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TLS Online TPP Program

#Question id: 2858

When lactose enters the cell, it is converted to allolactose. It is allolactose (rather than lactose itself) that controls the Lac repressor. Paradoxically, the conversion of lactose to allolactose is catalyzed by b-galactosidase, itself encoded by one of the lac genes. How is this possible? Which statement is incorrect according lac genes expressions?

#Unit 2. Cellular Organization

  1. The expression of the lac genes is leaky, even when they are repressed, because, allolactose binds to a part of the Lac repressor distinct from its DNA-binding domain.

  2. In the absence of allolactose, the repressor is present in a form that binds its site on DNA (and so keeps the lac genes switched off).

  3. Allolactose has altered the shape of the repressor, the protein can no longer bind DNA, and so the lac genes are no longer repressed.

  4. This leakiness ensures that there is a low level of b-galactosidase in the cell even in the absence of glucose, and so there is enzyme poised to catalyze the conversion of lactose to allolactose.

More Questions
TLS Online TPP Program

#Question id: 31048

#Unit 4. Cell Communication and Cell Signaling

Desensitization response of RTK helps to:
TLS Online TPP Program

#Question id: 3728

#Unit 3. Fundamental Processes

Which is not an activity for DNA polymerase I?
TLS Online TPP Program

#Question id: 21111

#Unit 12. Applied Biology

The ribozymes used to generate virus resistance are which type of molecules
TLS Online TPP Program

#Question id: 8685

#Unit 9. Diversity of Life Forms

Which of the following would be most useful in creating a phylogenetic tree of a taxon?
TLS Online TPP Program

#Question id: 11150

#Unit 7. System Physiology – Animal

Use the information in the table to answer the question.


Calculate the equilibrium potential for potassium. Assume a temperature of 37°C.