A student transforms competent cells with 2 ng of a plasmid…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student transforms competent cells with ng of a plasmid. She spreads one tenth of the cells on a plate with the antibiotic, and counts colonies.
- How much DNA was on the plate, in ng?
- How many colonies grow for each ng of DNA on the plate?
- What is the efficiency of the cells, in colonies for each microgram?
Need a reminder? The key ideaShow
Read a size from a ladder with a straight line of size against distance. An uncut plasmid shows a supercoiled band (fastest), a linear band and a nicked band (slowest). The control plates are: no DNA, uncut vector, cut vector without ligase, and cut vector with ligase and no insert. Efficiency colonies (ng of DNA on the plate) for each microgram.
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. ng; one tenth plated; colonies.
Plan. Efficiency is the colonies divided by the DNA on the plate, in micrograms.
Step 1. (a) ng.
Step 2. (b) colonies for each ng.
Step 3. (c) colonies for each microgram.
Answer: ng; colonies for each ng; colonies for each microgram.
Check. If all the cells had been plated, the colonies would be ten times more, , and the DNA ten times more, ng. The ratio is the same.
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