1) If a bacterium with a wildtype lac operon is grown in the presence of lactose
ID: 151798 • Letter: 1
Question
1) If a bacterium with a wildtype lac operon is grown in the presence of lactose, high levels of transcription result for a while, however, eventually transcription is again down-regulated. If, on the other hand, the sugar IPTG is present (instead of lactose), transcription levels are high and remain high. What function do IPTG and lactose share? How are they differently affected by the operon product?
2) If a wildtype bacterium is grown in the presence of the sugar X-gal, transcription of the polycistronic m-RNA does not occur. What is X-gal unable to do? Without adding lactose (or genetically modifying the bacteria), how could you fix this problem (Hint: see question 1)?
Explanation / Answer
Answer Q1)
Brief Summary of the Lac-Operon Concept:
What is IPTG?
IPTG is a Lactose Analog that is used for Experimental purposes. It is not metabolized by E.Coli,thus it maintains a sustained rate of transcription by binding (and inactivating) Repressor proteins.
LACTOSE AND IPTG:
2. PRODUCTS:
[NOTE: All Lactose is instantaneously converted into AlloLactose by Beta-Galactosidase : So Allolactose has been studied extensively and has been used to answer this question]
ANSWER Q2.
X-Gal is a Carbon-containing compound(similar to Lactose) used as an indicator to detect the presence of Beta- Galactosidase during a reaction.
The transcription and subsequent protein synthesis requires binding of Lactose to the Operator region.
Beta-Galactosidase which converts Lactose into AlloLactose needs to be inhibited since Allolactose binds to the Repressor region of the Lac-Operon.
X-Gal changes its' color only in the presence of Beta-Galactosidase and the production of a repressor substrate (i.e., Allolactose) results in cessation of Transcription.(DNA ---> mRNA).
The addition of IPTG to the X-Gal sugar composite will enhance the replication process exponentially due to the reasons mentioned above.
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