A culture of a recombinant bacterium is followed for a day…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A culture of a recombinant bacterium is followed for a day. The number of cells in every millilitre was counted at six times.
- At h: .
- At h: .
- At h: .
- At h: .
- At h: .
- At h: .
- Which two counts are in the log phase?
- Which count is in the lag phase?
- What is the phase at h, and why does the number stay about the same?
Need a reminder? The key ideaShow
A batch culture has a lag phase, a log phase, a stationary phase and a decline phase. In the log phase the number doubles at a steady pace, . A recombinant protein comes from a gene that is expressed in a host of another species.
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. Six counts of a culture.
Plan. Compare the change from one count to the next. A fast, steady multiplication is the log phase. A small change at the start is the lag phase.
Step 1. From h to h, the number changes only a little, to . This is the lag phase.
Step 2. From h to h, and from h to h, the number is multiplied by a large factor. These counts, at h and at h, are in the log phase.
Step 3. From h to h, the number grows only from to , which is slower. The culture is slowing down, and by h the count is almost the same as at h. This is the stationary phase.
Answer: (a) h and h. (b) h (and the start). (c) The stationary phase, because food runs short and wastes build up, so new cells are made only as fast as old cells die.
Watch out. A level count can be the lag phase, at the start, or the stationary phase, at the end. The position in time tells you which.
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