Question

1. In your own words, describe the four types of inducible repression. Explain how they cause repression (4 pts each). Identify whether they are cis acting or trans acting (1 pt each).

Answer 1

Answer:

• Inducible repression is common in polycistronic gene expression in prokaryotes.
• The operation of lactose operon can be considered as one example.
• In lac operon absence of lactose leads to the synthesis of repressor from a separate promoter. T
• hese repressor proteins, which are trans acting will binds to specific regions on the DNA called as operator region and induce repression to the operon.
• When lactose is present in the medium, also glucose is absent, the operon gets switched on by removing the repressor.
• The galactose operon in prokaryotes and regulation of galactose metabolism in eukaryotes are inducible. In eukaryotes generally the galactose metabolism is repressed by a trans acting repressor Gal 80.
• The Gal 80 repress the upstream activator protein Gal 4.
• In the presence of lactose this repression is over ruled by another protein which binds to Gal 3. Gal 3 bounded with galactose binds and remove Gal 80 naking Gal 4 free.
• The released Gal 4 activates the galactose metabolism.

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