Results

You conduct your research on the same bacterial species as the doctor: E. coli. The following facts are known about this bacteria:

To test the Unidirectional Hypothesis, you decide to examine the replication process in action and see if it looks like the replication fork is travelling in one direction around the chromosome. You decide to do this by taking audioradiographs of the chromosome. Figure 1 is one of the audioradiographs that you took.

FIGURE 1: Replication of the E. coli chromomsome.

To test the Single-Fork Hypothesis, you decide to measure how long the E. coli chromosome takes replicate and compare this to how long it takes the population to double. You took the following readings from E. coli grown at 37 C on a glucose-rich medium:

Specimen Time(Seconds) Number of Nucleotides Replicated
A 10 10250
B 10 10030
C 10 9960
D 10 9700
E 10 10100
  Average=50040/5=10008 nucleotides

On average, as the table shows, E. coli replicates 10008 nucleotides per 10 seconds or about 1000 nucleotides per second.

After examining this data, you started to think that there was something wrong with Dr. Gen E. Tics Unidirectional and Single-Fork Hypotheses. What do you think is wrong? What parts of this data conflict with his claims? (Click on Discuss in the left margin after you come up with some ideas.)