The lac operon has three paradoxes

if the operon is in a repressed state, how does the inducer enter the cell to start the process of induction

 If the operon is in a repressed state, how Repressor is removed with allolactose 

 How is allolactose synthesized in Repressed state Answer is Leaky Expression

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#Unit 3. Fundamental Processes

Mutations are also caused by compounds that substitute for normal bases (base analogs) or slip between the bases (intercalating agents) to cause errors in replication. 

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#Unit 3. Fundamental Processes

One of the most mutagenic base analogs is 5-bromouracil, an analog of thymine.

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#Unit 3. Fundamental Processes

The presence of the bromo substituent allows the base to mispair with guanine via the enol tautomer

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#Unit 3. Fundamental Processes

5-bromouracil induces transitions in both directions, A:T ↔ G:C.

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#Unit 3. Fundamental Processes

Tautomeric forms of the four common bases in DNA.

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#Unit 3. Fundamental Processes

Intercalating agents, such as proflavin, acridine, and ethidium, cause the deletion or addition of a base pair or even a few base pairs.