1. The figure to the right shows what happened in fl ask #9 in Dr. Lenski’s stud
ID: 204077 • Letter: 1
Question
1. The figure to the right shows what happened in fl ask
#9 in Dr. Lenski’s studies. Based on this fi gure:
a. What does OD mean and what does it represent?
b. What do higher OD values at generation ~33,000 tell
us about the population of E coli growing in flask #9?
c. What changes in cell function allowed this happen?
2. Acetyl Co-A is the normal input to citric acid cycle
reactions. What is the original molecule that E. coli
breaks down to produce Acetyl Co-A? How does it get into the cell?
3. What happens to citrate in E. coli when oxygen is not present?
4. What is the advantage to E. coli of being able to import citrate under conditions both with and without oxygen?
5. Application question: Why is succinate important when explaining that E. coli evolved to take up citrate under
conditions with oxygen?
0.30 0.25 0.20 8 0.15 0.10 0.05 0.00 30,000 31,000 32,000 33,000 34,000 35,000 GenerationExplanation / Answer
Ans. 1a OD means the absorbance or the optical density of the sample and it represents the growth rate of the organim over a period of time.
Ans. 1b Higher OD values at 33000 suggests that the long term adaptation to specific environment would elevate the population genetic process leading to an increased population.
Ans. 1c It may be molecular base of adaptation which enhanced the rate and reproducibility of the bacteria. Resistance to antibiotics is also another vital breakthrough for the organism to elicit such response.
Ans 2. The originating molecule for E.coli to produce acetyl CoA is pyruvate with the help of enzyme pyruvate dehydrogenase complex. It gets into the cell by oxidation of fatty acids and amino acids through oxygen in the medium.
Ans 3. In the abscence of oxygen glucose is metabolised to pyruvate throught the glycolysis which results in generation of 2 molecules of NADPH and 4 molecules of ATP.
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