step 3. (c) Total cuts: . A circle with cuts gives fragments.
Answer: fragments; fragments; fragments.
Check. Draw a circle and mark one cut. It becomes a line, in one piece. A second cut makes two pieces. So the number of pieces equals the number of cuts.
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