Shown below (Fig. 2 panels A and B) are batch culture growth curves for S. pneum

Question

Shown below (Fig. 2 panels A and B) are batch culture growth curves for S. pneumoniae growing in minimal media containing either glucose (A) or lactose (B) as energy source. Also shown on these curves are the levels of glucose or lactose remaining in the media as growth of the culture proceeds.

Shown below (Fig. 3) is a batch culture growth curve for S. pneumoniae growing in minimal broth containing BOTH glucose (2 millimolar) and lactose (2 millimolar) as energy sources (different phases of this diauxic growth curve are labeled a-e, and these will be referenced in the questions below).

Fig. 3: Growth curve for S. pneumoniae in media with both glucose and lactose.

6a. (3 pts). Draw a diagram depicting what CcpA, LacR, and RNA polymerase are doing at the lacFEG promoter during phase b of Figure 3.

6b. (1 pt). What carbon source is being utilized during phase b?

6c. (2 pts). In phase c, the growth curve levels off temporarily. Why? Why does it level off and why is                        this leveling off temporary?

Now, consider phase d of the growth curve:

6d. (3 pts). Draw a diagram depicting what CcpA, LacR, and RNA polymerase are doing at the lacFEG promoter during phase d of Figure 3.         

6e. (1 pt) What carbon source is being utilized during phase d?

-Log (# cells) '"… [Glucose] (millimolar) -Log (# cells) [Lactose] (millimolar) ) 107... ) 107 A| BI ]r ea ea so so - c li al Li Incubation Time 10 Incubation Time

Explanation / Answer

6a. Initially Glucose is utulize by cells and Lac operon is OFF.
LacR is expressed and transcription of the lac genes of lac promoter lacFEG repressed.                                CcpA complex blocked the transcription of RNA polymerase.

6b. Glucose

6C. It consume all the glucose in the medium now it has to adapt for new environment Lactose. So, it take some time for Lac operon thats why it is temporarily off.

6d. Lactose presence

lacR expression is repressed, and transcription of the lac operon is induced by lac promoter lacFEG .
CcpA complex not formed the transcription of RNA polymerase occurs.

6e. lactose

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