Two batches of phages were used to infect bacteria, as in the experiment of Hershey and Chase…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Two batches of phages were used to infect bacteria, as in the experiment of Hershey and Chase. After blending and spinning, the radioactivity of each tube was counted.
In the tube with the 35S phages, the liquid gave counts a minute and the pellet gave counts a minute. In the tube with the 32P phages, the liquid gave counts a minute and the pellet gave counts a minute.
- What per cent of the 35S label is in the liquid?
- What per cent of the 32P label is in the pellet?
- Which molecule of the phage entered the bacteria?
Need a reminder? The key ideaShow
The worked solution
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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. 35S tube: liquid , pellet . 32P tube: liquid , pellet (counts a minute).
Plan. Find each total, then the share in the part asked.
Step 1. Total of the 35S tube. counts a minute.
Step 2. (a) .
Step 3. Total of the 32P tube. counts a minute.
Step 4. (b) .
Step 5. (c) Most of the 32P is inside the bacteria, and most of the 35S is outside. So the DNA entered the cell.
Answer: ; ; DNA.
Check. The two shares of a tube add up to (for the 35S tube, ).
Watch out. Not all of the label is in the expected place, because the blending is never perfect. The result is the large share, not all of it.
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